NEWS

This documents significant changes in the dev branch of ksh 93u+m.
For full details, see the git log at: https://github.com/ksh93/ksh
Uppercase BUG_* IDs are shell bug IDs as used by the Modernish shell library.

2206-10-15:

- Fixed 'printf %#H' URL pecent-encoding to be locale-independent. Bytes
  that are invalid multibyte sequences in the current locale are no longer
  encoded as %3F (the question mark). No change for valid characters. Issue
  introduced on 2020-08-10. ('printf %H', HTML encoding, is not changed.)

2026-10-14:

- Fixed spurious "section not found" error message fon an invalid option
  that starts with ++ (for commands that support these).

2026-10-13:

- Fixed a bug in the 'kill' builtin: the arguments -ERR, -KEYBD, and -DEBUG
  were incorrectly accepted and translated to invalid signal numbers.

- Fixed a bug in shell option handling where an initial ++ produced incorrect
  and inconsistent behaviour. The ++ prefix now correctly turns off a shell
  option by its long-form name like + does for single-letter options. This
  applies to ksh command line invocation options as well.

- Fixed a crash upon assigning to .sh.command within a DEBUG trap action.

- Fixed a crash upon assigning an array to .sh.edtext within a KEYBD trap.

2026-10-10:

- Fixed a bug that caused the emacs and vi editor modes to treat multibyte
  spaces as non-space characters.

2026-10-08:

- Fixed the calculation of the width of the line editor prompt on the terminal
  when the prompt includes ANSI escape codes with CSI intermediate bytes.

2026-10-06:

- Fixed a potential crash upon failure to write to the shell history file.

- Fixed the shell seemingly freezing (in fact, taking several minutes) while
  processing certain repetition patterns against a long string. Reproducer:
	[[ $(printf 'ab%.0s' {0..99999}) == +(ab)* ]]
  This now uses an optimised algorithm that takes only a fraction of a second.
  (Note: before yesterday's fix below, this reproducer crashed the shell.)

2026-10-04:

- Refactored the regular expression and shell glob pattern engine to fix a
  crash (caused by excessive recursion) if a pattern with a repetition
  operator was matched against a string with a large number of matching
  elements. Example: [[ $(printf 'a%.0s' {0..99999}) == +(a) ]] now
  correctly matches the string of 10,000 'a's against the +(a) pattern.

- Fixed a small memory leak occurring the first time a pattern matching
  operation sets the .sh.match array.

2026-10-01:

- Fixed a bug in the ${parameter/pattern/string}, ${parameter//pattern/string},
  ${parameter/#pattern/string} and ${parameter/#%pattern/string} expansions: in
  the replacement 'string' (which may contain subpattern references like \1,
  \2, etc. and supports backslash escaping), the shell failed to remove an
  escaping backslash preceding the characters '/', '-', '<' and '>'.

- Fixed: if a variable has one or more shell discipline functions
  (.get, .getn, .set, and/or .unset) associated with it in the main shell
  environment, and these are then redefined in a subshell, the main
  environment's discipline functions were lost. They are now preserved and
  restored properly.

- Fixed an excessive recursion problem in the regex engine that caused a
  crash if very long strings were compared using [[ ... == ... ]] (even if
  the right-hand side does not contain any pattern operators).

2026-09-29:

- The hash table entries (a.k.a. tracked aliases) as shown by the 'hash' and
  'alias -t' commands are no longer ignored when running an external command
  and are now used to optimise the $PATH search. If the result of a previous
  $PATH search was stored in the hash table, that path is tried first. If it
  is not found (e.g., because the command was moved), the shell falls back
  to a full $PATH search and updates the hash table entry. There should not
  be any behaviour change in ksh except a slight speed optimisation.

2026-09-27:

- Fixed bugs in -G/--globstar, all concerning symbolic links to directories:
  1. If a ** pattern component is followed by further pattern, then a
     preceding symlink specified by literal name or matched by a regular
     (non-**) pattern component, as in 'symlink/**/file', matched nothing.
  2. A symlink matched by a regular pattern component was not followed
     consistently: '**/symlink/**' worked, but '**/symlink/**/file' didn't.
  3. A ** pattern component did recursive matching through a symlink that it
     had matched, but only if the ** was the last element in the pattern:
     'dir/**' descended into a symlink, but 'dir/**/file' didn't. A ** now
     never recurses through a symlink. The symlink is now resolved as needed
     to match the rest of the pattern, and not at all if there is no rest.

2026-09-26:

- Fixed a regression in nested compound variable assignment, introduced on
  2026-09-21, where a compound variable written as a list of assignments
  without semicolons was misparsed as an array value. For example,
  'typeset -a ecv=(((y=76 x=12))); typeset -p ecv' incorrectly created
  ecv[0] as an indexed array holding the string '(x=12;y=76)'.

2026-09-25:

- Fixed the interactive shell freezing if a pipeline was suspended (^Z)
  whose last element runs in the current shell environment, such as the
  'read' built-in in 'sleep 10 | read'.

- Fixed: in ${var%word} and ${var%%word}, any unescaped '|' in 'word' was
  incorrectly treated as an alternation operator, even without the @(...|...)
  syntax required to enable this; it is now treated as a literal character as
  documented (and as always in ${var#word} and ${var##word}). Scripts that
  rely on this bug should be corrected to use, e.g., ${var%@(word1|word2)}.

- Fixed the syntax of an empty compound variable in 'typeset -p' output.

2026-09-23:

- Fixed failures (assignment data loss) when a nested associative array was
  assigned to a name reference that pointed to a variable in a calling
  function's local scope.

2026-09-21:

- Fixed a bug in nested indexed array assignments where values that happened
  to be the names of declaration commands would be executed as those
  declaration commands. For example, arr=((a b c)(typeset -p PATH)) now
  works correctly by assigning 'typeset', '-p' and 'PATH' as array values to
  arr[1][0], arr[1][1] and arr[1][2] instead of executing 'typeset -p PATH'.

- Fixed a buffer overflow that could occur when creating a type with
  'typeset -T', creating a function, then attempting to use 'typeset -p'.

2026-09-19:

- Fixed a longstanding bug where already-assigned associative array elements
  cannot be used in default assignment values of another element of same
  array -- for example, ${x[1]:=${x[0]}} failed to work correctly.

- Fixed default assignments on unset associative array elements, e.g.
  ${x[sub]=value} or ${x[sub]:=value}, which failed to assign the value to
  the element and instead left it empty or nonexistent.

- Fixed a bug in unsetting an associative array where the values of the array
  would be cleared but the former array variable still had leftover attributes.

2026-09-17:

- Fixed multiple memory leaks occurring upon subshell exit when assigning a
  value to a variable with a shell discipline function within a subshell.

- Fixed a crash occurring when assigning, within a subshell, an invalid
  value to a variable of a type defined by the 'enum' command.

2026-09-16:

- Fixed: when the special IFS (field splitting characters) variable was
  assigned to within a ${ shared-state command substitution }, the state of IFS
  failed to persist beyond it, and a use after free (potential crash) occurred.

- Fixed bounds checking when assigning to fixed-size arrays (declared like,
  e.g., 'typeset -a array[4]'). Assigning to an out-of-range subscript now
  produces the expected error instead of potentially crashing.

2026-09-15:

- Fixed a memory leak when assigning, within a subshell, a value to a
  special variable (one of IFS, FPATH, CDPATH, SHELL, ENV, VISUAL, EDITOR,
  HISTFILE, OPTIND, SECONDS, RANDOM,.sh.match, .sh.version, LINENO, _,
  LC_CTYPE, LC_NUMERIC, LC_COLLATE, LC_MESSAGES, LC_ALL, and LANG).

2026-09-13:

- Fixed a memory leak that occurred when converting an existing scalar
  variable to an associative array using 'typeset -A'.

2026-09-12:

- Implemented advisory locking for $HISTFILE (~/.sh_history by default) so
  that multiple ksh instances can write to the history file without risking
  data loss when one of them decides to trim the file. Note that ksh
  versions before 2026-09-12 will ignore the lock, so the risk continues to
  exist if an older ksh binary shares write access to the file.

- History file trimming no longer requires write access to the directory in
  which the history file resides and will no longer change the directory's
  last-modified timestamp. However, it now requires a usable /tmp or $TMPDIR.

- I/O errors while writing to the history file are no longer silently ignored.

- Fixed a possible crash when attempting to set an integer variable to a
  multibyte character.

2026-09-10:

- Fixed a rare crash that could occur if a signal (such as interrupt, Ctrl+C)
  occurred while cleaning up the state of a virtual subshell upon its exit.

2026-09-08:

- Fixed: PWD and ENV were not properly reinitialised when executing a shell
  script without a #! path.

- Fixed a possible crash after unsetting RANDOM. Bug introduced on 2022-07-21.

2026-09-04:

- Fixed a longstanding bug in which output data loss or corruption could
  intermittently occur if, within a command substitution, standard error is
  redirected to standard output and, within that redirection, standard
  output is then connected to a pipe.

2026-09-02:

- Fixed a bug, introduced on 2025-05-30, that made 'print -s' ineffective
  at writing to the history file. This functionality is now restored.

2026-08-31:

- Fixed a crash in the expr(1) path-bound built-in command that could occur
  when using the non-standard 'match' or 'index' keyword.

2026-08-30:

- Fixed a bug that caused non-importable environment variables (i.e., those
  with names that are not valid shell variable names) to disappear from the
  environment of child processes after invoking more than two external
  commands, potentially crashing the shell. Bug introduced on 2025-05-30.

2026-08-29:

- If an error (such as a syntax error) occurs in a trap action, the error
  message will now have the word "(trap)" in the call stack for clarity.

2026-08-26:

- Following up to 2026-08-16, fixed a remaining problem in the 'read'
  built-in with combined -d and -n options when reading from a pipe; the
  custom delimiter is now correctly used instead of newline.

2026-08-16:

- Fixed a long-standing bug in the 'read' built-in: the -d option was
  ignored when combined with -n. The two options can now be used together.

2026-08-14:

- In the --man/--help output for built-in commands, text marked as italic
  is no longer rendered as bold + underlined, but only as underlined.

2026-08-13:

- Fixed corruption of $_, crashing the shell upon 'typeset -p _', after an
  error occurs trying to redefine a type defined with 'typeset -T'.

2026-08-06:

- Fixed ksh crashing upon parsing a very long list of simple commands
  separated by semicolons or, in 'eval' or dot script contexts, by newlines.

- [v1.1] The -n/--noexec option can now effectively be set in subshells of
  interactive shells, e.g., within a parentheses block.

- [v1.1] The 'eval' command has a new -n/--noexec option that causes it to
  subject the command(s) given to static analysis in the manner of the
  -n/--noexec shell option, emitting warnings for deprecated usages.

2026-08-04:

- Fixed a potential crash when suspending (^Z), on the interactive shell,
  a multi-element pipeline with the last element running in the current
  environment.

- For non-interactive shells, the COLUMNS and LINES variables now initially
  respect their values inherited from the environment, if any. They will
  still be updated upon the next window size change (SIGWINCH) or, on the
  interactive shell, when any external command returns. This change aligns
  ksh with bash in supporting idioms like:
	$ COLUMNS=60 ksh somescript.ksh
	$ COLUMNS=60 print --man

2026-08-03:

- Fixed crashes that could occur when an arithmetic syntax error is thrown
  in an arithmetic expression processed via the print or printf built-ins.

- ksh no longer crashes or misbehaves when an arithmetic expression
  longer than 32767 bytes contains an array subscript.

2026-08-01:

- Fixed bogus expansion values of ${var/#pattern/replacement} or
  ${var/%pattern/replacement} that occurred when var is unset.

- Substring matching operations on .sh.match itself now work correctly,
  e.g.: digits_only=${.sh.match[0]//[^0-9]/}
  Note that such operations do still immediately update .sh.match.

- Fixed a segfault upon, e.g., "${.sh.match[@]} ${.sh.match[@]/a/A}".

2026-07-26:

- Fixed problems in the mv(1) and cp(1) path-bound built-in commands:
  - mv(1) now correctly moves entire directory hierarchies across file systems.
  - Non-recursive cp(1) no longer attempts to copy a directory as a plain file.
  - cp(1) now correctly copies special files such as FIFOs.
  - A nonexistent destination directory now results in a useful error message.

2026-07-25:

- For 'printf %T' and the date(1) builtin, multiple problems have been
  fixed with the conversion of Daylight Savings Time offsets, as well as
  contemporaneous time zones.

- Fixed a bug, introduced on 2024-01-16, where 'typeset -r y=${x[0].a}'
  would cause typeset to throw a spurious "invalid variable name" error
  due to the ]. in the ${x[0].a} expansion.

2026-07-24:

- Fix for 'read -t': the timeout was not deactivated if the read operation
  was interrupted before the timeout occurred. On interactive shells, after
  Ctrl+C, this caused command line entry to be interrupted by that timeout.

2026-07-21:

- Fixed a crash when attempting to access a positional parameter with a
  number exceeding PTRDIFF_MAX (or, until 2026-04-14, INT_MAX).

2026-07-20:

- Fixed a use-after-free in optget(3) long-form option parsing.

- Fixed an invalid free that occurred upon exiting the subshell when
  attempting to assign to an array subscript of .sh in a subshell.

2026-07-19:

- Fixed various potential crashes and misbehaviour due to the use of
  uninitialised memory.

2026-07-18:

- Fixed a crash that occurred when an unterminated command substitution
  follows a here-document redirection. For example, ksh -c $'cat <<EOF $(\n'
  now throws the expected syntax error without crashing.

2026-07-17:

- The 2020-09-05/2021-04-30/2021-05-03 fix for erroneous syntax errors in
  parameter expansions such as ${var:-wor)d} or ${var+w(ord} was ineffective
  for positional parameters (e.g., ${1:-wor)d} or ${2+w(ord}) due to an
  additional problem in the lexer, which has now been found and fixed.

- Fixed a potential crash or freeze in the processing of an unterminated
  here-document combined with a pattern matching redirection.

2026-07-16:

- Fixed: assigning a value to a 'typeset -b' binary data variable that is
  shorter than the previous value caused the shell to crash or output garbage.

- The shell's timer/alarm-related features ($TMOUT, 'read -t', the 'alarm'
  built-in, and various internal timeout handling) now use the POSIX functions
  timer_create(2) and friends with CLOCK_MONOTONIC, where available. This
  guarantees a correct delay even if the system clock is adjusted during it.

2026-07-15:

- Fixed: the value of $? was incorrectly 0 in the EXIT trap when the shell
  aborted due to an error.

- Fixed: $((-2**63/-1)) threw SIGFPE or froze the shell.

2026-07-13:

- Fixed: when the -m option is turned on in a non-interactive shell, and the
  shell controls a terminal, the terminal foreground process group ID was not
  set correctly when running external commands. Bug introduced on 2026-07-01.

2026-07-06:

- Fixed: on the shell's invocation, the -s option (read script from standard
  input) was incorrectly forced on if -c was used to pass a shell script as
  a command line argument without passing any further arguments.

- Fixed a bug where read -nN would fail in a -c script when reading from a
  pipe, e.g., this failed: print xyz | ksh -c 'read -n2 && print "$REPLY"'.
  Bug introduced on 2026-04-17.

2026-07-03:

- Fixed a bug in the printf built-in where the output of %.Ng, where N is
  a number of digits > 18, was truncated for numbers longer than 18 digits.

2026-07-02:

- Process substitution now no longer depends on compile-time detection of
  /dev/fd/N, but detects this at runtime instead and transparently falls
  back to the legacy method with FIFOs whenever /dev/fd is unavailable. This
  fixes process substitution on FreeBSD, where /dev/fd is an optional file
  system that may be mounted and unmounted at any time.

- Fixed input buffer memory corruption occurring for inpnut from the terminal
  and other non-seekable input on FreeBSD. Bug introduced on 2026-04-17.

2026-07-01:

- Fixed two longstanding bugs in job control: if the -m (--monitor) option was
  on in a script, then:
  - subshells invoked by the main shell environment did not become the
    leader of their own process group;
  - if the shell was built with the SHOPT_SPAWN compile-time option active
    (default on most systems), then external non-background commands invoked
    from the script didn't become the leader of their own process group.

- Fixed a race condition in job control where all processes belonging
  to a pipeline would not always be assigned the same process group.
  Bug introduced on 2021-02-11.

2026-06-28:

- Fixed a bug in job control that broke job search by command line; instead
  of searching the whole jobs list, a command like 'fg %?STRING' only matched
  STRING for the first job in the list. Bug introduced on 2022-01-02.

2026-06-19:

- Fixed a memory leak that occurred when using printf date/time formatting
  (i.e., %(...)T) with a user-supplied date/time.

2026-06-14:

- Fixed a potential crash (use after free) that could occur if a multi-line
  alias redefines itself while its value is being parsed and executed.

2026-05-08:

- Fixed a bug in the POSIX mode 'getopts', introduced 2026-05-02, where OPTIND
  was increased by one too many at the end of options, causing the idiomatic
  'shift $((OPTIND-1))' command to shift out one non-option argument too many.

2026-05-02:

- When a function that uses the 'getopts' built-in command is invoked from
  the interactive command line with one of the AST self-documentation options
  such as --help or --man, 'getopts' will no longer stop the execution of any
  commands that follow the function call on the same command line.

- The shell's POSIX mode has been amended to disable long options (including
  --help, etc., which would abort the script), which are incompatible with
  the POSIX spec and may prevent POSIX scripts from printing their own usage
  message. This is only disabled if the --posix option is on *and* getopts is
  given an options string that does not use ksh's extended getopts interface.

2026-04-22:

- Fixed a bug that causes the loss of the contents of all here-documents
  in already-loaded functions if a command on the interactive shell is
  interrupted, such as with Ctrl+C. Bug introduced on 2024-02-22.

2026-04-20:

- [v1.1] Removed an undocumented and inconsistent hack that made
	ksh somecommand arg1 arg2 arg3
  equivalent to
	ksh -c 'somecommand "$@"' dummy arg1 arg2 arg3
  if, and only if, the command "somecommand" was not found on $PATH. For
  instance, the command
	ksh print hello there
  would output "hello there" if the command 'print' didn't exist as an
  external command, whereas
	ksh echo hello there
  would usually fail as ksh tried to execute /bin/echo as a shell script,
  because 'echo' usually exists on PATH as an external command. This
  inconsistency, among others, is the reason why the correct documented -c
  usage is now required. One other important effect of this fix is that
	ksh --noexec nonexistent_script
  i.e., running the ksh linter a script with a typo in the file name, will
  now produce the expected error message and no longer quietly "succeed".

2026-04-17:

- Fixed a severe problem with invalid buffer handling in the shell's lexical
  analysis and parsing of scripts that could cause spurious syntax errors or
  crash the shell if the size of a script exceeded the buffer size of 64 KiB
  and certain grammatical constructs happened to cross buffer boundaries. To
  prevent this, the entire script is now buffered in memory before parsing
  commences. If the script file size cannot be determined (when loading from
  a pipe), the shell now allocates a fixed-size 2 MiB buffer and scripts are
  buffered one line at a time with a maximum length of 2 MiB per script line.
  The problem now fixed has been present since the early days of AT&T ksh93.

2026-04-16:

- Fixed breakage in autoload loop detection when first invoking an
  autoloadable function on FPATH from within a subshell.

2026-04-14:

- Ksh is now capable of allocating memory within a 64-bit address space. This
  means variables can now contain multi-gigabyte values without ksh crashing.

2026-04-13:

- Fixed a potential crash that could occur if a shell discipline function
  throws an error (such as 'parameter not set' if the -u option is on).

2026-04-12:

- The 2023-02-22 fix for detecting errors while reading a script has been
  fixed to also detect errors while reading a compound command from a script.

- Fixed a corner case bug where backslash line continuation inserted within a
  variable name passed to a declaration command produdced incorrect results.
  This bug was introduced on 2024-01-16 and exacerbated on 2025-05-29.

2026-04-01:

- Fixed a bug where a DEBUG trap containing a function definition would fail
  with a spurious error message when invoked by running a compound assignment.

2026-03-28:

- Fixed a potential crash (buffer read overflow) in the .sh.match code
  that was backported on 2022-02-08.

- Fixed a crash in option parsing that could happen if a multibyte character
  was passed as an option to a command.

2026-03-23:

- Fixed a bug in command substitutions, where a command substitution would
  fail to catch standard output after a nested function redirects standard
  output to /dev/null. Bug introduced on 2022-01-11.

2026-03-22:

- Fixed a bug where the interactive shell would sometimes suspend itself
  after suspending a child process with SIGTSTP (Ctrl+Z).

2026-03-20:

- Fixed a memory leak that occurred when any subshell or ksh function with
  'function name' syntax is invoked while at least one signal or EXIT trap
  is set in the invoking environment.

- Fixed an issue, introduced on 2022-06-13, causing a subshell to fork
  unnecessarily if an EXIT pseudosignal trap is set within it.

2026-03-16:

- Fixed a bug in the join(1) built-in command (bound to /opt/ast/bin) that
  caused it to fail if one of the file arguments is a process substitution or
  other unseekable file stream. Unseekable files were only handled correctly
  when passing "-" for standard input; now all unseekable files work.

2026-03-09:

- Fixed a bug in the sleep built-in command that could cause an excessive
  sleep duration if a signal was received during the sleep.

2026-03-07:

- Fixed an invalid free crash that could occur when using the libcmd
  builtins with /opt/ast/bin prefixed in the PATH and the POSIXLY_CORRECT
  environment variable set to 1.

2026-03-01:

- Fixed a use-after-free crash that could occur when variables of custom
  types defined with 'typeset -T' were used as members of other custom types
  defined with 'typeset -T'.

2026-02-24:

- The routine that prints the menu for the 'select' loop has been made aware
  of multibyte character locales, so that using UTF-8 characters will no
  longer result in menu columns that are not properly lined up.

2026-02-17:

- Fixed a regression introduced on 02-02-2022 occurring on systems with
  glibc 2.35+ that could cause the pty regression tests to crash or lockup.

- Fixed a regression introduced on 02-02-2022 that could cause ksh to crash
  after a command fails with E2BIG.

- Fixed a bug that caused a file descriptor leak when a command run
  with the 'command' builtin couldn't be executed due to an error
  (e.g. ENOENT or E2BIG).

2026-02-15:

- Fixed a bug in 'ksh -n' that caused the shell to overlook many
  obsolete options passed to set(1) and alias(1) and incorrectly
  flag non-obsolete options as obsolete.

2026-02-06:

- Fixed a file descriptor leak introduced in 93u+ 2012-07-27 that occurred
  when forking nested subshells.

- Fixed a bug that could cause cd(1) to fail with the wrong error message
  if the underlying close(2) calls failed after cd failed to change the
  directory with fchdir(2).

- [v1.1] Fixed a file descriptor leak that could occur on systems lacking a
  usable implementation of arc4random(3).

2026-02-04:

- Fixed a severe arithmetic bug (which thankfully never made it into a release
  version) introduced on 2024-11-30, in which 'typeset -i' variables were
  incorrectly treated as unsigned int when rendering their values as strings
  (e.g. 'typeset -i foo=-1; echo $foo' output 4294967295 instead of -1).

2026-02-01:

- Replaced the 2021-03-09 fix for ${!foo@} and ${!foo*}, which was not quite
  correct, with a new fix that also corrects ${#foo@} and ${#foo*}; these now
  also count 'foo' itself as a variable whose name begins with 'foo'.

- Fixed a possible out of bounds crash that could occur when running
  a POSIX function (aka a function of the form 'name() {').

2026-01-28:

- [v1.1] Backported 'builtin -p' and 'umask -p' from ksh93v-, which
  can be used to print reinputtable commands for recreating the builtin
  table state and umask.

- [v1.1] Backported 'trap -l' from ksh93v- for listing signals.

- Fixed a regression, introduced with the printf fixes on 2023-05-18, that
  broke date specs relative to now, such as: printf '%T\n' 'in 10 weeks'

- Fixed incorrect behaviour that occurred when IFS, PATH, SHELL,
  FPATH, CDPATH, SECONDS, ENV, LANG, LC_ALL, LC_CTYPE, LC_MESSAGES,
  LC_COLLATE, LC_NUMERIC, or LC_TIME were declared as a local
  variable within a function using 'typeset' while a custom shell
  discipline function was defined for them in the global scope.

- Fixed memory fault when attempting to run /dev/fd/1 as a script.

- Fixed the value of $0 when running a /dev/fd file descriptor as a script.

2026-01-21:

- Fixed several IFS field splitting bugs in read(1) that occurred
  when it is given a null delimiter (read -d '').

2025-09-30:

- The rm path-bound built-in command from libcmd no longer suppresses error
  messages when the -f/--force option is used.

2025-06-14:

- Fixed a bug occurring on systems with posix_spawn(3), spawnve(2), and
  spawn(2), which when exploited could cause ksh93 to execute scripts
  without a shebang with a shell other than itself, provided /bin/ksh
  was hijacked, or in the case of ksh being unable to obtain it's own
  executable path, whatever the SHELL variable was set to.

- Fixed a bug that could cause scripts without a shebang to run
  without POSIX mode enabled when executed in a virtual subshell.

- Fixed a bug that could allow an attacker to hijack ksh93 during
  shell initialization to execv a shell other than ksh itself, leading to
  the ksh process being surreptitiously replaced with bash, zsh, or
  really anything, provided the binary name ends with the letters
  'sh'.

2025-05-31:

- Fixed a bug that caused the multiline option to break when PS*
  prompts use the kitty terminal's escape sequence (e.g. $'\E[4:4m'
  in the PS1 prompt for formatting spaced dots).

2025-05-29:

- Fixed a serious but rarely occurring regression that corrupts variable
  names in assignments. It could be triggered in large scripts and cause a
  spurious "invalid variable name" error. Bug introduced on 2024-01-16.

- Restored the ability to import environment variables with multibyte UTF-8
  names while in a UTF-8 locale. This broke on 2020-09-26.

2025-05-27:

- Fixed a crash that could occur in some scenarios when /opt/ast/bin
  builtins handled invalid options in virtual subshells.

- Fixed a bug in printf where \u0025 was taken as a % operator in a
  formatter argument. For example, printf '\u0025\n' now correctly prints a
  % followed by a newline instead of producing an error.

- [v1.1] Fixed another bug with superfluous operands in test/[ that slipped
  through the cracks on 2024-12-08: test -n -a "" incorrectly returned 0. In
  native mode, this is now an error (superfluous operand to the unary -n
  operator) and in POSIX mode, it returns 1/false, as POSIX-1.2017 rules
  require this to be a test for the non-emptiness of both strings -n and "".

2025-05-26:

- Fixed a POSIX mode bug in test/[ (with 'posix' shell option on):
  * test ! foo -o bar	wrongly returned 0/true, now returns 1/false.
  * test ! foo -a ''	wrongly returned 1/false, now returns 0/true.
  This regression was introduced on 2021-11-13.

- Made the handling of deprecated parenthesis operators in test/[ slightly
  more permissive for increased compatibility with other shells and external
  test/[ commands.

2025-05-15:

- Fixed an issue that prevented Unicode code points in $'...' strings and
  printf(1) formatters from being converted to the current locale. For
  example, if the locale on Linux/BSD/macOS is el_GR.ISO8859-7, echo $'\u03B1'
  now outputs a Greek lower-case alpha encoded in ISO8859-7 ($'\xE1').

2025-05-10:

- Fixed a memory leak in history expansion.

- Fixed a crash in 'fc -p'/'hist -p' that occurred when an incorrect history
  expansion followed a correct one in the command operands.

2025-05-08:

- [v1.1] Fixed: case modification expansions (added on 2025-04-23) were not
  properly subject to field splitting and pathname expansion if unquoted.

2025-05-05:

- [v1.1] grep(1) has been added as a path-bound built-in command. It is now
  available by default on ksh linked against dynamic libcmd, and may
  optionally be included in ksh linked against static libcmd. This grep
  supports eight kinds of regex, including sh and ksh glob patterns.

2025-05-02:

- [v1.1] Self-documentation output from any command's --man, --help, and
  other options is no longer written to standard error with exit status 2,
  but now goes to standard output and sets exit status 0. For an overview
  of self-documentation features, type: 'print "--???"'.

- When ksh is linked against the dynamic libshell/cmd/ast libraries (when
  building ksh on supported systems), all of the built-in commands from libcmd
  are now made available by default, bound to the virtual path /opt/ast/bin.

2025-04-29:

- [v1.1] The 'case' compound command now supports the ;;& control operator
  as on bash 4.0+. The ;;& operator falls through like ;& but executes the
  next matching list instead of simply executing the next list.

2025-04-27:

- [v1.1] The emacs mode now accepts a numeric repeat parameter for ordinary
  character insertion. For example, ESC 10 x will insert 'x' 10 times.

2025-04-24:

- Fixed a bug in the expansion of $* within a here-document: the positional
  parameters were separated by a hardcoded space instead of the first
  character of $IFS (which defaults to a space but can be changed).

2025-04-23:

- [v1.1] Ksh now supports the bash-like case modification expansions
  ${var^pattern}, ${var^^pattern}, ${var,pattern} and ${var,,pattern}.
  These change alphabetic characters in the variable to upper or lower case.
  Unlike in bash, the pattern may match any number of characters.

- The SHOPT_DYNAMIC compile-time option (the ability to load builtins from
  dynamically linked libraries such as libcmd) is now automatically disabled
  for the version of ksh that is linked against the static libast/libcmd/
  libshell libraries, as it cannot work correctly on those. On the version of
  ksh linked against the dynamic version of these libraries (on supported
  systems) it is automatically enabled. Since it is now handled automatically,
  SHOPT_DYNAMIC has been removed from SHOPT.sh as a configurable option.

2025-04-10:

- Fixed a bug (present in all AT&T and 93u+m releases) affecting parsing of
  glob patterns and regular expressions, which caused the following to fail:
    str=aaaa && echo "${str%%aaa}"  # now correctly outputs 'a'
    [[ aaaa =~ aaa$ ]]; echo $?	    # now correctly outputs 0 (true/success)
  and similar, more complicated corner cases involving strings of identical
  characters with a length difference of one.

2025-04-07:

- Fixed a bug where pasting over 80 bytes of multibyte characters into the
  command line over ssh resulted in corrupted input. This problem was caused
  by multibyte characters being split when the typeahead buffer is full.

2025-03-30:

- Fixed: 'stty -echo' failed to turn off echoing of terminal input in
  scripts for subsequent 'read' commands. Bug introduced on 2021-02-11.

- Fixed an issue where any DEBUG trap defined in .kshrc (or other $ENV script)
  was unexpectedly executed for internal 'tput' commands that ksh invokes at
  init (to obtain terminal escape sequences for multiline editing).

2025-03-28:

- Fixed crash upon resizing the terminal window after 'stty -echo', including
  when invoking ksh as a child shell in an editor such as emacs (M-x shell).

- The ESC . and ESC _ commands in emacs/gmacs and the _ command in vi, which
  insert the last word of the last command, now:
  - recognise not only spaces but also the following shell grammar
    characters as word boundaries: |&;()`<>
  - correctly recognise a word that is quoted with the $'...' syntax,
    even when it includes a backslash-escaped single quote.

- [v1.1] The 'cd' command no longer adds brackets to system error messages.

2025-03-24:

- Fixed a crash that occurred in specific circumstances when processing a
  here-document within a command substitution within another here-document.

2025-03-21:

- Fixed a corner case bug in the "$*" expansion: spurious backslashes were
  inserted for empty parameters if IFS has the empty value (meaning, no
  output field separator). For example:
	(set -- a '' b '' c; IFS=''; echo "$*")
  wrote a\b\c but now again writes abc. Bug introduced on 2022-07-28.

2025-03-20:

- Fixed a corner case bug in ksh's printf built-in: if there was a gap in
  index conversion specifiers (for example, %5$s, the string with index 5,
  given without %4$s, %3%s or %2%s), then ksh incorrectly executed the
  string arguments corresponding to the gap as arithmetic expressions.

2025-01-15:

- [v1.1] The $RANDOM pseudorandom numbers are now generated by nrand48(3)
  instead of rand_r(3). Since POSIX specifies a particular pseudorandom
  generator for nrand48, this means the same pseudorandom sequence should now
  be generated on all platforms if RANDOM is assigned the same seed value.

2025-01-08:

- Fixed buggy emacs mode behaviour on exceeding the maximum line length.

2025-01-07:

- Fixed the expansion ${variable//""/string}; since the shell pattern is
  empty, this should output the value of the variable unchanged, and now
  once again does. Bug introduced on 2023-03-29.

- Fixed multibyte processing in the expansion ${variable//~(E)/string},
  i.e., the pattern is an empty Extended Regular Expression (ERE). This
  now inserts string between each character instead of each byte.

2025-01-05:

- Fixed a crash that could occur if a discipline function was first assigned
  to a variable in a virtual subshell before the variable was scoped to that
  subshell, then upon subshell completion another discipline function of the
  same type was assigned to that selfsame variable in the parent shell.

2025-01-03:

- The performance of virtual subshells has been significantly improved by
  avoiding unnecessary syscalls to save and restore the working directory.
  Thanks to Johnothan King for backporting and improving the AT&T 93v- code.

2024-12-30:

- The KEYBD trap should now be fully functional for multibyte characters
  (for example, non-Latin characters in UTF-8 locales). This fixes a bug
  inherited from AT&T and worked around on 2022-02-12.

2024-12-29:

- [v1.1] The emacs ^Y command now accepts a numeric parameter. For example,
  ESC 10 ^Y will now "yank" (paste) the latest deleted text 10 times.

2024-12-25:

- The dirname path-bound built-in now accepts multiple operands.

- The basename and dirname path-bound built-ins now have a -z/--zero option
  for compatibility with the GNU versions of these utilities. It causes the
  line terminator to be a zero byte instead of a newline.

- Fixed bugs related to the handling of an initial double slash in the
  basename and dirname path-bound built-ins when used on Windows (Cygwin).

- Fixed a buffer overflow problem in the handling of arithmetic functions.

2024-12-24:

- [v1.1] The fc/hist command has a new -E option. If this option is given,
  the command line that was loaded into the editor will only be executed if
  the temp file is saved before exiting the editor.

- [v1.1] The ^X^E (emacs mode) and v (vi mode) commands will now only
  execute the command line that was loaded into the full-screen editor if
  the temp file is saved before exiting the editor.

2024-12-22:

- In the emacs/gmacs line editor, the ESC [ <letter> macro feature, which is
  documented to input the value of the alias __<letter>, now actually works.
  A decades-old bug in internal variable handling rendered it inoperative.

2024-12-21:

- Fixed a bug in the emacs/gmacs line editor where a command repeat count
  (e.g., ESC 3) sticks and is reused for the next command after an ESC
  command. For example, ESC 3 ESC _ recalls the third word from the last
  command in the history. The bug is that the next command, such as ^B to
  move back, is then repeated three times. Bug introduced on 2020-09-17.

2024-12-18:

- Pursuant to POSIX.1-2024, exec(1) will no longer cause the shell to exit
  when it fails to replace an interactive shell with the given command.

2024-12-08:

- [v1.1] Fixed a bug in the test and [ built-in commands where superfluous
  operands following simple unary or binary expressions were ignored instead
  of throwing an error message.

2024-12-05:

- [v1.1] The appending redirection operator &>>FILE is now available
  (inspired by bash 4.0 and later). It is a shorthand for: >>FILE 2>&1

- Fixed an issue in the vi line editors where lines beginning with whitespace
  could not be recalled from the history (e.g. with arrow up). Bug introduced
  on 2022-10-31.

- Fixed an issue that caused .unset discipline functions (if set) to be
  incorrectly called during cleanup upon terminating a virtual subshell or
  before running a #!-less script.

2024-11-26:

- The -v/--verbose option of the cp, mv and ln built-in commands (which are
  bound to the /opt/ast/bin virtual path by default) was non-functional. The
  option now reports each successful operation in the manner of the *BSD and
  macOS versions of these commands.

2024-11-17:

- Fixed undefined behaviour when passing the floating point values Inf or
  NaN to the 'sleep' built-in command. These now cause 'sleep' to correctly
  sleep forever or print an error message, respectively.

2024-11-15:

- On Android 14 (Termux), the -a option to the 'exec' command is ineffective
  because the OS disallows changing $0 (which is argv[0] in C). ksh now
  detects this condition at compile time and, if detected, makes 'exec' print
  a warning if -a is used, instead of silently failing to set argument zero.

2024-11-14:

- Fixed a crash in option parsing upon encountering an option value to a
  long option that doesn't accept one (e.g., 'set --state=foo' crashed).
  Bug introduced on 2024-08-01.

2024-11-02:

- Fixed: assigning to TMOUT in a virtual subshell was rendering further
  assignments to TMOUT outside of that subshell ineffective.

- Fixed: the 'read' built-in was timing out according to the value of TMOUT
  even when it was not reading from a terminal. The 'read' command will now
  ignore $TMOUT when it is reading from a pipe, as was always documented.
  (Note that read's -t option is not affected by this change.)

2024-10-31:

- Fixed a regression that caused a standard output redirection within a block
  construct to cause inconsistent behaviour or a hang if: (a) standard output
  was also redirected on the block itself, and (b) the entire block was
  executed from within a command substitution. Bug introduced on 2022-01-11.
  Reproducer (should output "OK"): ok=$({ true >&2; } >&2; echo OK); echo $ok

2024-10-27:

- Fixed a bug that crashed the shell upon attempting to replace the shell
  with another command using 'exec' after unsetting the SHLVL variable.
  Bug introduced on 2021-05-18.

2024-10-23:

- Fixed a bug in multidimensional indexed array assignments where unquoted
  values that corresponded to reserved words (such as 'if' or 'select')
  incorrectly caused a syntax error. For example,
    my_array=((somevalue) select) && typeset -p my_array
  now works as expected. This bug was introduced in ksh 93r+ 2006-06-30.

2024-08-28:

- Fixed a crash that occurred for an arithmetic 'for' that has two instead of
  three ';'-separated expressions. The expected syntax error is now given.

2024-08-26:

- Fixed an infinite loop that occurred when a syntax error was thrown
  for an arithmetic 'for' loop on the interactive command line.

- [v1.1] Backported a change to '_' in types from the unreleased ksh 93v-
  beta. If a 'typeset -T' type declaration sets a discipline function for
  one of its subvariables (such as var.get() or var.getn()), then, within
  that discipline function, the automatic '_' nameref now refers to the type
  variable and no longer to the subvariable that the discipline function was
  set for. This means '_' now always refers to the type variable when used
  in a type declaration.

2024-08-22:

- Fixed: command lines containing certain specific kinds of syntax error
  were not entered into the shell's history for retrieval and correction.

2024-08-21:

- Fixed a corner-case crashing bug in shell discipline functions.

2024-08-19:

- Fixed a corner-case bug: for an empty set of positional parameters,
  "$@$@" would generate one empty field instead of zero fields like "$@".

2024-07-31:

- Fixed a bug where printf %T, after having printed the time in UTC once
  with the TZ variable set to "UTC", would always print the time in UTC from
  then on, even if the TZ variable was changed to another time zone.
  Bug introduced in ksh 93t+ 2009-10-21.

2024-07-26:

- Fixed a regression where a broken pipe signal (SIGPIPE), when occurring in
  a pipe construct within a subshell, caused incorrect signal handling in the
  parent/main shell, in some cases causing a script to abort. Bug introduced
  on 2022-07-02.

- Fixed a bug in the pipefail shell option where the status of a signalled
  non-rightmost process in a pipeline was just the signal number, instead of
  that number + 256. Bug introduced in ksh 93u+ 2011-04-15.

2024-07-24:

- Fixed a serious bug in the arithmetic subsystem that was triggered on
  non-Intel processors (such as ARM): any division of an integer by a
  negative integer threw a spurious "divide by zero" error. Bug introduced
  in ksh 93q 2005-01-31.

- Similarly fixed: the return value of the assignment of a negative value to
  an unsigned integer in an arithmetic expression was always 0 on ARM
  processors (instead of being equal to the assigned wrapped-around value).
  Bug introduced by the discipline fix on 2024-01-21.

- [v1.1] In printf formatters and C-style $'quoted' strings, \xNN is now
  limited to two hexadecimal digits (yielding one byte). For multi-byte
  characters, \u and \U should be used instead.

2024-07-21:

- Fixed a long-standing parsing bug: a '((' that was unmatched by
  corresponding closing parentheses and enclosed within a compound command
  failed to throw a syntax error and could cause the shell to crash.

- [v1.1] In emacs mode, pressing ^U (kill) twice no longer causes further
  ^U presses to start a new line (this was a feature for paper terminals).

2024-07-18:

- Fixed a regression where 'read' cannot create a previously nonexistent
  variable when used within a namespace block. Bug introduced on 2023-06-02.

2024-07-17:

- Fixed: if the --posix or --letoctal option was turned on, octal numbers
  designated by the leading-zero octal prefix enabled by these options but
  containing the invalid digits 8 or 9 (e.g., $((09)) or let "09") failed
  to throw an error and were instead incorrectly reinterpreted as decimal.

- Fixed: invalid leading zeros in the '0x' hexadecimal prefix or in ksh
  arithmetic base specifiers, e.g., 00x2F or 016#2F (instead of 0x2F or 16#2F),
  failed to throw an arithmetic syntax error.

2024-07-16:

- The history expansion character ('!' by default) is now not processed when
  immediately following '${'. This makes it possible to use expansion syntax
  like ${!varname} and ${!prefix@} on the interactive command line with the
  histexpand option on; these no longer trigger an "event not found" error.

2024-07-13:

- The shell is now capable of handling more than 32767 simultaneous
  background jobs, subject to system limitations.

2024-07-02:

- Support for UNC paths (//server/dir) is now enabled by default on Cygwin.

2024-06-30:

- Fixed: the 'hash' and 'alias -t' commands no longer autoload functions
  from executable files on FPATH as an unintended side effect.

- [v1.1] The 'hash' and 'alias -t' commands now issue an error message for
  each command given that was not found on PATH, and return a non-zero exit
  status if any of the commands given were not found.

2024-06-27:

- Fixed: a builtin activated with the 'builtin' command was not found if
  invoked within a namespace block on the same line as the 'builtin' command.

2024-06-26:

- Fixed: when the --showme option was used with a command containing multiple
  redirections, only the first redirection was shown, without a newline. This
  bug was introduced along with --showme in ksh 93s- 2006-09-12.

2024-03-05:

- Fixed a corner case bug causing incorrect field splitting behaviour of a
  repeated whitespace character in the IFS variable. The behaviour was
  incorrect when the posix option was changed while xtrace was on, or when a
  shell discipline function was defined for IFS. Bug introduced on 2022-03-05.

2024-03-03:

- Fixed incorrect behaviour of {n1..n2..incr} range brace expansions, which
  sometimes occurred if the value of n1 multiplied by incr falls outside of
  the INT_MIN..INT_MAX range. For instance, {1696512000..1696512000..300}
  now correctly outputs only 1696512000.

2024-03-30:

- A regression was fixed in ordinal specifiers in 'printf %T' date
  specifications. For example,
	printf '%(%F)T\n' '4th tuesday in march 2016'
  wrongly printed '2016-04-09' and now again correctly prints '2016-03-22'.
  This regression was introduced with the printf fixes on 2023-05-18.

2024-03-24:

- We now support building a dynamically linked ksh 93u+m with libast,
  libdll, libcmd, and libshell available as dynamic libraries for other
  applications to use. The dynamically linked version is built in a 'dyn'
  subdirectory; there are no changes to the statically linked version. See
  README.md for more information. Dynamic linking is tested and supported
  on Linux, Android, macOS, FreeBSD, NetBSD, OpenBSD, illumos and Solaris.
  Please test this on other platforms and send us your reports and patches.

2024-03-22:

- Fixed a crash in the getconf built-in that could occur after the 'builtin'
  command was used to bind it to the same path as the external getconf command.

2024-03-20:

- Android with Termux is now a supported environment for ksh 93u+m. Testing
  was done on Android 14.0 with Termux 0.118.0. Please report any breakage.
  Build dependencies (Termux packages): clang, binutils, getconf. Runtime
  dependencies: ncurses-utils (for --multiline), getconf (fallback for the
  /opt/ast/bin/getconf builtin).

2024-03-12:

- Fixed a regression in the 'printf' built-in, introduced on 2023-05-17,
  where each instance of '\0' or '%Z' in the format operand caused a string
  argument to be incorrectly skipped.

2024-03-10:

- Fixed a longstanding bug where the default terminal width for typeset -L, -R,
  or -Z, if not given, was miscalculated for multibyte or control characters.

- Fixed a crash on redefining an array inherited from the parent environment
  in a subshell.

- Fixed corner case breakage of universe handling in the 'echo' command: it
  broke when used in a namespace block before being used anywhere else, and
  only if _AST_FEATURES was not exported first. The bug caused _AST_FEATURES to
  be incorrectly placed in that namespace. Bug introduced on 2023-06-02.

2024-03-07:

- Fixed a bug that caused some systems to corrupt the display of multibyte
  characters in the command prompt.

2024-03-05:

- Fixed a regression, introduced on 2021-02-07, that made the common AST
  options '--???ESC' and '--???noESC' ineffective for enabling/disabling
  ANSI escape codes for emphasis in the output of --man or --help.
  (Type, e.g., print '--???' for more information about common options.)

- Fixed a rare crash in the 'print' built-in due to the use of uninitialised
  memory while parsing options. Bug introduced in ksh 93u+ 2012-05-31.

- Fixed a 2021-04-14 regression: the 'exec' command (which runs a command
  that replaces the shell process and therefore should only run external
  commands) would run a path-bound built-in if /opt/ast/bin is in PATH.

- Fixed a corner case bug: a ${ shared-state command substitution;} failed to
  capture the standard output of a command that replaces the shell via 'exec'.

2024-02-29:

- Improved the robustness of the routines handling the execution by ksh of a
  script without an initial #! path. More memory is freed up after ksh forks.

- Fixed a crash that could occur after 'typeset +x var' when var was imported
  from the environment and then a discipline function was set for it.

2024-02-23:

- [v1.1] The commands ':', 'true', 'false', 'break' and 'continue' have been
  optimised to run faster in loops in certain common cases. For example, the
  'true' in 'while true; do some_stuff || break; done' now runs faster.

2024-02-22:

- Fixed a crash that occurred when starting ksh with no TERM variable in the
  environment (e.g., in single user mode on NetBSD and DragonFlyBSD).

- Fixed a regression of 'return' within traps, reintroduced on 2023-12-25
  after being fixed on 2020-09-09. The regression caused a 'return' or
  'exit' with no arguments to assume the before-trap exit status instead of
  that of the last-run command. This broke the shipped 'autocd' function.

- Fixed some integer overflows that could occur when using TMOUT.

- Fixed a crash on Solaris and illumos when cancelling a here-document
  with ^C or ^D in an interactive shell.

2024-02-17:

- Fixed a crash that could occur when using 'typeset -T' typed variables
  in a virtual subshell.

2024-02-11:

- Added SHOPT_PRINTF_LEGACY compile-time option for compatibility with
  POSIX-ignorant external printf(1) commands that process a format operand
  starting with '-' without the standard preceding '--' options terminator.
  This is for backward compatibility with local system scripts. The
  behaviour of the system's external printf(1) determines whether this is
  compiled in or out by default. Normal ksh printf options keep working.

- Fixed a bug, introduced on 2023-06-02, that made it impossible within a
  namespace to unset a function defined outside the namespace.

- Fixed: ksh didn't pass the exit status of the last command it executed to
  the parent process on entering EOF (Ctrl+D) on a terminal.

2024-02-09:

- Fixed multiple inaccurate or missing values in the /opt/ast/bin/getconf
  path-bound built-in command.

2024-02-08:

- Fixed an init-time crash that may occur if standard error is on a terminal,
  but the path to its tty device can't be found (e.g., in a chroot situation).

- Fixed corrupted output of the 'time' keyword as formatted via TIMEFORMAT on
  systems where sizeof(time_t) != sizeof(int). Bug introduced on 2020-07-13.

2024-02-06:

- Fixed a regression introduced on 2023-03-04 that caused ksh to lock up
  after using the Arch Linux arch-chroot script.

2024-02-03:

- Fixed: the arithmetic representation of negative integers with a base other
  than 10 is no longer incorrectly treated as unsigned long. For example,
	typeset -i16 n=-12; echo $n
  now correctly outputs '-16#c' and no longer outputs '16#fffffffffffffff4'.

2024-01-27:

- Fixed: tilde expansion discipline functions (see 2021-03-16) were not
  reinitialised when executing a ksh script without a #! path line.

2024-01-23:

- Fixed a rare crash or rare incorrect behaviour in .sh.tilde.{get,set}
  discipline functions for ~ expansion (see 2021-03-16 below).

- Fixed a bug that caused listing the .sh.match variable with ${!.sh.match} to
  show spurious elements.

2024-01-22:

- Fixed a bug in the loop invariants optimizer (SHOPT_OPTIMIZE) that caused
  expansions of name references to be incorrectly treated as invariant so they
  yielded the wrong values. Fix backported from from ksh 93v- 2013-02-13.

- Fixed a buffer overflow that could occur when using tab completion
  with multibyte filenames.

2024-01-21:

- [v1.1] New feature added: SRANDOM is a secure random number generator.
  It uses the native OS implementation of arc4random(3) or, absent that, an
  integrated OpenBSD-based version that uses the ChaCha20 cipher. An upper
  bound can be set by assigning its value to SRANDOM; subsequent numbers will
  be uniformly distributed between 0 and the value of the upper bound minus
  one, in a way that avoids "modulo bias". Assigning 0 restores default mode.

- A bug was fixed that caused both the 'set' and 'get'/'getn' discipline
  functions of a variable to be triggered when performing an assignment in
  an arithmetic expression; only the 'set' discipline is now triggered when
  assigning (as was always the documented behaviour). This applies to the
  shell's internal disciplines as well. For example, $RANDOM is no longer
  spuriously read from while seeding it via an arithmetic expression.

- Fixed: assigning to LINENO, RANDOM, or _ via an arithmetic expression gave
  undefined results on systems where sizeof(long double)!=sizeof(double).

2024-01-16:

- Fixed a parsing bug in array subscripts containing '=' in combination with
  a declaration command (such as 'typeset' or 'export'). For instance,
  'typeset -A arr; typeset -i arr[foo=bar]=123' now works correctly.

2024-01-15:

- Fixed a bug, introduced in ksh93q+ 2005-05-22, that stopped an append
  assignment from working together with a declaration command. For example,
  'typeset var+=value' or 'export var+=value' now again work as expected.

2024-01-14:

- Fixed a regression introduced on 2022-11-01 that caused ksh to enter
  an infinite loop after using the up arrow in emacs mode with an empty
  history file.

- Fixed a bug in 'read -s': in a script, the first invocation of that
  command, with the emacs or vi shell option on, did not allow the user to
  navigate through the shell history file.

2024-01-11:

- Fixed ancient incorrect behaviour in the 'kill' built-in: it sent SIGCONT
  to the given process along with every other non-SIGCONT signal issued,
  causing a stopped process to be incorrectly resumed upon sending it any
  signal and causing any SIGCONT trap handler to be incorrectly triggered.

- Fixed: the 'kill' built-in was not able to terminate an interactive shell
  by sending a signal such as SIGHUP to its own shell (e.g. kill -s HUP $$).

2024-01-05:

- Fixed a potential crash on pressing Ctrl+C on the command line while
  history expansion (the -H or histexpand option) is active.

2023-12-28:

- Fixed intermittent incorrect behaviour (a race condition), introduced on
  2023-09-15, that occurred on some systems when running an external command
  with a redirection from a command substitution.

- Fixed an init-time crash on failure to trim the shell command history file
  due to a non-writable parent directory; ksh now prints a warning instead.

2023-12-25:

- Fixed a regression in the behavior of 'exit' in a trap action, introduced
  on 2020-09-09. The default exit status, used when no argument is given to
  'exit', is now once again the exit status of the last command executed
  *before* the trap action, as expected.

2023-09-16:

- The 'kill' built-in command was meant to refuse to issue SIGSTOP to the
  shell's process if the shell is a login shell (because this normally
  causes an unrecoverable freeze of the terminal session). The code
  prohibiting this did not work on modern systems and is now fixed.

2023-09-15:

- Fixed a hang in command substitutions (introduced in 93u+m/1.0.0) that was
  triggered when redirecting standard output within a command substitution,
  in combination with other factors. E.g., the following no longer hangs:
	{ v=$(redirect 2>&1 1>&9); } 9>&1

2023-09-13:

- Fixed a crash on trying to append an indexed array value to an unset name
  reference, e.g.: nameref unsetref; unsetref+=(foo bar). This now produces
  a "removing nameref attribute" warning before performing the assignment.

- Fixed: assignments like name=(...) to arrays did not preserve the array and
  variable types. Fix backported from ksh 93v- beta (2013-07-19, 2013-07-27).

- Fixed: assigning an empty set () to a compound indexed array caused the -C
  attribute to be lost. Fix backported from ksh 93v- beta (2013-09-13).

2023-09-09:

- Fixed incorrect rejection of the tab key while reading input using the `read`
  built-in command. Bugs introduced on 2021-02-26 (emacs) and 2022-08-24 (vi).

- Fixed a minor bug that could cause '/opt/ast/bin/getconf PID_MAX' to
  return the wrong value when ksh is built with strict C99.

- Fixed a bug in printf %T: when using dates and times in the past, time
  zones for the present were incorrectly used, ignoring historical changes.

2023-06-13:

- Fixed a serious regression in pathname expansion where quoted wildcard
  characters were incorrectly expanded if a pattern contains both a brace
  expansion and a variable expansion.

2023-06-12:

- Fixed a bug where ^X^E in emacs or 'v' in vi, which invoke a full-screen
  editor to edit the command line, could cause the wrong command line to be
  edited if two shell sessions share a .sh_history file.

- In the emacs line editor, ^X^E no longer echos the hist command it invokes.

2023-06-10:

- Ksh can now compile on most operating systems when using -std=c99 in CCFLAGS.

2023-06-09:

- Fixed a bug where the 'break' and 'continue' commands stopped working after
  changing scope levels (.sh.level=n) within a loop invoked from a DEBUG trap.

2023-06-05:

- Fixed a bug in command completion: when a shell built-in or defined function
  was preceded in alphabetical order by an undefined function (on FPATH or
  after 'autoload'), the built-in or defined function failed to tab-complete.

2023-06-04:

- Fixed a bug in 'case', introduced in ksh 93t 2008-10-31, where extended
  patterns containing a closing brace ('}') caused a spurious syntax error.

- The POSIX mode was amended to make 'test -e /dev/fd/n' (where n is a file
  descriptor number) actually test for the existence of /dev/fd/n in the
  file system. By default it tests if that file descriptor is open.

2023-06-02:

- Fixed a bug introduced on 2021-04-24 where unsetting a function in a
  subshell hides any built-in command by the same name for the duration
  of that subshell.

2023-05-30:

- Fixed a bug in the 'type -t'/'whence -t' output for an undefined function.

- The autoloadable directory stack and menu-based cd functions in the 'fun'
  directory have been reorganised and fixed to play well together when that
  directory is added to FPATH.

2023-05-29:

- Fixed a bug in bracket expressions in glob patterns where quoting a '!'
  (e.g., to disable its negator function) caused a '\' to be wrongly matched.
  For example,
	case '\' in ['!'X]) echo BAD;; esac
  no longer outputs BAD, and
	touch '\'; ls ['!'X]
  no longer incorrectly lists the file '\'.

2023-05-28:

- Fixed a bug, introduced on 2020-06-08 and exacerbated on 2022-07-02, where
  the exit status of a script did not reflect the signal with the 9th bit
  set if the script exited on receiving a signal and an EXIT trap was set.

2023-05-27:

- Fixed a bug in the handling of backslashes in pathname expansion patterns
  resulting from field splitting. For example, the following:
	$ mkdir testdir; cd testdir; touch b; p='[a\-c]'; echo $p
  now correctly recognises the backslash escape and no longer outputs 'b'.

- The 2023-05-19 fix for brace expansion interfering with extended patterns has
  been improved to also recognise and handle extended patterns that are parts
  of larger patterns, e.g., 'ls file~(E)[[:digit:]]{3,6}\.txt$' now works.

- [v1.1] Added a new 'globex' shell option that causes extended patterns,
  i.e. those with a syntax involving parentheses, to be expanded in fields
  resulting from field splitting. These are normally disabled in that context
  for compatibility with other shells and old ksh versions. For example,
        $ var='~(E)foo'; set --globex; ls $var
  will now list files with names containing 'foo'.

2023-05-19:

- Fixed a bug in the loop invariants optimizer where a variable for which
  a .get or .getn discipline function is set within a loop is incorrectly
  treated as invariant.

- Fixed two bugs in pathname expansion:
  1. Brace expansion interfered with EREs and other extended pattern
     types used with ~(...) pattern option prefixes, e.g. the {3,6} in
     'ls ~(E)^file[[:digit:]]{3,6}\.txt$' was incorrectly parsed as a
     brace expansion instead of an ERE bound matching 3 to 6 digits.
     That command will now list any matching files such as file1234.txt.
  2. With brace expansion disabled (set +B), any '{' character in a file
     name pattern stopped it from being resolved unless a wildcard followed
     it. Now, 'set +B; ls *{' will list files with names ending in '{'.

2023-05-18:

- Fixed multiple bugs causing incorrect output for relative date specifications
  given as arguments to printf %(dateformat)T. For example, something like
	printf '%(%Y-%m-%d %H:%M)T\n' 'exact 9 weeks ago'
  will now produce the correct output, which is the same as GNU date:
	date '+%Y-%m-%d %H:%M' '9 weeks ago'

2023-05-17:

- Fixed buggy behaviour of printf with mix and match of % and %x$.

2023-05-15:

- Fixed a crash on executing a nested compound assignment in a command
  substitution.

2023-05-14:

- If history expansion is active, then command and file name completion now
  quotes the history expansion characters with a backslash as needed to
  avoid triggering history expansion failures if one of those characters
  occurs in a command or file name.

- Fixed completion of file names starting with an escaped literal tilde.

- Undocumented and non-functional goto label functionality has been removed.
  Command names can now end in ':' like on other shells, as POSIX requires.

2023-05-11:

- The ability to use multi-line editing is now detected at runtime instead of
  compile time, making detection more reliable across terminals and platforms.

2023-05-01:

- Fixes for indexed arrays declared to use enum constants for subscripts:
  - Syntax validation: add missing check for ] in 'typeset -a \[type] array'.
  - Fixed error message when type in 'typeset -a \[type] array' is unknown.
  - Fixed 'typeset -p' output of such arrays to quote the square brackets.

2023-04-09:

- Fixed command line redrawing on resizing the window with --multiline off.

- Multiline editing is now automatically disabled if and when the TERM
  environment variable is unset, not exported, or set to a terminal type
  that does not support the necessary operations. It is automatically
  re-enabled when the TERM variable is corrected and --multiline is on.

2023-04-08:

- Fixed a termcap(5) detection bug that broke multiline editing on FreeBSD.

2023-04-05:

- Fixed a spurious syntax error in compound assignments upon encountering a
  pair of repeated opening parentheses '(('. This bug behaved differently
  depending on whether the compound assignment was outside or within a command
  substitution of the form $(...) or ${ ...; }. Both cases are now fixed.

- Fixed a parsing bug in arithmetic functions like
	function .sh.math.add x y { .sh.value=x+y; }
  so that the '.sh.value=x+y' is correctly interpreted as an assignment, not
  as a command name. After this, (( z = add(x,y) )) works correctly.

2023-04-03:

- Fixed multiple crashing bugs in discipline functions invoked from non-forked
  subshells, including corruption of the $_ variable.

2023-04-02:

- Corrected the 2022-07-05 fix for the detection of a syntax error in
  compound assignments to associative arrays.

- Fixed spurious syntax error in ${parameter:offset:length}: the arithmetic
  expressions 'offset' and 'length' may now contain the operators ( ) & |.

2023-03-29:

- Fixed a bug in 'printf -v' (added on 2021-11-18) where using the %B format
  specifier would overwrite any data already written to the variable.

- In the ${parameter/pattern/string} search-and-replace expansion, an
  anchored empty pattern will now match the beginning or the end of the
  string, so that ${parameter/#/string} will prefix the string to the
  parameter value and ${parameter/%/string} will append it. Previously,
  these operations were no-ops (equivalent to ${parameter}). This change
  brings ksh 93u+m into line with mksh, zsh and bash.

2023-03-26:

- Fixed an intermittent crash in 'command -x' experienced on some arm/arm64
  systems running Linux.

- Fixed a bug that caused 'printf "%(%Z)T\n" now' to print nonsense strings
  such as 'ica' on Cygwin.

2023-03-24:

- Fixed a crash in read -d D in multibyte locales that occurred when a byte
  with the 8th bit set was passed as the delimiter character D. For example,
  read -d $'\200' crashed in a UTF-8 locale. (Note that multibyte delimiter
  characters are not supported yet.)

2023-03-23:

- A bug has been fixed in 'printf' and 'print -f' that caused the %a, %A, %e,
  %E, %f, %F, %g, and %G conversion specifiers to evaluate any unexpanded
  arithmetic expression passed to them twice, causing any side effects, such
  as incrementing a variable, to be incorrect. Bug introduced in 93t- (2008).

- The POSIX compatibility mode has been amended to cause 'printf' to parse only
  decimal/hexadecimal/octal constants for its numerical conversion specifiers,
  instead of arithmetic expressions. (POSIX mode does not change 'print -f'.)

2023-03-20:

- Fixed incorrect result of array slicing ${array[@]:offset:length} where
  'length' is a nested expansion involving an array. For example,
  ${array[@]:0:${#array[@]}} is now correctly equivalent to ${array[@]}.

- Fixed bugs in 'command -x' and 'command -v -x' (see 2021-01-30) that caused
  it to fail to disregard built-ins if /opt/ast/bin (the virtual path for
  path-bound built-ins) is in $PATH.

2023-03-19:

- Fixed a crash in 'read' (as well as a spurious error in 'printf -v', added
  on 2021-11-18) when using an indexed array subscript with an arithmetic
  expression that yields 0 while also modifying the variable. For example,
  'i=-1; read a[i+=1]' crashed. Bug introduced in ksh 93s+ 2008-01-31.

- In the 'read' built-in, a '=' in a variable name argument is now once
  again an error and is no longer misparsed as an assignment, which caused
  inconsistent behaviour or (in the case of 'read -C foo=bar') a crash. This
  fixes a bug introduced in ksh 93u+ 2011-04-28.

2023-03-17:

- Fixed nameref self-reference loop detection; as of ksh 93u 2010-11-22, this
  failed for loops of more than two refs. For example, 'nameref a=b b=c c=a'
  now correctly outputs an 'invalid self reference' error message.

2023-03-16:

- Backported a fix from ksh 93v- beta for a bug in the 'for' loop optimizer
  which could falsely treat 'typeset -b' variables as loop invariants.

2023-03-04:

- Fixed a bug introduced on 2022-02-08 that caused string translation using
  $"..." to either crash or fail silently.

2023-03-03:

- A new SHOPT_SCRIPTONLY compile-time option was added that, if enabled,
  compiles out the interactive shell, resulting in a ksh binary that can
  only run scripts. See src/cmd/ksh93/README for more information.

2023-02-23:

- Fixed a crash or corrupted output that occurred on some systems if the vi
  '.' repeater command was used immediately after starting ksh in vi mode.

- In vi mode, when navigating back in the command history and then editing a
  line from the history, the U command now correctly undoes the latest edit
  to the history line instead of jumping back to the current command line.

2023-02-22:

- ksh now throws a panic and exits if a read error (such as an I/O error)
  occurs while trying to read the next command(s) from a running script.
  Previously, ksh acted as if EOF was reached, and the script ended normally.

- The '.' and 'source' commands now throw an error if a dot script can be only
  partially read, instead of ignoring the error. As ksh reads the entire dot
  script before running it, no part of the script is executed in that case.

2023-02-20:

- The SHOPT_RAWONLY compile-time option and the --viraw shell option have been
  removed. Ksh's vi editor now always operates in raw mode (but note that "raw
  only" was already the default compiled-in behaviour as of 93m+ 2002-03-17).

2023-02-16:

- Fixed a bug in 'cd' with no arguments. When changing the working directory
  to the default value ($HOME), it incorrectly used the global scope of the
  HOME variable even if a local scope was active.

2023-01-09:

- Fixed a bug causing incorrect greedy ${.sh.match} results when matching
  the pattern [^]] in a non-ASCII locale.

- Fixed a crash on initialisation that occurred if ksh was launched from a
  parent process with a very high or very low open files limit (ulimit -n).

2023-01-08:

- Fixed a completion bug in vi mode in multibyte character locales, in which
  one or more invalid characters were output at the end of the completion if
  the cursor was on a "wide" character (or if the last character of the word
  is wide and the cursor is in the immediately-following position).

- Fixed a bug in vi and emacs in which using = or * completion from within
  a word failed to replace the word; any trailing characters were printed
  at the end of the completion. (Bolsky and Korn, pp. 105-106 and 114-115)

2022-10-31:

- In vi mode, issuing the v command from a completely empty line now invokes
  the full editor with an empty file instead of beeping.

- Fixed a bug in vi mode where the v command from a line with only whitespace
  resulted in an "invalid range" hist error and the editor failed to open.

- Fixed a bug in emacs mode where calling the full editor saved the current
  command line to the history file without a terminating newline.

- Fixed a bug in emacs and vi modes where navigating to a null or empty
  history line displays an empty line onscreen.

- Fixed a bug in emacs and vi modes where attempting to tab-complete an
  alias or $PATH item containing wide characters failed before the first
  normal-width character had been entered.

2022-10-28:

- [1.1 change] For security reasons, type attributes of variables are no longer
  exported to or imported from the environment. Any script that depends on this
  will need to be changed to typeset the expected attributes itself.

2022-10-18:

- Fixed the expansion of out-of-range \n back references in the string part of
  ${parameter//pattern/string}. For example:  v=AB; echo "${v/@(A)B/\0:\1:\2}"
  now yields 'AB:A:' instead of 'AB:A:\2'.

- Fixed a corner case regression in the BUG_IFSGLOBS fix applied on 2022-07-28:
  unquoted $* was affected. The fix now properly applies only to quoted "$*".

2022-10-14:

- Fixed: the generic --version option was not recognised for the built-in
  commands ., bg, disown, fc, fg, hist, jobs, let, source, times, and ulimit.

- Fixed a bug introduced by the 2022-10-07 BUG_BRACQUOT fix, which caused the
  fallback string in an expansion like ${emptyvar:-fallback string} to fail to
  split into fields correctly if the fallback string contained a !, ^ or -.

- Fixed a few different build errors on Haiku that prevented ksh from compiling
  with the mkservice and eloop builtins enabled, caused compiling with -lnetwork
  to fail, and could interrupt the build with crash report popups.

2022-10-13:

- Added a -V/--novmon option to ulimit that supports setting the number of open
  vnodes (only applies to Haiku).

- Fixed a bug on Haiku that caused the ulimit command to print '(null)' in the
  error string when 'ulimit -t' fails.

- 'ulimit -a' no longer exits immediately after an error occurs when failing
  to get the current limits for cpu time and file size on Haiku.

2022-10-11:

- Fixed a bug that caused inconsistent behavior when handling a dangling
  backslash in a case statement.

2022-10-07:

- Fixed BUG_BRACQUOT: single and double shell quotes did not work to escape
  the !, ^ or - operators in a bracket expression within a glob pattern.

- The -e option of test/[/[[ no longer returns true for pseudodevices that are
  only supported by the shell and do not in fact exist in the file system, such
  as /dev/tcp/*. This reverts a change made in ksh 93u- on 2010-08-24.

2022-09-28:

- Fixed a bug where LINENO was reset to 1 after being temporarily changed in
  an assignment preceding a regular command (e.g. LINENO=5 true).

2022-09-27:

- Fixed a parsing bug in (uncommonly used) function definitions of the
  form 'functname() simple_command' that could cause the first word of
  simple_command to be corrupted with trailing garbage.

2022-09-25:

- Backported support for 'print -u p' from ksh93v- 2014-06-06 (this is
  equivalent to using 'print -p').

- Fixed a bug introduced on 2021-04-04 that incorrectly allowed 'typeset' to
  turn off the readonly and export attributes on a readonly variable.

- Fixed multiple scoping-related bugs in the += additive assignment operator,
  including a bug introduced on 2021-04-11 that caused it to append to the
  value of a global variable when used on a local variable with the same name.

2022-09-24:

- The down arrow key can now be used to perform a backwards reverse search,
  similar to how the up arrow key functions.

- The Page Up and Page Down keys can now also be used to perform reverse
  searches forwards and backwards.

- A new arrowkeysearch shell option can be used to disable backwards reverse
  search using the arrow keys. (Page Up and Page Down will still search).

- In the emacs line editor, the Ctrl+R reverse-search prompt is now visually
  distinct from a literal control character ("^R: " instead of "^R").

- Fixed a crashing bug involving incorrect data alignment in variables of
  types defined by 'typeset -T'.

2022-09-11:

- Fixed a bug introduced in ksh93u+ 2012-04-23 that caused LINENO to have the
  wrong value after parsing a multi-line compound assignment.

- Fixed a bug in vi mode that caused reverse search to remain active after
  receiving an interrupt.

2022-09-01:

- Fixed a bug where 'command -x' would create a tracked alias for a command,
  causing 'whence' not to find an /opt/ast/bin built-in command correctly.

- Fixed a bug in the 'time' keyword where the default precision of a format
  specifier (e.g. %lU) was six instead of three, as documented.

2022-08-30:

- When printing a function definition, 'typeset -f function_name' now
  regenerates the code from the parse tree instead of dumping the literal
  code from the source file. This avoids corrupted or missing output if the
  source file is edited or (re)moved after loading the function. It also
  makes 'typeset -f' function as a code reformatter (AT&T indentation style).

- In the vi line editor, 'C' and 'c$' at the start of a line now enter insert
  mode instead of beeping, and 'I' jumps to the first non-blank character on
  the line instead of the start of the line. These changes are consistent
  with standard vi(1) behavior and with Bolsky & Korn (1995, p. 121).

- Aliases for many GNU long options have been added to the /opt/ast/bin
  built-in commands. Additionally, 'kill -s' now has a --signal long option
  alias compatible with the util-linux option.

- All of the /opt/ast/bin built-ins available in src/lib/libcmd (excluding
  vmstate if vmalloc isn't enabled) can now be enabled with the new
  SHOPT_ALL_LIBCMD setting in src/cmd/ksh93/SHOPT.sh.

2022-08-25:

- In the vi line editor, a bug was fixed that caused erratic behaviour after
  using the 0 or ^ commands when already at the beginning of the command line.

2022-08-24:

- Fixed a bug that caused ksh in the vi editor mode to crash or produce
  invalid completions if ESC = was used at the beginning of a line. Both
  tab and = completions are now disabled at the start of the command line.

- Fixed ksh freezing or using excessive memory if HISTSIZE is assigned a
  pathologically large value. A new bounds check makes the theoretical
  maximum number of history lines equal to the number of bytes kept in the
  history file at cleanup time. On 64-bit systems, that maximum is 16384.

2022-08-20:

- Fixed a bug in command line options processing that caused short-form
  option equivalents on some built-in commands to be ignored after one use,
  e.g., the new read -a equivalent of read -A (introduced on 2022-02-16).

- Fixed a bug in the /opt/ast/bin/cp built-in command that caused the -r and
  -R options to sometimes ignore -P, -L and -H. Additionally, the -r and -R
  options no longer follow symlinks by default.

2022-08-16:

- Fixed an old bug in history expansion (set -H) where any use of the history
  comment character caused processing to be aborted as if it were an invalid
  history expansion. (On 2022-01-24 the history comment character was set to
  '#' instead of being disabled by default, which exposed this bug.)

- Fixed a bug introduced on 2022-02-12 that would cause the optional head
  builtin's -s option to fail.

2022-08-06:

- Fixed an interactive shell crashing on redefining, then unsetting one of
  the predefined aliases.

- Fixed an interactive shell crashing on redefining one of the predefined
  aliases, then executing a shell script that does not start with a #! path.

2022-08-05:

- Reverted a buggy exec optimisation introduced on 2022-06-18. It is known
  to make the build scripts of GNU binutils produce corrupted results.

2022-08-01:
   _        _        ___ _____                          ___   ___   ___
  | | _____| |__    / _ \___ / _   _   _   _ __ ___    / / | / _ \ / _ \
  | |/ / __| '_ \  | (_) ||_ \| | | |_| |_| '_ ` _ \  / /| || | | | | | |
  |   <\__ \ | | |  \__, |__) | |_| |_   _| | | | | |/ / | || |_| | |_| |
  |_|\_\___/_| |_|    /_/____/ \__,_| |_| |_| |_| |_/_/  |_(_)___(_)___/

- Exactly ten years after ksh 93u+ 2012-08-01, we now have a new ksh release.
  Many thanks to all the direct and indirect contributors for their hard work!
  (Note: this applies to the 1.0 branch, but seemed worth mentioning here)

2022-07-28:

- Fixed BUG_IFSGLOBS ("$*" does pattern matching if the first character of
  $IFS is a wildcard).

2022-07-27:

- Fixed a bug introduced on 2022-02-08 where $PPID was incorrect when a script
  without a #! path was executed.

- Fixed a completion bug in the vi line editor. It now correctly completes
  the sole member of a directory when tab is pressed immediately after /.
  Thanks to K. Eugene Carlson for the report and the fix.

2022-07-26:

- Fixed incorrect handling of initial zeros in test/[ and [[ arithmetic
  comparison operators. For example, [[ 0x0A -eq 10 ]] yielded false but
  [[ 1+0x0A -eq 11 ]] yielded true.

- Fixed comparing long floating point (typeset -lF) values in test/[ and [[;
  the values were reduced to standard floating point before comparing.

2022-07-24:

- Add new 'man' function in src/cmd/ksh93/fun/man. This integrates the --man
  self-documentation of ksh built-in and external AST commands with your
  system's 'man' command so you can conveniently use 'man' for all commands,
  whether built-in or external. To use this, put the file in a directory in
  your $FPATH and then issue 'autoload man' in your .kshrc to override the
  system's man(1) command. See the file for details.

- Add new 'autocd' function in src/cmd/ksh93/fun/autocd. This activates a
  feature like 'shopt -s autocd' in bash: type only a directory name to change.
  See the file for details. Add this file to a directory in your $FPATH to use.

- New feature to make 'set -b'/'set -o notify' more usable. When that option
  is on (and either the vi or emacs/gmacs line editor is in use), 'Done' and
  similar notifications from completed background jobs no longer mess up the
  command line you're typing. Instead, the notification is inserted directly
  above the line you're typing, without affecting your command line display.

- Fixed a bug that caused the -b/--notify option to only notify on one job if
  more than one background job completed at the same time.

- Fixed a bug in the 'command -x' feature introduced on 2021-01-30; it is meant
  to always run an external command, but failed to bypass path-bound builtins.

2022-07-21:

- Fixed a bug where a reproducible $RANDOM sequence (after assigning a
  specific value to $RANDOM) was influenced by running any external command.

- When an error occurs in a POSIX name() function or a dot script, the
  function or script name is now reported in the error message.

2022-07-14:

- Fixed a bug that caused a spurious "Done" message on the interactive shell
  when an external command was run as a foreground job from a SIGINT trap.

2022-07-12:

- The .sh.level variable can now only be changed within a DEBUG trap. When
  trap execution ends, the variable and the scope are now restored. These
  changes disallow an inconsistent shell scoping state causing instability.

2022-07-10:

- Fixed a potential crash on retrieving an empty line from the command history.

- Fixed a potential crash in the lexical analyser on processing single-byte
  characters with the highest bit set.

2022-07-09:

- Fixed a bug that broke '[[ ... ]]' test expressions for the command
  following a syntax error in an associative array assignment.

2022-07-05:

- Fixed a spurious syntax error on encountering a process substitution
  following a redirection without being an argument to a redirection.
  For example, this now writes 'OK' to standard error: cat >&2 <(echo OK)

- Fixed the detection of a syntax error in compound assignments to
  associative arrays.

2022-07-02:

- Fixed a bug where, if the last command in a subshell was an external
  command that was terminated by a signal, the exit status ($?) of the
  subshell did not reflect this by adding 256 to the signal number.

- Fixed a bug that caused signal traps to be ignored if the shell was
  signalled from a subshell that is the last command in the script.

2022-07-01:

- In scripts, $COLUMNS and $LINES are now kept up to date in scripts at
  initialization and when the window size changes (previously, this
  required setting a dummy trap for the SIGWINCH signal in the script).

2022-06-28:

- Fixed a bug that caused the <#((num)) or >#((num)) arithmetic seek
  redirection operator to fail if used with file descriptor 0, 1 or 2
  connected to a block device.

2022-06-22:

- Fixed: 'echo' failed when used inside a command substitution that
  is inside a nested compound assignment.

- Fixed a crash in KEYBD trap handling introduced on 2021-11-29.

2022-06-20:

- Fixed a race condition that could cause redirections to fail with a
  "cannot create" or "cannot open" error while processing a signal trap.

2022-06-18:

- Fixed a bug where, with the monitor or pipefail option on, the shell
  failed to wait for all component commands in a pipeline to terminate if
  the last component command was an external command and the pipeline was
  the last command in a background subshell.

- When any trap except DEBUG, KILL or STOP is set to a non-empty command,
  the last command in a script or forked subshell will no longer avoid forking
  before executing; this optimization incorrectly bypassed the traps.

2022-06-15:

- Fixed a bug where converting an indexed array into an associative array in
  a subshell failed, resulting in an empty associative array.

2022-06-13:

- Trapping a signal that is not a pseudosignal will now cause a virtual
  subshell to fork into a real one. This ensures a persistent PID where
  other processes can signal the subshell (the PID of a virtual subshell may
  change as other commands cause it to fork), and fixes a bug where a signal
  could not be correctly or effectively trapped in a subshell if the same
  signal was also trapped in the main shell environment.

2022-06-12:

- The 'time' keyword and 'times' built-in now display three digits after the
  decimal point by default; up to six remain configurable (see 2022-06-06).

- The POSIX mode now disables zero-padding of seconds in 'time'/'times' output.

2022-06-09:

- The POSIX mode has been amended to use a UNIX pipe(2) instead of a
  socketpair(2) to connect commands in a pipeline, as the standard requires.
  (When reading directly from a pipeline in posix mode, the <#pattern and
  <##pattern redirection operators will not work and the -n option to the
  read built-in will not return early when reading from a slow device.)

- An interactive shell initialized in POSIX mode now once again has the
  preset aliases defined. This amends a change made on 2020-09-11.

- If a long-form shell option name is abbreviated so it matches multiple
  options, the error message from ksh or 'set' now reads "ambiguous option".

2022-06-08:

- If -B/--braceexpand is turned on in --posix mode, it now only allows brace
  expansion on literal strings and not on the values of unquoted expansions.
  This behaviour is like bash and zsh, as well as compliant with a future
  version of the POSIX standard that may specify brace expansion:
  https://www.austingroupbugs.net/view.php?id=1193

2022-06-07:

- Fixed a bug in 'typeset' where compound variables could acquire a spurious
  -x (export) attribute when printing their values, triggering other bugs.

2022-06-06:

- The 'time' reserved word now displays seconds with six digits after the
  decimal point by default. Its TIMEFORMAT variable supports a new %C
  specifier that yields the the total number of CPU seconds, i.e. the sum
  of the time spent in user and system mode.

- The 'times' special built-in command now displays seconds with six digits
  after the decimal point.

2022-06-05:

- Fixed a bug where tab completion would spuriously execute a command
  substitution after entering: '`something<TAB> or generate a spurious
  'end of file unexpected' syntax error after entering: '$(something<TAB>.

- Fixed bug where tab completion stopped working for arguments following a
  quoted string with an escaped backslash in the form $'foo\'bar'.

2022-06-04:

- Added a new --functrace long-form shell option which causes the -x/--xtrace
  option's state and the DEBUG trap action to be inherited by function scopes
  instead of being reset to default. Changes made to them within a function
  scope still do not propagate back to the parent scope. Similarly, this
  option also causes the DEBUG trap action to be inherited by subshells.

2022-06-03:

- Fixed a couple of bugs that caused floating point variables imported from
  a parent ksh through the environment to be corrupted.

- Fixed a bug where invocation-local assignments preceding a built-in or
  external command or function call did not honour their pre-existing
  attributes set by typeset (such as -i or -F) in certain cases.

2022-06-01:

- New 'typeset' feature inspired by bash (and zsh and mksh): the -g flag
  causes the specified variable(s) to be created globally, ignoring the
  local scope of ksh functions or name spaces. For example, this allows
  creating a global array or numeric variable from a ksh function.
  Thanks to @ormaaj for the feature suggestion and to @hyenias for testing.

2022-05-29:

- Fixed a bug causing an inconsistent state after a special built-in command
  threw an error within a namespace.

2022-05-27:

- Fixed a bug introduced on 2022-03-05 where 'set --default', while turning
  off the --posix option, did not re-enable the special handling of a repeated
  $IFS whitespace character as non-whitespace.

2022-05-25:

- Fixed a bug introduced on 2021-02-20 that caused incorrect output for
  typeset -L/-R/-Z when the variable contained leading or trailing spaces.
  Thanks to George Lijo for the report and the fix.

2022-05-21:

- Fixed a bug, present since the beginning of ksh93, that broke backslash line
  continuation within $(standard) and ${ shared-state; } command substitutions.
  Thanks to atheik for the analysis and the fix. (BUG_CSUBLNCONT)

2022-05-20:

- Fixed an ancient bug that caused a spurious syntax error when using double
  quotes within a `backtick` command substitution within double quotes.
  Thanks to atheik for the analysis and the fix. (BUG_CSUBBTQUOT)

2022-03-10:

- Fixed another corner case bug in the 'test'/'[' command.

- A memory leak was fixed in the --man self-documentation options
  of built-in commands.

2022-03-05:

- The 'enum' command can now create more than one type per invocation.

- The POSIX compatibility mode has been amended to disable the special handling
  of a repeated $IFS whitespace character as non-whitespace.

2022-02-23:

- When reading input from the keyboard, ksh now turns off nonblocking I/O
  mode for standard input if a previously ran program left it on, so that
  interactive programs that expect it to be off work properly.

- Fixed a regression introduced on 2022-02-02 that caused interactive shells
  to enter an infinite loop when a command failed to execute on Linux
  systems with version 2.35 of glibc.

- Fixed a SIGTTOU lockup that could cause ksh to freeze under strace(1) after
  a command failed to execute in an interactive shell.

2022-02-18:

- Fixed a regression introduced on 2021-04-11 that caused the += operator in
  invocation-local assignments to crash the shell or modify variables outside
  of the invocation-local scope.

2022-02-17:

- Fixed a crash, introduced on 2021-01-19, that occurred when using 'cd' in
  a subshell with the PWD variable unset.

- Fixed a crash that could occur when or after entering the suspend character
  (Ctrl+Z) while the shell was blocked trying to write to a FIFO special file.

2022-02-16:

- Backported minor additions to the 'read' built-in command from ksh 93v-:
  '-a' is now the same as '-A' and '-u p' is the same as '-p'. This is for
  compatibility with some 93v- or ksh2020 scripts. (Note that their change
  to the '-p' option to support both prompts and coprocess reads was not
  backported because we found it to be broken and unfixable.)

2022-02-15:

- A bug was fixed in fast filescan loops (like 'while <file; do ...; done',
  enabled by default by the SHOPT_FILESCAN compile-time option) in which
  "$@" incorrectly acted like "$*" within the do...done block.

- Improved sanity check for filescan loops: they are now only recognised if
  'while' is followed by a single input redirection without any command
  name/arguments or variable assignments.

- As SHOPT_FILESCAN has been enabled by default since ksh 93l 2001-06-01,
  the fast filescan loop is now documented in the manual page and the
  compile-time option is no longer considered experimental.

- Filescan loops are now disabled at runtime if the --posix option is active
  as they break a portable use case: POSIXly, 'while <file; do stuff; done'
  repeatedly executes 'stuff' while 'file' can successfully be opened for
  reading, without actually reading from 'file'.

2022-02-12:

- In multibyte locales such as UTF-8, shell input is no longer corrupted when
  a KEYBD trap is active. However, the KEYBD trap is not yet multibyte ready
  and is now only triggered for ASCII characters (1-127) in a multibyte locale.

2022-02-11:

- On the interactive shell, tab/esc completion is no longer disabled as a side
  effect of turning off pathname expansion with 'set -f' or 'set -o noglob'.

- Fixed a bug in which a >&- or <&- redirection could persist past a
  subshell in certain corner cases involving 'exec' or 'redirect'.

2022-02-08:

- Multiple bugs were fixed in the method that ksh uses to execute a shell
  script without a #! path. Among other things, custom types and other
  changes in built-in commands will no longer affect the invoked script.
  The state of the 'posix' option is now inherited by the script.

- To avoid an inconsistent state, the 'enum' and 'typeset -T' commands are
  no longer allowed to replace special built-in commands. For instance,
  'enum trap=(a b c)' is now an error because 'trap' is a special built-in.
  The ability of 'typeset -T' to redefine a type is not affected.

- A command like 'typeset -T foo_t' without any assignment no longer creates
  an incompletely defined 'foo_t' built-in command that will crash the shell
  when used. Instead, it is now silently ignored for backwards compatibility.

- Compound arrays belonging to a type created with 'typeset -T' now have
  their -C attribute preserved in the output of 'typeset -p'.

- A bug has been fixed in which the 'typeset -p' output of a two-dimensional
  sparse indexed array would cause the second subscript to be treated as an
  associative array when read back in by the shell. Elements that are sparse
  indexed arrays are now prefixed with "typeset -a".

- The rewritten .sh.match code from ksh93v- has been backported to ksh93u+m,
  fixing many bugs and improving performance by a considerable amount.

2022-02-05:

- Fixed: for indexed arrays, given an unset array member a[i] with i > 0,
  ${a[i]=value} failed to assign the value and ${v[i]?error} failed to throw
  an error.

- Fixed: the -a/--allexport shell option incorrectly exported some variables
  with names containing a dot to the environment. Note that the '-x' typeset
  attribute may still be set for them, but this will now not have any
  effect. Variables created in namespaces declared with the 'namespace'
  keyword are only exported while their namespace is active.

2022-02-04:

- Fixed a bug in 'typeset -p': for an indexed array variable that is set
  but empty, it will no longer output a nonexistent '[0]=' element.

2022-02-02:

- Fixed the -a/allexport option to export all variables that are assigned
  values. Previously, arithmetic $((var=1)) or conditional ${var:=value}
  assignments were not exported even with allexport on.

- Fixed a memory leak that could occur when using traps.

- Fixed a use after free issue that could occur when modifying or setting
  a SIGCHLD trap.

2022-02-01:

- Upon invocation, the interactive shell no longer leaves the user without
  a line editor if the VISUAL or EDITOR variable does not indicate emacs,
  gmacs or vi; instead, it now turns on the emacs option by default.

2022-01-31:

- Improved keyboard support for the vi and emacs built-in line editors:
  - Added support for Home key sequences ^[[1~ and ^[[7~ as well as End key
    sequences ^[[4~ and ^[[8~.
  - Added support for arrow key sequences ^[OA, ^[OB, ^[OC and ^[OD.
  - Added support for the following keyboard shortcuts (if the platform
    supports the expected escape sequence):
    - Ctrl-Left Arrow:  Go back one word
    - Alt-Left Arrow:   Go back one word        (Not supported on Haiku)
    - Ctrl-Right Arrow: Go forward one word
    - Alt-Right Arrow:  Go forward one word     (Not supported on Haiku)
    - Ctrl-G:           Cancel reverse search
    - Ctrl-Delete:      Delete next word        (Not supported on Haiku)
  - Added a keybind for the Insert key, which differs in the emacs and vi
    editing modes:
    - In emacs mode, Insert escapes the next character.
    - In vi mode, Insert will switch the editor to insert mode (like in vim).

- Fixed a bug in SIGINT handling: if a script ran an external command that
  interrupted itself (and only itself, not the process group) with SIGINT,
  the script that ran the command was also interrupted.

2022-01-28:

- Fixed longstanding job control breakage that occurred on the interactive
  shell when suspending (Ctrl+Z) an external command invoked by a dot script
  or POSIX shell function, or via 'eval'.

- Fixed a memory leak that occurred when running a command that was found on
  the PATH.

2022-01-26:

- On Cygwin, ksh now executes scripts that do not have a #! path itself,
  like it does on other systems, instead of with /bin/sh.

- Fixed a spurious syntax error which occurred when attempting to use array
  subscript expansion with unset variables (i.e., ${foo[${bar}..${baz}]}).

2022-01-24:

- Fixed a crashing bug in history expansion that could occur when using the "&"
  modifier to repeat a substitution while there was no previous substitution.

- History expansion is now documented in the ksh(1) manual page.

- In history expansion, the history comment character '#' is now enabled by
  default, as it is on bash.

- In history expansion, the 'a' modifier is now a synonym for 'g', as on bash.

- Fixed a bug in history expansion where the 'p' modifier had no effect if
  the 'histverify' option is on.

2022-01-20:

- Disallow out-of-range event numbers in history expansion (-H/-o histexpand).
  Previously these were accepted, resulting in corrupted expansions.

- Fixed a potential crash in history expansion due to a buffer overflow.

2022-01-12:

- Added bash-inspired --histreedit and --histverify options that modify history
  expansion (--histexpand), allowing editing on failure or before execution.

2022-01-04:

- Fixed an issue in vi mode that caused tab completion to fail if the
  last character on the command line was a space.

2021-12-29:

- Fixed numerous build errors that prevented ksh from running on Haiku OS.

- Added support for the SIGKILLTHR signal on operating systems that
  implement it.

2021-12-28:

- Fixed a bug that caused CDPATH to continue working after unsetting it.

- Added three options to the ulimit builtin with the same names and
  functionality as in Bash:
  - 'ulimit -k' sets the maximum number of kqueues.
  - 'ulimit -P' sets the maximum number of pseudo-terminals.
  - 'ulimit -R' sets the maximum time in microseconds a real-time process
    can run before blocking.
  Note that to use these options the operating system must support the
  corresponding resource limit.

2021-12-27:

- Two bash-like flags for 'whence' were backported from ksh 93v-:
  - 'whence -P/type -P' is an alias to the existing -p flag.
  - 'whence -t/type -t' will print only the type of a command in a simple
    format that is designed to be easy to use for scripts. Example:
        $ type -t typeset; whence -t sh
        builtin
        file

- Fixed a crash or freeze that would occur on Linux when using Ctrl+C to
  interrupt a command substitution containing a pipe in an interactive shell.

- Fixed a crash that could occur while processing a here-document while
  xtrace (set -x) is on and the $PS4 prompt contains parameter expansions or
  command substitutions.

- The mkservice and eloop builtins can now be built by enabling the
  new SHOPT_MKSERVICE setting in src/cmd/ksh93/SHOPT.sh.

2021-12-26:

- Listing aliases or tracked aliases in a script no longer corrupts
  shcomp's generated bytecode.

- Listing specific aliases with 'alias -p' and specific tracked aliases
  with 'alias -pt' now works as documented. This means that the following
  string of commands now works as you would expect:
	$ hash -r; unalias -a
	$ alias foo=bar; hash cat
	$ alias -p foo; alias -pt cat
	alias foo=bar
	alias -t cat

- As a result of the above fix, listing all tracked aliases with 'alias -pt'
  now prints commands that can be reused to recreate the tracked aliases.

- Attempting to list a non-existent alias or tracked alias with the -p option
  now causes an error and sets the exit status to the number of non-existent
  aliases passed.

- Attempting to list 256 non-existent aliases now errors out with the exit
  status set to one.

2021-12-22:

- Process substitutions run in a profile script no longer print their
  process ID when run.

2021-12-21:

- Fixed a bug that caused subshells (such as code blocks in parentheses) to
  partially behave like the interactive main shell after running anything
  that invokes the parser. For example:
	$ (eval :; sleep 1 & echo done)
	[1]	30909      <--- incorrect job control output from subshell
	done

- Fixed: after suspending (Ctrl+Z) a subshell that is running an external
  command, resuming the subshell with 'fg' failed and the job was lost.
	$ (vi)    <--- press Ctrl+Z
	[2] + Stopped                  (vi)
	$ fg
	(vi)      <--- vi failed to resume; immediate return to command line
	$ fg
	ksh: no such job

2021-12-20:

- Ported performance optimizations from illumos to improve the performance
  of the cksum builtin. (Note that the cksum builtin is not enabled by
  default.)

2021-12-17:

- Ksh no longer behaves badly when parsing a type definition command
  ('typeset -T' or 'enum') without executing it or when executing it in
  a subshell. Types can now safely be defined in subshells and defined
  conditionally as in 'if condition; then enum ...; fi'.

- Single digits can now be compared lexically in [[ ... ]] with the
  < and > operators.

2021-12-16:

- Changed the default selection of compiled-in /opt/ast/bin built-in libcmd
  commands to: basename, cat, cp, cut, dirname, getconf, ln, mktemp, mv.
  Add /opt/ast/bin to your $PATH to use these. Type 'cp --man', etc. for info.

- A bug introduced on 2020-09-17 was fixed that caused interactive ksh to exit
  if Ctrl+C was pressed while SIGINT was being ignored (as in "trap '' INT").

2021-12-13:

- Fixed a bug introduced on 2020-08-09 that prevented '.' and '..' from
  being completed when using file name tab completion.

- Fixed a bug on illumos that caused the chown builtin to fail with 'Invalid
  argument' after failing to change the ownership of a file twice using an ID
  that doesn't exist in /etc/passwd. (Note that the chown builtin is not
  enabled by default.)

2021-12-11:

- Fixed two more crashing bugs that occurred if ksh received a signal (such
  as SIGINT due to Ctrl+C) while the user is entering a multi-line command
  substitution in an interactive shell.

- The shell linter's warning for variable expansion in ((...)) now tells the
  user which variable is causing performance degradation.

- The shell linter now warns the user x=$((expr)) is slower than ((x=expr))
  when assigning a value to a variable.

2021-12-09:

- Increased the general robustness of discipline function handling, fixing
  crashing bugs with PS2.get() and .sh.tilde.get() disciplines, among others.

- Fixed a crash that occurred on the interactive shell if the PS1 prompt
  contains multiple command substitutions and the user interrupts input
  while the shell is on a PS2 prompt waiting for the user to complete a
  command substitution of the form $( ... ).

2021-12-08:

- Fixed: if a function returned with a status > 256 using the 'return' command
  and the return value corresponded to a value that could have resulted from a
  signal, and an EXIT trap was active, then the shell mistakenly issued that
  signal to itself. Depending on the signal, this could cause the shell to
  terminate ungracefully, e.g. 'return 267' caused SIGSEGV ("memory fault").

- For the 'return' built-in command, you can now freely specify any
  return value that fits in a signed integer, typically a 32-bit value.
  Note that $? is truncated to 8 bits when the current (sub)shell exits.

- The head and tail builtins now correctly handle files that do not have an
  ending newline. (Note that the tail builtin is not compiled in by default.)

2021-12-05:

- Fixed an issue on illumos that caused some parameters in the getconf
  builtin to fail.

- The cd built-in command now supports a -e option (as specified in
  https://www.austingroupbugs.net/view.php?id=253). Passing -e alongside -P
  is used to guarantee the cd built-in returns with exit status 1 if the
  current working directory couldn't be determined after successfully changing
  the directory.

2021-12-01:

- Fixed a memory fault that occurred when a discipline function exited
  with an error from a special builtin or when a discipline function exited
  because of a signal.

2021-11-29:

- Fixed a memory fault that prevented ksh from functioning on ARM-based Macs.

- A bug that caused the time keyword to override the errexit shell option has
  been fixed.

- Fixed a crash that could occur when a KEYBD trap was set and a multi-line
  command substitution was input in an interactive shell.

- The shell linter's warnings for obsolete arithmetic operators in [[ ... ]]
  and unnecessary variable expansion in ((...)) have been improved.

2021-11-24:

- The --posix mode was amended to stop the '.' command (but not 'source') from
  looking up functions defined with the 'function' keyword. In the POSIX
  standard and on other shells, the '.' command finds only script files.

- The rm built-in's -d/--directory option has been fixed. It now properly
  removes empty directories and refuses to remove non-empty directories
  (as specified in https://www.austingroupbugs.net/view.php?id=802). Note
  that the rm built-in command isn't compiled in by default.

2021-11-23:

- A bug was fixed that allowed arithmetic expressions to assign out-of-range
  values to variables of an enumeration type defined with the 'enum' command,
  causing undefined behavior. Within arithmetic expressions, enumeration
  values translate to index numbers from 0 to the number of elements minus 1.
  That range is now checked for. Decimal fractions are ignored.

2021-11-21:

- It is now possible to use types defined by 'enum' in contexts where the
  script is entirely parsed before (or without) being executed, such as
  dotted/sourced scripts and scripts compiled by shcomp.

- Added support for the size mode to the stty(1) built-in. This mode is used
  to display the terminal's number of rows and columns. Note that the stty
  built-in is not compiled in by default. This can be changed by adding
  stty to the table of built-ins in src/cmd/ksh93/data/builtins.c.

2021-11-20:

- Listing types with 'typeset -T' no longer displays incomplete versions of
  types created by the enum built-in.

2021-11-18:

- The printf built-in command now supports a -v option as on bash and zsh.
  This allows you to assign formatted output directly to a variable.

- Fixed a performance regression introduced on 2021-05-03 that caused
  the shbench[*] fibonacci benchmark to run slower.
  [*]: https://github.com/ksh-community/shbench

2021-11-16:

- By default, arithmetic expressions in ksh no longer interpret a number
  with a leading zero as octal in any context. Use 8#octalnumber instead.
  Before, ksh would arbitrarily recognize the leading octal zero in some
  contexts but not others, e.g., both of:
	$ x=010; echo "$((x)), $(($x))"
	$ set -o letoctal; x=010; let y=$x z=010; echo "$y, $z"
  would output '10, 8'. These now output '10, 10' and '8, 8', respectively.
  Arithmetic expressions now also behave identically within and outside
  ((...)) and $((...)). Setting the --posix compliance option turns on the
  recognition of the leading octal zero for all arithmetic contexts.

2021-11-15:

- In arithmetic evaluation, the --posix compliance option now disables the
  special floating point constants Inf and NaN so that $((inf)) and $((nan))
  refer to the variables by those names as the standard requires. (BUG_ARITHNAN)

- Fixed two file descriptor leaks in the hist builtin that occurred when
  the -s flag ran a command or encountered an error.

2021-11-14:

- Fixed: ksh crashed after unsetting .sh.match and then matching a pattern.

- Another test/[ fix: "test \( string1 -a string2 \)" and "test \( string1 -o
  string2 \)" no longer give an incorrect "argument expected" error message.

2021-11-13:

- The test/[ built-in command now supports the '<' and '=~' operators from [[.
  As of now, test/[ supports the same operators as [[ except for the different
  and/or operators. Note: test/[ remains deprecated due to its many pitfalls.

- The test/[ built-in command is fixed so that the binary -a (and) and -o (or)
  operators, as in [ "$a" -a "$b" ] or [ "$a" -o "$b" ], work even if "$a" is
  '!' or '('. To avoid breaking backwards compatibility with the nonstandard
  unary [ -a "$file" ] and [ -o "$option" ] operators in combination with '!'
  or parentheses, this fix is only activated if the posix option is on.

2021-11-07:

- Fixed a bug that could corrupt output if standard output is closed upon
  initializing the shell.

- Improved BUG_PUTIOERR fix (2020-05-14) with more error checking. On
  systems with the "disk full" error testing device /dev/full, an
  echo/print/printf to /dev/full now always yields a non-zero exit status.

2021-09-13:

- Disable the POSIX arithmetic context while running a command substitution
  invoked from within an arithmetic expression. This fixes a bug that caused
  integer arguments with a leading zero to be incorrectly interpreted as octal
  numbers in non-POSIX arithmetic contexts within such command substitutions.

2021-09-12:

- When invoking a script without an interpreter/hashbang path on Linux and
  macOS, ksh can now update 'ps' output to show longer command lines.

2021-08-13:

- An issue was fixed that could cause old-style `backtick` command
  substitutions to hang in certain cases.

2021-06-03:

- Fixed a bug in the [[ compound command: the '!' logical negation operator
  now correctly negates another '!', e.g., [[ ! ! 1 -eq 1 ]] now returns
  0/true. Note that this has always been the case for 'test'/'['.

2021-05-18:

- Fixed SHLVL so that replacing ksh by itself (exec ksh) will not increase it.

- Fixed a regression introduced on 2020-08-05 that caused a non-interactive
  shell to exit if an I/O redirection of a function call encountered an error.

2021-05-13:

- Fixed a bug with 'test -t 1' that was introduced on 2021-04-26:
  v=$(test -t 1 >/dev/tty && echo ok) did not assign 'ok' to v.

2021-05-10:

- Release 1.0.0-beta.1.

2021-05-07:

- Backported three ksh 93v- math.tab changes, allowing for an exp10()
  arithmetic function if one exists in the C library, a new float()
  function, and lastly an updated int() function that rounds to zero
  instead of being an alias to floor().

2021-05-05:

- Fixed: a preceding variable assignment like foo=bar in 'foo=bar command'
  (with no command arguments after 'command') incorrectly survived the
  'command' regular built-in command invocation.

- Fixed: 'command -p some_utility' intermittently failed to find the utility
  under certain conditions due to a memory corruption issue.

2021-05-03:

- Subshells (even if non-forked) now keep a properly separated state of the
  pseudorandom generator used for $RANDOM, so that using $RANDOM in a
  non-forked subshell no longer influences a reproducible $RANDOM sequence in
  the parent environment. In addition, upon invoking a subshell, $RANDOM is now
  reseeded (as mksh and bash do).

- Fixed program flow corruption that occurred in scripts on executing a
  background job in a nested subshell, as in ( ( simple_command & ) ).

- Completed the 2021-04-30 fix for ${var<OP>'{}'} where <OP> is '-', '+',
  ':-' or ':+' by fixing a bug that caused an extra '}' to be output.

- Following the resolution of Austin Group bug 1393[*] that is set to be
  included in the next version of the POSIX standard, the 'command' prefix
  in POSIX mode (set -o posix) no longer disables the declaration properties
  of declaration built-ins. This reverts a change introduced on 2020-09-11.
  [*] https://austingroupbugs.net/view.php?id=1393

- Fixed arithmetic assignment operations for multidimensional indexed arrays.

2021-04-30:

- The emacs 'ESC .' (M-.) and vi '_' commands now take shell quoting into
  account when repeating a word from the previous command line. For example, if
  the previous command is 'ls Stairway\ To\ Heaven.mp3', then they now insert
  'Stairway\ To\ Heaven.mp3' instead of 'Heaven.mp3'. Thanks to Govind Kamat.

- Fixed a bug introduced on 2020-09-05 that caused "echo ${var:+'{}'}"
  to be misparsed.

- Fixed: the effects of 'builtin', 'exec' and 'ulimit' leaked out of a parent
  virtual subshell if run from a ${ shared-state; } command substitution.

2021-04-26:

- Fixed a bug introduced on 2021-02-20 in which a shared-state command
  substitution stopped sharing its state with the calling shell environment
  if it executed a command that locally redirected standard output.

2021-04-22:

- shcomp (the shell bytecode compiler) was fixed to correctly compile process
  substitutions used as the file name to a redirection, as in 'cmd < <(cmd)'.

- Fixed a bug introduced on 2020-07-13 that set LINENO to the wrong line
  number after leaving a virtual subshell in which LINENO had been unset.

2021-04-21:

- Fixed a bug introduced on 2020-09-28 that caused an interactive ksh to exit
  if a profile script (such as ~/.kshrc) contains a syntax error.

2021-04-20:

- Fixed three problems with the /opt/ast/bin/getconf built-in command:
  1. The -l/--lowercase option did not change all variable names to lower case.
  2. The -q/--quote option now quotes all string values. Previously, it only
     quoted string values that had a space or other non-shellsafe character.
  3. The -c/--call, -n/--name and -s/--standard options matched all variable
     names provided by 'getconf -a', even if none were actual matches.

- The readonly attribute of ksh variables is no longer imported from
  or exported to other ksh shell instances through the environment.

2021-04-16:

- Fixed a bug in emacs mode: after using tab completion to complete the name
  of a directory, it was not possible to type numbers after the slash.

- Fixed an optimization bug that caused the <>; redirection operator to fail
  when used with the last command in a -c script.

2021-04-14:

- Path-bound built-ins (such as /opt/ast/bin/cat) can now be executed by
  invoking the canonical path, so the following will now work as expected:
	$ /opt/ast/bin/cat --version
	  version         cat (AT&T Research) 2012-05-31
	$ (PATH=/opt/ast/bin:$PATH; "$(whence -p cat)" --version)
	  version         cat (AT&T Research) 2012-05-31
  Non-canonical paths such as /opt/ast/./bin/cat will not find the built-ins.

- Path-bound built-ins will now also be found on a PATH set locally using an
  assignment preceding the command, so the following will now work as expected:
	$ PATH=/opt/ast/bin cat --version
	  version         cat (AT&T Research) 2012-05-31

2021-04-13:

- Fixed a few bugs that could cause ksh to show the wrong error message and/or
  return the wrong exit status if a command couldn't be executed. In
  scenarios where the command was found in the PATH but it was not executable,
  ksh now returns with exit status 126. Otherwise, ksh will return with exit
  status 127 (such as if the command isn't found or if the command name is
  too long).

2021-04-12:

- Corrected a memory fault when an attempt was made to unset the default
  nameref KSH_VERSION from the shell environment prior to any other name
  reference variable creation or modification.

2021-04-11:

- Fixed two related regressions introduced on 2020-06-16:
  1. The += assignment failed to append the value of variables when used
     in an invocation-local scope. The following should print '5', but
     the regression resulted in '3' being printed instead:
       $ integer foo=2; foo+=3 command eval 'echo $foo'
       3
  2. Any += assignment used in an invocation-local scope could modify
     readonly variables.

2021-04-10:

- Fixed: the internal count of the recursion level for arithmetic expressions
  was not reset when certain errors occurred in a virtual subshell. This could
  cause an erroneous "recursion to deep" error when a loop executed many
  subshells containing arithmetic expressions with errors, e.g. for testing.

2021-04-09:

- Fixed a bug that caused ksh to enable -c during the shell's initialization
  if the only argument passed was --posix.

- Fixed a related bug that caused 'set --posix' to leave the braceexpand and
  letoctal shell options unchanged.

- Fixed a bug that caused 'set --default' to unset the restricted option
  in restricted shells.

2021-04-08:

- Path-bound builtins will now be used by restricted shells if /opt/ast/bin
  is in the $PATH upon invoking the shell or before setting it to restricted.

- Fixed a bug that caused "printf '%T\n' now" to ignore $LC_ALL and $LC_TIME
  if the current locale was previously set, unset then set again.

2021-04-07:

- The $LC_TIME variable is now recognized by ksh and if set to an invalid
  locale will show an error.

- Fixed BUG_CSUBSTDO: If standard output is closed before running a command
  substitution, redirecting any other file descriptor no longer closes standard
  output inside of the command substitution.

2021-04-05:

- Fixed a regression, introduced in ksh 93t+ 2009-07-31, that caused a command
  like 'unset arr[3]' to unset not just element 3 of the array but all elements
  starting from 3, if a range expansion like ${arr[5..10]} was previously used.

- Several fixes for arrays of a type created by 'enum' were backported from ksh
  93v-, further to the two enum array fixes already applied on 2021-02-01:
  1. The array[@]} expansion was fixed for associative arrays of an enum type.
  2. Assignments now work correctly for all enum values for both indexed and
     associative arrays.
  3. 'unset' will now completely unset an associative array of an enum type.

2021-04-04:

- A bug was fixed that caused a broken prompt display upon redrawing the
  command line if the last line of the prompt includes an xterm escape
  sequence that is terminated by $'\a' (the bell character).

- Harden readonly variables. Readonly variables or arrays no longer allow
  attribute changes which would otherwise allow their value to be altered.
  Expanded support for readonly variables within multidimensional arrays.

2021-04-03:

- Fixed a bug that caused the uname builtin's -d option to change the output
  of the -o option.

- Fixed a possible crash that could occur when showing the domain name
  with the uname builtin's -d option.

2021-03-31:

- Fixed a bug that caused 'cd -' to ignore the current value of $OLDPWD
  when it's set to a different directory in a new scope.

- Fixed a related bug that caused ksh to use the wrong value for $PWD
  when in a new scope.

2021-03-29:

- Fixed an intermittent crash that could occur in vi mode when using the 'b'
  or 'B' commands to go back one word.

2021-03-27:

- The 'test' builtin will now show an error message when given the invalid ']]'
  or '=~' operators; it also properly returns with exit status 2 now (instead
  of exit status 1). If the invalid operator is supported by [[ ... ]] (such
  as '=~'), test will now suggest the usage of [[ ... ]] instead.

2021-03-22:

- A new --globcasedetect shell option is added to ksh on OSs where we can check
  for a case-insensitive file system (currently macOS, Windows/Cygwin, Linux
  and QNX 7.0+). When this option is turned on, file name generation
  (globbing), as well as file name tab completion on interactive shells,
  automatically become case-insensitive on file systems where the difference
  between upper- and lowercase is ignored for file names. This is transparently
  determined for each directory, so a path pattern that spans multiple file
  systems can be part case-sensitive and part case-insensitive.
      The option is not compiled into ksh on systems where we do not know of a
  method to check for file system case insensitivity. The shell option can be
  force-compiled by setting SHOPT_GLOBCASEDET to 1 in src/cmd/ksh93/SHOPT.sh,
  but it won't have any effect on non-supported systems, so this is not
  recommended. It can be removed from ksh by setting SHOPT_GLOBCASEDET to 0.

2021-03-17:

- Fixed a bug with file name completion on the interactive shell in multibyte
  locales. Upon encountering two filenames with multibyte characters starting
  with the same byte, a partial multibyte character was autocompleted.

2021-03-16:

- Tilde expansion can now be extended or modified by defining a .sh.tilde.get
  or .sh.tilde.set discipline function. This replaces a 2004 undocumented
  attempt to add this functionality via a .sh.tilde built-in, which never
  worked and crashed the shell. See the manual for details on the new method.

- Fixed a bug in interactive shells: if a variable used by the shell called
  a discipline function (such as PS1.get() or COLUMNS.set()), the value of $?
  was set to the exit status of the discipline function instead of the last
  command run.

2021-03-15:

- If the HOME variable is unset, the bare tilde ~ now expands to the current
  user's system-configured home directory instead of merely the username.

- Tighten up potential invalid typeset attribute combos when more than
  one numeric type has been requested. In particular, -F and -i are no
  longer masked over by previously given float types.

2021-03-13:

- Fixed a file descriptor leak that occurred when ksh used /dev/fd for
  process substitutions passed to functions.

- Fixed a separate file descriptor leak that happened when a process
  substitution was passed to a nonexistent command.

2021-03-11:

- Fixed an intermittent bug that caused process substitutions to infinitely
  loop in Linux virtual machines that use systemd.

- Fixed a bug that caused process substitutions to leave lingering processes
  if the command invoking them never reads from them.

2021-03-09:

- The ${!foo@} and ${!foo*} expansions yield variable names beginning with foo,
  but excluded 'foo' itself. The fix for this is now backported from 93v- beta.

- test -v var, [ -v var ], and [[ -v var ]] did not correctly test if a
  variable is set or unset after it has been given a numeric attribute with
  'typeset' but not yet assigned a value. This has been fixed so that
  [[ -v var ]] is now equivalent to [[ -n ${var+set} ]] as documented.

2021-03-07:

- Fixed the typeset -p display of short integers without an assigned value.
  Also, the last -s or -l attribute option supplied for an integer is used.

- Fixed a bug with -G/--globstar introduced on 2020-08-09: patterns did not
  match anything if any pathname component was '.' or '..', e.g. '**/./glob.c'
  never matched. The 2020-08-09 fix does still apply to patterns like '.*'.

- Enhancement to -G/--globstar: symbolic links to directories are now followed
  if they match a normal (non-**) glob pattern. For example, if '/lnk' is a
  symlink to a directory, '/lnk/**' and '/l?k/**' now work as you would expect.

- Fixed a bug introduced on 2021-02-11 that caused job control on interactive
  ksh sessions to misbehave if the login shell was replaced by ksh using 'exec'.

2021-03-06:

- Fixed an old expansion bug: expansions of type ${var=value} and ${var:=value}
  did not perform an assignment and yielded the value 0 if 'var' was typeset as
  numeric (integer or float) but had not yet been assigned a value.

- Fixed a bug introduced on 2020-08-19: Ctrl+D would break after an
  interactive shell received SIGWINCH.

- Fixed a bug introduced on 2020-05-21: on an interactive shell, command lines
  containing a syntax error were not added to the command history file and
  sometimes corrupted the command history.

2021-03-05:

- Unbalanced quotes and backticks now correctly produce a syntax error
  in -c scripts, 'eval', and backtick-style command substitutions.

2021-03-04:

- Fixed an arbitrary command execution vulnerability that occurred when
  parsing the subscripts of arrays within arithmetic commands and expansion.

2021-03-01:

- Fixed the retention of size attributes when 'readonly' or 'typeset -r'
  was applied to an existing variable.

2021-02-26:

- Fixed three long-standing bugs with tab completion in the emacs editor:

  1. The editor accepted literal tabs without escaping in certain cases,
     causing buggy and inconsistent completion behaviour. Details:
     https://github.com/ksh93/ksh/issues/71#issuecomment-656970959
     https://github.com/ksh93/ksh/issues/71#issuecomment-657216472
     To enter a literal tab in emacs, you need to escape it with ^V or \.

  2. After completing a filename by choosing from a file completion menu,
     the terminal cursor was placed one position too far to the right,
     corrupting command line display. This happened with multiline active.
     Details: https://github.com/ksh93/ksh/issues/71#issue-655093805

  3. A completion menu was displayed if the file name to be completed was
     at the point where the rest of it started with a number, even if that
     part uniquely identified it so the menu only showed one item. Details:
     https://www.mail-archive.com/ast-users@lists.research.att.com/msg00436.html

- A bug with ${.sh.fun} in combination with the DEBUG trap has been fixed.
  The ${.sh.fun} variable wrongly continued to contain the name of the last
  function executed by the DEBUG trap after the trap action completed.

2021-02-21:

- Fixed: The way that SIGWINCH was handled (i.e. the signal emitted when the
  terminal window size changes) could cause strange emacs/vi editor behaviour.

2021-02-20:

- Fixed a bug introduced on 2021-01-20: if a DEBUG trap action yielded exit
  status 2, the execution of the next command was not skipped as documented.

- Fixed multiple buffer overflows causing crashes in typeset -L/-R-/-Z.

- Fixed typeset -Z zero-filling: if the number was zero, all zeros
  were skipped when changing the initial size value of the -Z attribute,
  leaving an empty string.

2021-02-18:

- A bug was fixed in the 'read' builtin that caused it to fail to process
  multibyte characters properly in Shift-JIS locales.

2021-02-17:

- Emacs mode fixes:
  1. Erasing a backslash while doing a reverse search (^R) no longer deletes
     extra characters.
  2. The backslash now escapes a subsequent interrupt (^C) as documented.

- Fixed a longstanding bug with shared-state command substitutions of the form
  ${ command; }. If these were executed in a subshell, changes made within
  could survive not only the command substitution but also the parent subshell.

2021-02-15:

- Fixed a regression introduced by ksh93 (was not in ksh88): an empty 'case'
  list on a single line ('case x in esac') was a syntax error.

- Fixed a bug in the emacs built-in editor, introduced on 2020-09-17, that
  made the Meta-D and Meta-H keys delete single characters instead of words.

- A new 'backslashctrl' shell option has been added. It is on by default.
  Turning it off (set +o backslashctrl or set --nobackslashctrl) disables the
  special escaping behaviour of the backslash character in the emacs and vi
  built-in editors. Particularly in the emacs editor, this makes it much easier
  to go back, insert a forgotten backslash into a command, and then continue
  editing without having your next cursor key replace your backslash with
  garbage. Note that Ctrl+V (or whatever other character was set using
  'stty lnext') always escapes all control characters in either editing mode.

2021-02-14:

- Due to a deficiency in some UNIX variants, the 'sleep' built-in command could
  occasionally sleep for slightly less than the time specified. It now performs
  an additional check against the system clock to make sure it sleeps at least
  the given amount of time. Thanks to Lev Kujawski for adding this feature.

- A few bugs were fixed that 93u+m introduced along with the new '-o posix'
  shell option on 2020-09-01:
  1. 'set --posix' now works as the expected equivalent of 'set -o posix'.
  2. As of 2020-09-18, the posix option turns off braceexpand and turns on
     letoctal. Any attempt to override that in a single command such as
     'set -o posix +o letoctal' was quietly ignored. This now works as long
     as the overriding option follows the posix option on the command line.
  3. The --default option to 'set' now stops the 'posix' option, if set or
     unset in the same 'set' command, from changing other options. This allows
     the command output by 'set +o' to correctly restore the current options.

2021-02-11:

- Fixed a bug that caused ksh to lose track of all running background jobs if
  a shared-state command substitution of the form v=${ cmd; } was used twice.

- Job control (the -m/-o monitor option) has been fixed for scripts. Background
  jobs are now correctly assigned their own process group when run from
  subshells (except command substitutions). The 'fg' command now also works for
  scripts as it does on other shells, though 'wait' should be preferred.

2021-02-05:

- Fixed a longstanding bug that caused redirections that store a file
  descriptor > 10 in a variable, such as {var}>file, to stop working if
  brace expansion (the -B or -o braceexpand option) was turned off. (Note
  that '{var}' is not a brace expansion as it does not contain ',' or '..'.)

2021-02-04:

- Fixed ksh crashing if an autoloaded function tried to autoload itself.
  ksh now errors out gracefully with an "autoload loop" error message.

- Fixed crash on trying a very long nonexistent command.

2021-02-01:

- Fixed a bug in 'typeset': the '-s' modifier option for short integer will
  now only be applied if the integer option '-i' is also present, avoiding
  inconsistent results and a crash.
  
- Fixed: scalar arrays (-a) and associative arrays (-A) of a type created by
  'enum' allowed values not specified by the enum type, corrupting results.

- Fixed: the "${array[@]}" expansion for associative arrays of a type created
  by 'enum' expanded to random numbers instead of the array's values.

2021-01-30:

- The -x option to the 'command' built-in now causes it to bypass built-ins
  so that it always runs/queries an external command. See 'command --man'.

- Fixed a bug in 'command -x' that caused the minimum exit status to be 1 if
  a command with many arguments was divided into several command invocations.

- The 2020-08-16 fix is improved with a compile-time feature test that
  detects if the OS requires extra bytes per argument in the arguments list,
  maximising the efficiency of 'command -x' for the system it runs on.

2021-01-24:

- Fixed a bug in 'typeset': combining the -u option with -F or -E caused the
  variable to become a hexadecimal floating point in error.

- Fixed: an unquoted variable expansion evaluated in a DEBUG trap action caused
  IFS field splitting to be deactivated in code executed after the trap action.
  This bug was introduced in ksh 93t+ 2009-11-30.

2021-01-23:

- Fixed: when the DEBUG trap was redefined in a subshell, the DEBUG trap in
  the parent environment was corrupted or the shell crashed.
  When a redirection was used in a DEBUG trap action, the trap was disabled.
  DEBUG traps were also incorrectly inherited by subshells and ksh functions.
  All this was caused by a bug introduced in ksh 93t 2008-06-24.

2021-01-22:

- Compile-time shell options can now be edited in src/cmd/ksh93/SHOPT.sh
  before building.

2021-01-20:

- Fixed: executing a DEBUG trap in a command substitution had side effects
  on the exit status ($?) of non-trap commands.
  This bug was introduced in ksh 93t 2008-09-21.

- The typeset builtin command now gives an informative error message if an
  incompatible combination of options is given.

2021-01-19:

- Fixed a crash when using 'cd' in a virtual/non-forking subshell in a
  situation where the current working directory cannot be determined.

2021-01-08:

- Fixed a crash on exceeding the maximum size of the $PS1 prompt.
  The maximum size is also increased from 160 to 256 bytes.

2021-01-07:

- Fixed a crash that could occur while ksh updated ${.sh.match}.

- Any changes to the hash table (a.k.a. "tracked aliases", i.e. cached $PATH
  searches) in a subshell now no longer affect the parent shell's hash table.

2021-01-05:

- Fixed a bug in 'cd' that caused 'cd ./foo' to search for 'foo' in $CDPATH.

2021-01-03:

- The invocation
	$ ksh +s
  caused an infinite loop and corrupted ~/.sh_history. This is now fixed so
  that the '-s' option is automatically turned on if there are no non-option
  command arguments, as documented in Bolsky & Korn (1995), p. 261.

2020-10-22:

- Fixed: 'typeset -F0', 'typeset -E0', and 'typeset -X0' floating point
  numerics having a precision of 0 with variable assignment.
  'typeset -F0 x; x=4.56' worked but not 'typeset -F0 x=4.56'.

2020-10-21:

- Fixed: More concisely correct the exporting of uppercase and lowercase
  variables when only the export and change case attributes were applied.
  This fix improves upon the previous 2020-09-30 modifications.

2020-10-06:

- The security of virtual/non-forking subshells that locally change the present
  working directory (PWD) using 'cd' has been improved in two ways.
  1. On entering a subshell, if the parent shell's PWD proves inaccessible upon
     saving it, the subshell will now fork into a separate process so the
     parent process never changes its PWD, avoiding the need to restore it.
  2. If some attack renders the parent shell's PWD unrestorable *after* ksh
     enters a virtual subshell, ksh will now error out on exiting it, as
     continuing would mean running arbitrary commands in the wrong PWD.
  Hopefully this is an acceptable compromise between performance and security.
  The proper fix would be to always fork a subshell when changing the working
  directory within it, but the resulting slowdown would likely be unpopular.

2020-09-30:

- Fixed: 'typeset -xu' and 'typeset -xl' (export + change case) failed to
  change the case of a variable's value in certain conditions.

- A ksh 93u+ regression was fixed in the combination of ERR trap handling and
  the 'pipefail' option. A pipeline now triggers the ERR trap correctly again
  if the 'pipefail' option is active and any of the pipeline elements return a
  nonzero exit status. Similarly, if both the 'errexit' and 'pipefail' options
  are active, ksh now correctly exits if any pipeline element returns nonzero.

- Autoloading a function no longer causes the calling script's $LINENO to be
  off by the number of lines in the function definition file that was loaded.
  This also corrects line numbers in warnings and error messages.

2020-09-28:

- While executing a ksh-style function, ksh 93u+ ignored all signals for which
  the function had not set a local trap, except for SIGINT and SIGQUIT. This
  was contrary to the manual, which states that a "trap condition that is not
  caught or ignored by the function causes the function to terminate and the
  condition to be passed on to the caller". This has now been fixed in 93u+m to
  match the documentation, so that e.g. global traps work as expected again.

2020-09-27:

- The shell's lexical analysis of a 'case' statement within a do...done block
  within a command substitution of the form $(...) has been fixed so that code
  like the following no longer throws a spurious syntax error:
	x=$(for i in 1; do case $i in word) true;; esac; done)
  Previously, this required a leading parenthesis before 'word', although the
  syntax error claimed that the ';;' was unexpected.

2020-09-26:

- 'whence -f' now completely ignores the existence of functions, as documented.

- ksh now does not import environment variables whose names are not valid in
  the shell language, as it would be impossible to change or unset them.
  However, they stay in the environment to be passed to child processes.

2020-09-25:

- whence -v/-a now reports the path to the file that an "undefined" (i.e.
  autoloadable) function will be loaded from when invoked, if found in $FPATH.

- When ksh invoked a shell script that does not have a leading
  #!/hashbang/path, 'ps' and /proc/<PID>/cmdline showed corrupted output if
  the new script's command line was shorter than that of the invoking script.
  This has been fixed by wiping the arguments buffer correctly.

2020-09-24:

- An omission made it impossible to turn off brace expansion within command
  substitutions (`...`, $(...) or ${ ...; }) as the code for parsing these
  did not check the -B/braceexpand option. This check has now been added.

2020-09-23:

- Fixed a crash that could occur when running a pipeline containing
  backtick-style command substitutions with job control enabled.

- Fixed a crash that occurred when using 'typeset -u' or 'typeset -l' on a
  special variable such as PATH, ENV or SHELL.

2020-09-21:

- A bug was fixed that caused command substitutions embedded in here-documents
  to lose the output of the commands they ran. This bug occurred when ksh was
  compiled with the SHOPT_SPAWN compile-time option.

- Bugfix: var=$(< file) now reads the file even if the standard input, standard
  output and/or standard error file descriptors are closed.

2020-09-20:

- Bugfix: when whence -v/-a found an "undefined" (i.e. autoloadable) function
  in $FPATH, it actually loaded the function as a side effect of reporting on
  its existence. Now it only reports, as documented.

- 'whence' will now canonicalise paths properly, resolving '.' and '..'
  elements in paths given to it. It also no longer prefixes a spurious
  double slash when doing something like 'cd / && whence bin/echo'.

2020-09-18:

- Setting the 'posix' option now turns off the 'braceexpand' option, as brace
  expansion is not specified by POSIX and potentially incompatible with sh
  scripts. In addition, 'set -o posix' now turns on the 'letoctal' option
  instead of controlling that behaviour directly. 'set +o posix' does the
  reverse of these.

2020-09-17:

- In the vi and emacs line editors, repeat count parameters can now also be
  used for the arrow keys and the forward-delete key. E.g., in emacs mode,
  <ESC> 7 <left-arrow> will now move the cursor seven positions to the left.
  In vi control mode, this would be entered as: 7 <left-arrow>.

- When a background job on an interactive shell received SIGINT or SIGPIPE, the
  job termination message was empty. It now shows "Interrupt" or "Broken Pipe".

- The -m (-o monitor) option is no longer ignored when specified on the shell
  invocation command line.

- A script that is interrupted with Ctrl+C now terminates its background jobs
  as expected, unless the -m (-o monitor) option was turned on.

2020-09-14:

- Corrected rounding of floating point values by ksh's printf %f formatting
  operator. Fix contributed by @hyenias.

- The forward-delete key now works as expected in emacs and vi editing modes.

2020-09-11:

- The 'command' regular builtin utility (which runs a simple command, removing
  special properties) has been made fully POSIX compliant.
  1. The 'command' name can now result from an expansion (fixing BUG_CMDEXPAN),
     e.g. 'c=command; "$c" ls' and 'set -- command ls; "$@"' now work.
  2. If and only if the POSIX mode (the new -o posix shell option) is active,
     then the 'command' utility now disables not only "special" but also
     "declaration" properties of builtin commands that it invokes, meaning:
     a. arguments that start with a variable name followed by '=' are
	always treated as regular words subject to normal shell syntax;
     b. 'command' can now stop the shell from exiting if a command that it
	invokes tries to modify a readonly variable (fixing BUG_CMDSPEXIT).

- The 'history' (== 'hist -l') and 'r' (== 'hist -s') interactive shell
  history commands have reverted to preset aliases and are now only loaded if
  the shell is interactive and not initialised in POSIX mode. This avoids
  unneeded conflicts with external commands by these names, particularly 'r'.

2020-09-09:

- Fixed BUG_LOOPRET2 and related bugs. The 'exit' and 'return' commands without
  an argument now correctly default to passing down the exit status of the
  last-run command. Tests like the following, in which the last-run command is
  'false', now correctly output 1 instead of 0:
	fn() { return || true; }; false; fn; echo "$?"
	fn() { while return; do true; done; }; false; fn; echo "$?"
	fn() { for i in 1; do return; done; }; false; fn; echo "$?"
	fn() { case 1 in 1) return ;; esac; }; false; fn; echo "$?"
	fn() { { return; } 2>&1; }; false; fn; echo "$?"

2020-09-05:

- Fixed erroneous syntax errors in parameter expansions such as ${var:-wor)d}
  or ${var+w(ord}. The parentheses now correctly lose their normal grammatical
  meaning within the braces. Fix by Eric Scrivner backported from ksh2020.

2020-09-04:

- Fixed a bug that caused a syntax error to be thrown if the special parameter
  expansions ${!} and ${$} (including braces) were used within a here-document.
  Bug reported by @Saikiran-m on GitHub.

2020-09-01:

- The bash-style '&>file' redirection shorthand (for '>file 2>&1') is now
  always recognised and not only when running rc/profile init scripts. It no
  longer issues a warning. This brings ksh93 in line with mksh, bash and zsh.

- A long-form shell option '-o posix' has been added, which implements a
  mode for better compatibility with the POSIX standard. It is automatically
  turned on if ksh is invoked under the name 'sh'.
  For now, it:
  * disables the &> redirection shorthand
  * causes the 'let' arithmetic command to recognise octal numbers by
    leading zeros regardless of the setting of the 'letoctal' option
  * causes file descriptors > 2 to be left open when invoking another program
  * makes the <> redirection operator default to stdin instead of stdout
    (this keeps the 2020-05-13 BUG_REDIRIO fix for the POSIX mode while
    restoring traditional ksh93 behaviour for backwards compatibility)
  * disables a noncompliant 'test -t' == 'test -t 1' compatibility hack
  * disables passing an exported variable's attributes (such as integer or
    readonly) to a new ksh process through the environment

2020-08-19:

- Sped up the 'read' command on most systems by 15-25%. Fixed a hanging bug
  on reading from a FIFO that could occur on macOS.

2020-08-17:

- 'command -p' incorrectly used the hash table entry (a.k.a. tracked alias)
  for a command if its path was previously hashed. It has now been fixed so
  it never consults the hash table.

2020-08-16:

- Fixed 'command -x' on macOS, Linux and Solaris by accounting for a 16-byte
  argument alignment. If execution does fail, it now aborts with an internal
  error message instead of entering an infinite retry loop.

2020-08-13:

- Fixed memory leaks and a crashing bug that occurred when defining and
  running functions in subshells.

2020-08-11:

- Fixed an intermittent crash upon running a large number of subshells.

2020-08-10:

- A number of fixes have been applied to the printf formatting directives
  %H and %#H (as well as the undocumented equivalents %(html)q and %(url)q):
  1. Both formatters have been made multibyte/UTF-8 aware, and no longer
     delete multibyte characters. Invalid UTF-8 byte sequences are rendered
     as ASCII question marks.
  2. %H no longer wrongly changes spaces to non-breaking spaces (&nbsp;).
  3. %H now converts the single quote (') to '%#39;' instead of '&apos;'
     which is not a valid entity in all HTML versions.
  4. %#H failed to encode some reserved characters (e.g. '?') while encoding
     some unreserved ones (e.g. '~'). It now percent-encodes all characters
     except those 'unreserved' as per RFC3986 (ASCII alphanumeric plus -._~).

- Fixed a crash that occurred intermittently after running an external
  command from a command substitution expanded from the $PS1 shell prompt.

2020-08-09:

- File name generation (a.k.a. pathname expansion, a.k.a. globbing) now
  never matches the special navigational names '.' (current directory) and
  '..' (parent directory). This change makes a pattern like .* useful; it
  now matches all hidden files (dotfiles) in the current directory, without
  the harmful inclusion of '.' and '..'.

2020-08-08:

- Argument checking in the 'redirect' builtin command (see 2020-06-11) has
  been improved to error out before executing redirections. For example, an
  error like 'redirect ls >foo.txt' now will not create 'foo.txt' and will
  not leave your standard output permanently redirected to it.

2020-08-06:

- Added the '${.sh.pid}' variable as an alternative to Bash's '$BASHPID'.
  This variable is set to the current shell's PID, unlike '$$' (which is
  set to the main shell's PID). In virtual subshells '${.sh.pid}' is not
  changed from its previous value, while in forked subshells '${.sh.pid}'
  is set to the subshell's process ID.

2020-08-05:

- Fixed a bug in functions that caused ksh to crash when an array with an
  unset method was turned into a multidimensional array.

- Fixed a bug that caused scripts to continue running after over-shifting
  in a function when the function call had a redirection.

- When generating shellquoted strings (such as with 'printf %q'), the
  hexadecimal value of a quoted unprintable character was not protected with
  square braces, e.g. 0x12 followed by '3' would be quoted as '\x123', which
  is a different value. Such strings are now quoted like '\x[12]3' if the
  next character is a hexadecimal digit.

2020-07-31:

- Fixed a bug that caused multidimensional associative arrays to be created
  with an extra array member.

- Fixed a bug that caused the expansions of positional parameters $1 - $9,
  as well as special parameters such as $? and $-, to corrupt any multibyte
  characters immediately following the expansion if a UTF-8 locale is active.

2020-07-29:

- On a ksh compiled to use fork(2) to run external commands, a bug has been
  fixed that caused signals (such as SIGINT, Ctrl+C) to be ignored within a
  non-forked subshell after running an external command within that subshell.

2020-07-25:

- Fixed BUG_MULTIBIFS: Multibyte characters can now be used as IFS
  delimiters. "$*" was incorrectly joining positional parameters on
  the first byte of a multibyte character. This was due to truncation
  based on the incorrect assumption the IFS would never be larger
  than a single byte.

- Fixed a bug that caused the sleep builtin to continue after being given
  an unrecognized option. 'sleep -: 1' will now show a usage message and
  exit instead of sleep for one second.

- Fixed a bug that caused the 'typeset' variable attributes -a, -A, -l, and
  -u to leak out of a subshell if they were set without assigning a value.

2020-07-23:

- Fixed an infinite loop that could occur when ksh is the system's /bin/sh.

- A command substitution that is run on the same line as a here-document
  will no longer cause a syntax error.

2020-07-22:

- Fixed two race conditions when running external commands on
  interactive shells with job control active.

2020-07-20:

- If a shell function and a built-in command by the same name exist,
  'whence -a' and 'type -a' now report both.

- Fixed a bug that caused file descriptors opened with 'redirect' or 'exec'
  to survive a subshell environment after exiting it.

2020-07-19:

- Fixed a crash that occurred in the '.' command when using kshdb.

- Fixed a crash that occurred when attempting to use redirection with an
  invalid file descriptor.

2020-07-16:

- The 'history' and 'r' default aliases have been made regular built-ins,
  leaving zero default aliases.

- Fixed a bug that caused 'sleep -s' to have no effect with intervals longer
  than 30 seconds.

- The accuracy of the sleep builtin has been improved. It no longer ignores
  microseconds and doesn't add extra milliseconds when the interval is less
  than 31 seconds.

2020-07-15:

- The 'autoload', 'compound', 'float', 'functions', 'integer' and 'nameref'
  default aliases have been converted into regular built-in commands, so
  that 'unalias -a' does not remove them. Shell functions can now use
  these names, which improves compatibility with POSIX shell scripts.

- The End key escape sequence '^[[F' is now handled in the emacs and vi editing
  modes. The End key moves the cursor to the end of the line (in contrast to
  the Home key doing the opposite).

2020-07-14:

- Fixed a bug that caused 'set -b' to have no effect.

- Following the 'time' keyword, the 'times' builtin command now also
  supports millisecond precision.

2020-07-13:

- Fixed a fork bomb that could occur when the vi editor was sent SIGTSTP
  while running in a ksh script.

- Appending a lone percent to the end of a format specifier no longer
  causes a syntax error. The extra percent will be treated as a literal
  '%', like in Bash and zsh.

- The 'time' keyword now has proper support for millisecond precision.
  Although this feature was previously documented, the 'time' keyword
  only supported up to centisecond precision, which caused a command
  like the one below to return '0.000' on certain operating systems:
  $ TIMEFORMAT='%3R'; time sleep .003

- The 'time' keyword now zero-pads seconds less than ten (like mksh).

2020-07-10:

- Fixed a bug that caused types created with 'typeset -T' to throw an error
  when used if the type name started with a lowercase 'a'.

- A potential crash due to memory corruption when using many file
  descriptors has been fixed.

2020-07-09:

- Fixed a crash on syntax error when sourcing/dotting multiple files.

- Fixed a crash when listing indexed arrays.

- Fixed a memory leak when restoring PATH when temporarily setting PATH
  for a command (e.g. PATH=/foo/bar command ...) or in a virtual subshell.

- Combining ((...)) with redirections no longer causes a syntax error
  due to the parser handling '>' incorrectly.

- Fixed a bug that corrupted KIA/CQL cross-reference databases created using
  ksh's -R option; shell warnings were wrongly included in the database file.

- The shell's quoting algorithm (used in xtrace, printf %q, and more) has been
  fixed for UTF-8 (Unicode) locales; it no longer needlessly and inconsistently
  encodes normal printable UTF-8 characters into hexadecimal \u[xxxx] codes.

2020-07-07:

- Four of the date formats accepted by 'printf %()T' have had their
  functionality altered to the common behavior of date(1):
  - '%k' and '%l' print the current hour with blank padding, the former
    based on a 24-hour clock and the latter a 12-hour clock. These are
    common extensions present on Linux and *BSD.
  - '%f' prints a date with the format string '%Y.%m.%d-%H:%M:%S' (BusyBox).
  - '%q' prints the quarter of the year (GNU).

2020-07-06:

- 'notty' is now written to the ksh auditing file instead of '(null)' if
  the user's tty could not be determined.

- Unsetting an associative array no longer causes a memory leak to occur.

2020-07-05:

- In UTF-8 locales, fix corruption of the shell's internal string quoting
  algorithm (as used by xtrace, 'printf %q', and more) that occurred when
  the processing of a multibyte character was interrupted.

2020-07-03:

- Backslashes are no longer escaped in the raw Bourne Shell-like editing
  mode in multibyte locales, i.e. backslashes are no longer treated like
  Control-V if the emacs and vi modes are disabled.

- Deleting a backslash in vi mode with Control-H or Backspace now only
  escapes a backslash if it was the previous input. This means erasing a
  string such as 'ab\\\' will only cause the first backslash to escape a
  Backspace as '^?', like in emacs mode.

- An odd interaction with Backspace when the last character of a separate
  buffer created with Shift-C was '\' has been fixed. '^?' will no longer
  be output repeatedly when attempting to erase a separate buffer with
  a Backspace. Note that buffers created with Shift-C are not meant to be
  erasable:
  https://pubs.opengroup.org/onlinepubs/9699919799/utilities/vi.html#tag_20_152_13_49

- The 'kill' builtin now supports the SIGINFO signal (on operating systems
  with support for SIGINFO).

2020-07-02:

- Fixed a crash that occurred if a directory named '.paths' existed in any
  directory listed in $PATH. The fix was to only read '.paths' if it is a
  regular file or a symlink to a regular file.

2020-06-30:

- 'read -u' will no longer crash with a memory fault when given an out of
  range or negative file descriptor.

- The '=~' operator no longer raises an error if a regular expression
  combines the '{x}' quantifier with a sub-expression.

2020-06-28:

- Variables created with 'typeset -RF' no longer cause a memory fault
  when accessed.

- Unsetting an array that was turned into a compound variable will no
  longer cause silent memory corruption.

- Variables created with 'readonly' in functions are now set to the
  specified value instead of nothing. Note that 'readonly' does not
  create a function-local scope, unlike 'typeset -r' which does.

2020-06-26:

- Changing to a directory that has a name starting with a '.' will no
  longer fail if preceded by '../' (i.e. 'cd ../.local' will now work).

2020-06-24:

- Fixed buggy tab completion of tilde-expanded paths such as
  ~/some in 'vi' mode.

- In the raw/default Bourne Shell-like editing mode that occurs when neither
  the 'emacs' nor the 'vi' shell option is active:
  * tab completion is now correctly disabled, instead of enabled and broken;
  * entering tab characters now moves the cursor the correct amount.

2020-06-23:

- Fixed a bug that caused combining process substitution with redirection
  to create a bizarre file in the user's current working directory.

- Using process substitution while the shell is interactive no longer
  causes the process ID of the asynchronous process to be printed.

2020-06-22:

- The 'stop' and 'suspend' default aliases have been converted into regular
  built-in commands, so that 'unalias -a' does not remove them, 'suspend'
  can do a couple of sanity checks, and something like
	cmd=stop; $cmd $!
  will now work. See 'stop --man' and 'suspend --man' for more information.

- Fixed a bug that caused the kill and stop commands to segfault when given
  a non-existent job.

- Nested functions no longer ignore variable assignments that were prefixed
  to their parent function, i.e. 'VAR=foo func' will now set $VAR to 'foo'
  in the scope of any nested function 'func' runs.

2020-06-20:

- Fixed a bug that caused setting the following variables as readonly in
  a virtual subshell to affect the environment outside of the subshell:
  $_
  ${.sh.name}
  ${.sh.subscript}
  ${.sh.level}
  $RANDOM
  $LINENO

- Fixed two bugs that caused 'unset .sh.lineno' to always produce a memory
  fault and '(unset .sh.level)' to memory fault when run in nested
  functions.

2020-06-18:

- A two decade old bug that caused 'whence -a' to base the path of
  tracked aliases on the user's current working directory has been
  fixed. Now the real path to tracked aliases is shown when '-a' is
  passed to the whence command.

2020-06-17:

- A bug in 'unset -f' was fixed that prevented shell functions from
  unsetting themselves while they were running. A POSIX function no longer
  crashes when doing so, and a KornShell-style function no longer silently
  ignores an 'unset -f' on itself. A function of either form now continues
  running after unsetting itself, and is removed at the end of the run.

2020-06-16:

- Passing the '-d' flag to the read builtin will no longer cause the '-r'
  flag to be discarded when 'read -r -d' is run.

- Fix BUG_CMDSPASGN: preceding a "special builtin"[*] with 'command' now
  prevents preceding invocation-local variable assignments from becoming global.
  [*] https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_14

2020-06-15:

- The 'source' alias has been converted into a regular built-in command.

- Functions that set variables in a virtual subshell will no longer affect
  variables of the same name outside of the virtual subshell's environment.

- Terse usage messages written by builtin commands now point the user to
  the --help and --man options for more information.

2020-06-14:

- 'read -S' is now able to correctly handle strings with double quotes
  nested inside of double quotes.

2020-06-13:

- Fixed a timezone name determination bug on FreeBSD that caused the
  output from "LC_ALL=C printf '%T\n' now" to print the wrong time zone name.

2020-06-11:

- Fixed a bug that caused running 'builtin -d' on a special builtin to
  delete it. The man page for the 'builtin' command documents that special
  builtins cannot be deleted.

- POSIX compliance fix: It is now possible to set shell functions named
  'alias' or 'unalias', overriding the commands by the same names. In
  technical terms, they are now regular builtins, not special builtins.

- The redirect='command exec' alias has been converted to a regular
  'redirect' builtin command that only accepts I/O redirections, which
  persist as in 'exec'. This means that:
  * 'unlias -a' no longer removes the 'redirect' command;
  * users no longer accidentally get logged out of their shells if
    they type something intuitive but wrong, like 'redirect ls >file'.

- The undocumented 'login' and 'newgrp' builtin commands have been removed.
  These replaced your shell session with the external commands by the same
  name, as in 'exec'. If an error occurred (e.g. due to a typo), you would
  end up immediately logged out.
  If you do want this behaviour, you can restore it by setting:
	alias login='exec login'
	alias newgrp='exec newgrp'

2020-06-10:

- The 'hash' utility is now a regular builtin instead of an alias to
  'alias -t --'. The functionality of the old command has been removed
  from the alias builtin.

- 'set +r' is no longer able to unset the restricted option. This change
  makes the behavior of 'set +r' identical to 'set +o restricted'.

2020-06-09:

- The 'unalias' builtin will now return a non-zero status if it tries
  to remove a previously set alias that is not currently set.

2020-06-08:

- Fix an issue with the up arrow key in Emacs editing mode.
  Emacs editing mode is bugged in ksh93u+ and ksh2020. Let's
  say you were to run the following commands after starting
  a fresh instance of ksh:
  $ alias foo=true
  $ unalias foo
  If you type 'a' and then press the up arrow on your keyboard,
  ksh will complete 'a' to 'alias foo=true' by doing a reverse
  search for the last command that starts with 'a'.
  Run the alias command again, then type 'u' and press the up
  arrow key again. If ksh is in Vi mode, you will get 'unalias foo',
  but in Emacs mode you will get 'alias foo=true' again.
  All subsequent commands were ignored as ksh was saving the first
  command and only based later searches off of it.

- If 'set -u'/'set -o nounset' is active, then the shell now errors out if a
  nonexistent positional parameter such as $1, $2, ... is accessed, as other
  shells do and POSIX requires. (This does *not* apply to "$@" and "$*".)

- If 'set -u'/'set -o nounset' is active, then the shell now errors out if $!
  is accessed before the shell has launched any background process.

- Removed support for an obscure early 1990s Bell Labs file system research
  project called 3DFS, which has not existed for decades. This removes:
  - an obnoxious default alias 2d='set -f;_2d' that turned off your file name
    wildcard expansion and then tried to run a nonexistent '_2d' command
  - undocumented builtins 'vmap' and 'vpath' that only printed error messages
  - a non-functional -V unary operator for the test and [[ commands

- If the last program run by a ksh script exits with a signal (e.g. crashed),
  ksh itself now exits normally instead of repeating that same signal.
  In addition, using 'exit x' for x > 256 no longer makes ksh issue a signal.

2020-06-06:

- The 'times' command is now a builtin command that conforms to POSIX
  instead of an alias for the 'time' command. It displays the accumulated
  user and system CPU times, one line with the times used by the shell and
  another with those used by all of the shell's child processes.
  https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_27

- The default aliases command='command ' and nohup='nohup ' have been
  removed because they caused breakage in an attempt to circumvent other
  breakage which is being fixed. In the unlikely even that anyone still
  needs alias substitution to continue on the command argument following
  'command' or 'nohup', it's easy to set these aliases yourself.

2020-06-05:

- Fix a bug that caused special variables such as PATH, LANG, LC_ALL,
  etc. to lose their effect after being unset in a subshell. For example:
    (unset PATH; PATH=/dev/null; ls); : wrongly ran 'ls'
    (unset LC_ALL; LC_ALL=badlocale); : failed to print a diagnostic
  This also fixes BUG_KUNSETIFS: unsetting IFS in a subshell failed if IFS
  was set to the empty value in the parent shell.

- Fix crashes on some systems, including at least a crash in 'print -v' on
  macOS, by eliminating an invalid/undefined use of memccpy() on overlapping
  buffers in the commonly used sfputr() function.

- Fix the ${.sh.subshell} level counter; it is no longer reset to zero when a
  non-forked subshell happens to fork into a separate process for some reason
  (an internal implementation detail that should be unnoticeable to scripts).

2020-06-04:

- Fix BUG_KBGPID: the $! special parameter was not set if a background job
  (somecommand &) or co-process (somecommand |&) was launched as the only
  command within a braces block with an attached redirection, for example:
	{
		somecommand &
	} >&2
  With the bug, $! was unchanged; now it contains the PID of somecommand.

2020-05-31:

- Fix a bug in autoloading functions. Directories in the path search list
  which should be skipped (e.g. because they don't exist) did not interact
  correctly with autoloaded functions, so that a function to autoload was
  not always found correctly.
  Details: https://github.com/att/ast/issues/1454

2020-05-30:

- Fix POSIX compliance of 'test'/'[' exit status on error. The command now
  returns status 2 instead of 1 when given an invalid number or arithmetic
  expression, e.g.:
	[ 123 -eq 123x ]; echo $?
  now outputs 2 instead of 1.

2020-05-29:

- Fix BUG_FNSUBSH: functions can now be correctly redefined and unset in
  subshell environments (such as ( ... ), $(command substitutions), etc).
  Before this fix, this was silently ignored, causing the function by the
  same name from the parent shell environment to be executed instead.
	fn() { echo mainsh; }
	(fn() { echo subsh; }; fn); fn
  This now correctly outputs "subsh mainsh" instead of "mainsh mainsh".
	ls() { echo "ls executed"; }
	(unset -f ls; ls); ls
  This now correctly lists your directory and then prints "ls executed",
  instead of printing "ls executed" twice.

- Fix a similar bug with aliases. These can now be correctly unset
  in subshell environments.

2020-05-21:

- Fix truncating of files with the combined redirections '<>;file' and
  '<#pattern'. The bug was caused by out-of-sync streams.
  Details and discussion: https://github.com/att/ast/issues/61

- Patched code injection vulnerability CVE-2019-14868. As a result, you can
  no longer use expressions in imported numeric environment variables; only
  integer literals are allowed.

2020-05-20:

- Fix BUG_ISSETLOOP. Expansions like ${var+set} remained static when used
  within a 'for', 'while' or 'until' loop; the expansions din't change along
  with the state of the variable, so they could not be used to check whether a
  variable is set within a loop if the state of that variable changed in the
  course of the loop.

- Fix BUG_IFSISSET. ${IFS+s} always yielded 's', and [[ -v IFS ]] always
  yielded true, even if IFS is unset. This applied to IFS only.

2020-05-19:

- Fix 'command -p'. The -p option causes the operating system's standard
  utilities path (as output by 'getconf PATH') to be searched instead of $PATH.
  Before this fix, this was broken on non-interactive shells as the internal
  variable holding the default PATH value was not correctly initialised.

2020-05-16:

- Fix 'test -t 1', '[ -t 1 ]', '[[ -t 1 ]]' in command substitutions.
  Standard output (file descriptor 1) tested as being on a terminal within a
  command substitution, which makes no sense as the command substitution is
  supposed to be catching standard output.
	v=$(echo begincomsub
	    [ -t 1 ] && echo oops
	    echo endcomsub)
	echo "$v"
  This now does not output "oops".

2020-05-14:

- Fix syncing history when print -s -f is used. For example, the
  following now correctly adds a 'cd' command to the history:
	print -s -f 'cd -- %q\n' "$PWD"
  Ref.:	https://github.com/att/ast/issues/425
	https://github.com/att/ast/pull/442

- Fix BUG_PUTIOERR: Output builtins now correctly detect
  input/output errors. This allows scripts to check for a nonzero exit
  status on the 'print', 'printf' and 'echo' builtins and prevent possible
  infinite loops if SIGPIPE is ignored.

- Add a convenient bin/shtests script to the source tree that sets up the
  necessary environment and runs the ksh regression tests.

2020-05-13:

- Fix BUG_CASELIT: an undocumented 'case' pattern matching misbehaviour that
  goes back to the original Bourne shell, but wasn't discovered until 2018.
  If a pattern doesn't match as a pattern, it was tried again as a literal
  string. This broke common validation use cases, e.g.:
      n='[0-9]'
      case $n in
      ( [0-9] )  echo "$n is a number" ;;
      esac
  would output "[0-9] is a number" as the literal string fallback matches the
  pattern. As this misbehaviour was never documented anywhere (not for Bourne,
  ksh88, or ksh93), and it was never replicated in other shells (not even in
  ksh88 clones pdksh and mksh), it is unlikely any scripts rely on it.
     Of course, a literal string fallback, should it be needed, is trivial to
  implement correctly without this breakage:
      case $n in
      ( [0-9] | "[0-9]")  echo "$n is a number or the number pattern" ;;
      esac
  Ref.: https://github.com/att/ast/issues/476

- Fix BUG_REDIRIO: ksh used to redirect standard output by default when no
  file descriptor was specified with the rarely used '<>' reading/writing
  redirection operator. It now redirects standard input by default, as POSIX
  specifies and as all other POSIX shells do. To redirect standard output
  for reading and writing, you now need '1<>'.
  Ref.:	https://github.com/att/ast/issues/75
	https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_07_07

2020-05-12:

- ksh development rebooted based on 93u+ 2012-08-01.