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Editing: COMPATIBILITY
ksh 93u+m/1.0.5 vs. ksh 93u+ The following is a list of changes between ksh 93u+ 2012-08-01 and the new ksh 93u+m reboot that could cause incompatibilities in rare corner cases. Fixes of clear bugs in ksh 93u+ are not included here, even though any bugfix could potentially cause an incompatibility in a script that relies on the bug. For more details, see the NEWS file and for complete details, see the git log. 0. A new '-o posix' shell option has been added to ksh 93u+m that makes the ksh language more compatible with other shells by following the POSIX standard more closely. See the manual page for details. It is enabled by default if ksh is invoked as sh. 1. Bytecode compiled by shcomp 93u+m will not run on older ksh versions. (However, bytecode compiled by older shcomp will run on ksh 93u+m.) 2. Pathname expansion (a.k.a. filename generation, 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 'dotfiles' in the current directory. 3. The bash-style &>foo redirection operator (shorthand for >foo 2>&1) can now always be used if -o posix is off, and not only in profile scripts. 4. Redirections that store a file descriptor > 9 in a variable, such as {var}>file, now continue to work if brace expansion is turned off. 5. Most predefined aliases have been converted to regular built-in commands that work the same way. 'unalias' no longer removes these. To remove a built-in command, use 'builtin -d'. The 'history' and 'r' predefined aliases remain, but are now only set on interactive shells. There are some minor changes in behavior in some former aliases: - 'redirect' now checks if all arguments are valid redirections before performing them. If an error occurs, it issues an error message instead of terminating the shell. - 'suspend' now refuses to suspend a login shell, as there is probably no parent shell to return to and the login session would freeze. If you really want to suspend a login shell, use 'kill -s STOP $$'. - 'times' now gives high precision output in a POSIX compliant format. 6. 'command' and 'nohup' no longer expand aliases in their first argument, as this is no longer required after the foregoing change. In the unlikely event that you still need this behavior, you can set: alias command='command ' alias nohup='nohup ' 7. The 'login' and 'newgrp' special built-in commands have been removed, so it is no longer an error to define shell functions by these names. These built-ins 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, except on a few commercial Unix systems whose 'login' and 'newgrp' cope with this by starting a new shell session upon error. If you do want the old behavior, you can restore it by setting: alias login='exec login' alias newgrp='exec newgrp' 8. 'case' no longer retries to match patterns as literal strings if they fail to match as patterns. This undocumented behaviour broke validation use cases that are expected to work. For example: n='[0-9]' case $n in [0-9]) echo "$n is a digit" ;; esac would output "[0-9] is a digit". In the unlikely event that a script does rely on this behavior, it can be fixed like this: case $n in [0-9] | "[0-9]") echo "$n is a digit or the digit pattern" ;; esac 9. If 'set -u'/'set -o nounset' is active, then the shell now errors out if a nonexistent positional parameter such as $1, $2, ... is accessed. (This does *not* apply to "$@" and "$*".) 10. 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. 11. The 'print', 'printf' and 'echo' built-in commands now return a nonzero exit status if an input/output error occurs. 12. Four obsolete date format specifiers for 'printf %(format)T' were changed to make them compatible with modern date(1) commands: - %k and %l now return a blank-padded hour (24-hour and 12-hour clock). - %f now returns a date with the format '%Y.%m.%d-%H:%M:%S'. - %q now returns the quarter of the current year. 13. The 'typeset' built-in now properly detects and reports options that cannot be used together if they are given as part of the same command. 14. The DEBUG trap has reverted to pre-93t behavior. It is now once again reset like other traps upon entering a subshell or ksh-style function, as documented, and it is no longer prone to crash or get corrupted. A new --functrace shell option has been added that, when turned on, makes subshells and functions correctly inherit the DEBUG trap. 15. 'command -x' now always runs an external command, bypassing built-ins. 16. Unbalanced quotes and backticks now correctly produce a syntax error in -c scripts, 'eval', and backtick-style command substitutions. 17. -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 expected. 18. The variable name search expansions ${!prefix@} and ${!prefix*} now also include the variable 'prefix' itself in the possible results. 19. [[ -v var ]] is now properly equivalent to [[ -n ${var+set} ]]. Undocumented special-casing for numeric types has been removed. For example, the following no longer produces an unexpected error: $ ksh -o nounset -c 'float n; [[ -v n ]] && echo $n' 20. If the HOME variable is unset, the bare tilde ~ now expands to the current user's system home directory instead of merely the username. 21. On Windows/Cygwin, globbing is no longer case-insensitive by default. Turning on the new --globcasedetect shell option restores case-insensitive globbing for case-insensitive file systems. 22. If $PWD or $OLDPWD are passed as invocation-local assignments to cd, their values are no longer altered in the outer scope when cd finishes. For example: ksh -c 'OLDPWD=/bin; OLDPWD=/tmp cd - > /dev/null; echo $OLDPWD' ksh -c 'cd /var; PWD=/tmp cd /usr; echo $PWD' now prints '/bin' followed by '/var'. 23. 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: $ /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 In the event an external command by that path exists, the path-bound built-in will now override it when invoked using the canonical path. To invoke a possible external command at that path, you can still use a non-canonical path, e.g.: /opt//ast/bin/cat or /opt/ast/./bin/cat 24. The readonly attribute of ksh variables is no longer imported from or exported to other ksh shell instances through the environment. 25. 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, $RANDOM is now reseeded (as mksh and bash do). 26. The built-in arithmetic function int() has changed to round towards zero instead of negative infinity. Previously, int() was an alias to floor(), but now it behaves like trunc(). 27. The '!' logical negation operator in the '[[' compound command now correctly negates another '!', e.g., [[ ! ! 1 -eq 1 ]] now returns 0/true. Note that this has always been the case for 'test'/'['. 28. By default, arithmetic expressions in ksh no longer interpret a number with a leading zero as octal in any context. Use 8#octalnumber instead. Before, ksh would arbitrarily recognize the leading octal zero in some contexts but not others. One of several examples is: x=010; echo "$((x)), $(($x))" would output '10, 8'. This now outputs '10, 10'. 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. 29. It is now an error for arithmetic expressions to assign an out-of-range index value to a variable of an enumeration type created with 'enum'. 30. 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. 31. The 'enum' and 'typeset -T' commands are no longer allowed to override and replace special built-in commands, except for type definition commands previously created by these commands. 32. The .sh.level variable is now read-only except inside a DEBUG trap. The current level/scope is now restored when the DEBUG trap run ends. 33. 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/*. 34. Single and double quotes now work like backslashes to quote '!', '^' and '-' in bracket expressions in shell glob patterns, e.g., the glob pattern ["!a-z"] now matches !, a, - or z and is no longer misparsed as [!a-z]. This restores compatibility with ksh88 and non-ksh shells. 35. 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 ${parameter}). ____________________________________________________________________________ KSH-93 VS. KSH-88 (Written by David Korn for ksh 93u+ 2012-08-01) The following is a list of known incompatibilities between ksh-93 and ksh-88. I have not included cases that are clearly bugs in ksh-88. I also have omitted features that are completely upward compatible. 1. Functions, defined with name() with ksh-93 are compatible with the POSIX standard, not with ksh-88. No local variables are permitted, and there is no separate scope. Functions defined with the function name syntax have local variables as in ksh-88, but are statically scoped as in C so that a function does not automatically have access to local variables of the caller. This change also affects function traces. 2. ! is now a reserved word. As a result, any command by that name will no longer work with ksh-93. 3. The -x attribute of alias and typeset -f is no longer effective and the ENV file is only read for interactive shells. You need to use FPATH to make function definitions visible to scripts. 4. A built-in command named command has been added which is always found before the PATH search. Any script which uses this name as the name of a command (or function) will not be compatible. 5. The output format for some built-ins has changed. In particular the output format for set, typeset and alias now have single quotes around values that have special characters. The output for trap without arguments has a format that can be used as input. 6. With ksh-88, a dollar sign ($') followed by a single quote was interpreted literally. Now it is an ANSI C string. You must quote the dollar sign to get the previous behavior. Also, a $ in front of a " indicates that the string needs to be translated for locales other than C or POSIX. The $ is ignored in the C and POSIX locale. 7. With ksh-88, tilde expansion did not take place inside ${...}. with ksh-93, ${foo-~} will cause tilde expansion if foo is not set. You need to escape the ~ for the previous behavior. 8. Some changes in the tokenizing rules were made that might cause some scripts with previously ambiguous use of quoting to produce syntax errors. 9. Programs that rely on specific exit values for the shell, (rather than 0 or non-zero) may not be compatible. The exit status for many shell failures has been changed. 10. Built-ins in ksh-88 were always executed before looking for the command in the PATH variable. This is no longer true. Thus, with ksh-93, if you have the current directory first in your PATH, and you have a program named test in your directory, it will be executed when you type test; the built-in version will be run at the point /bin is found in your PATH. 11. Some undocumented combinations of argument passing to ksh builtins no longer works since ksh-93 is getopts conforming with respect to its built-ins. For example, typeset -8i previously would work as a synonym for typeset -i8. 12. Command substitution and arithmetic expansion are now performed on PS1, PS3, and ENV when they are expanded. Thus, ` and $( as part of the value of these variables must be preceded by a \ to preserve their previous behavior. 13. The ERRNO variable has been dropped. 14. If the file name following a redirection symbol contain pattern characters they will only be expanded for interactive shells. 15. The arguments to a dot script will be restored when it completes. 16. The list of tracked aliases is not displayed with alias unless the -t option is specified. 17. The POSIX standard requires that test "$arg" have exit status of 0, if and only if $arg is null. However, since this breaks programs that use test -t, ksh-93 treats an explicit test -t as if the user had entered test -t 1. 18. The ^T directive of emacs mode has been changed to work the way it does in gnu-emacs. 19. ksh-88 allowed unbalanced parentheses within ${name op val} whereas ksh-93 does not. Thus, ${foo-(} needs to be written as ${foo-\(} which works with both versions. [2021 UPDATE: This is now once again allowed in ksh 93u+m. Note that balanced parentheses ${foo-()} were also broken and are now fixed.] 20. kill -l in ksh-93 lists only the signal names, not their numerical values. 21. Local variables defined by typeset are statically scoped in ksh-93. In ksh-88 they were dynamically scoped although this behavior was never documented. 22. The value of the variable given to getopts is set to ? when the end-of-options is reached to conform to the POSIX standard. 23. Since the POSIX standard requires that octal constants be recognized, doing arithmetic on typeset -Z variables can yield different results that with ksh-88. Most of these differences were eliminated in ksh-93o. Starting in ksh-93u+, the let command no longer recognizes octal constants starting with 0 for compatibility with ksh-88 unless the option letoctal is on. 24. Starting after ksh-93l, If you run ksh name, where name does not contain a /, the current directory will be searched before doing a path search on name as required by the POSIX shell standard. 25. In ksh-93, cd - will output the directory that it changes to on standard output as required by X/Open. With ksh-88, this only happened for interactive shells. 26. As an undocumented feature of ksh-88, a leading 0 to an assignment of an integer variable caused that variable to be treated as unsigned. This behavior was removed starting in ksh-93p. 27. The getopts builtin in ksh-93 requires that optstring contain a leading + to allow options to begin with a +. 28. In emacs/gmacs mode, control-v will not display the version when the stty lnext character is set to control-v or is unset. The sequence escape control-v will display the shell version. 29. In ksh-88, DEBUG traps were executed after each command. In ksh-93 DEBUG traps are executed before each command. 30. In ksh-88, a redirection to a file name given by an empty string was ignored. In ksh-93, this is an error. I am interested in expanding this list so please let me know if you uncover any others.
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