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ksh-20120801
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COMPATIBILITY
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KSH-93 VS. KSH-88 The following is a list of known incompatibilities between ksh-93 and ksh-88. I have not include 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, maintain compatibility. This 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 where 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 parenthes within ${name op val} whereas ksh-93 does not. Thus, ${foo-(} needs to be written as ${foo-\(} which works with both versions. 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 recongnized, 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 exeucted 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.