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, ksh93 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

ksh93. In ksh88 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 ksh88. Most of these

differences were eliminated in ksh93o.

24. Starting after ksh93l, 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 ksh93, cd - will output the directory that it changes

to on standard output as required by X/Open. With ksh88,

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 ksh93p.

27. The getopts builtin in ksh93 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.

I am interested in expanding this list so please let me know if you

uncover any others.