dgk@ulysses.UUCP (David Korn) (06/12/84)
KSH VS. SH I have not made a complete comparison between S5R2 /bin/sh and ksh. A direct comparison of the manuals may uncover more incompatibilities than I have listed here. In addition, I have omitted some incompatibilities that are bugs in S5R2 sh that may have been fixed for S5R2. I have also omitted incompatibilities in cases that sh clearly is incorrect, such as in cases where it core dumps. I have also omitted cases which are bugs in ksh. I have also omitted built-ins since this can be circumvented by using the alias facility if necessary. The following is a list of known incompatibilities between ksh and sh: 1. The IFS parameter is only effective for set, for and read in ksh. Thus, IFS=x;exit will execute e on the file it with sh but will exit with ksh. 2. If an environment parameter is modified by ksh, the new value will be passed to the children. In sh you must export the parameter for this to happen. 3. Time is a reserved word in ksh. Thus time a | b will time the pipeline in ksh while only a will be timed with sh. You can also time built-in commands and functions with ksh, you can't with sh. 4. Select and function are reserved words in ksh. 5. Parameter assignments only have scope for the command or function they precede in ksh. In sh, built-in commands and functions treat parameter assignments as globals. (Notice that S5R2 and S5R1 treat parameter assignments to pwd and echo in an incompatible way). 6. The output of some built-in commands and error messages is different in a few cases, for example times produces two lines of output in ksh. 7. While loops with redirection are not executed in a separate process in ksh so assignments made within loops remain in effect after the loop completes. 8. The semantics of functions are somewhat different. Ksh can have local variables and allow recursive functions. Errors in functions abort the function but not the script that they are in. 9. The name space for functions and variables is separate in ksh. In /bin/sh they share the same space. The unset builtin requires a -f flag to unset a function in ksh. 10. Words that begin with ~ may be expanded in ksh. Sh does not have this feature. 11. The character ^ is not special in ksh. In sh it is an archaic synonym for |. 12. Whenever (( occurs where a command name is valid, ksh assumes that an arithmetic expression follows. In sh this means a sub-shell inside a sub-shell. 13. Non-blank contiguous IFS delimiters generate a null input argument. Therefore, you can use IFS=: and correctly read the /etc/profile file even when fields are omitted. In sh, multiple delimiters count as a single delimiter. 14. Arithmetic test comparison operators (-eq, -lt, ...) allow any arithmetic expressions. Sh allows only constants. If you say test x -eq 0 in sh, which is meaningless, it returns true, but in ksh it depends on the value of the variable x. If there is no variable x, then ksh produces an error message. 15. The environment handed down to a program is not sorted in ksh. A user should not reply in this quirk of sh since any user program can provide an environment list which does not have to be sorted. (Getenv(3) does not assume a sorted list). 16. There is an alias hash in ksh which does what the S5R2 has built-in does except for the -r flag. In ksh, you must say PATH=$PATH to achieve the same result. 17. The expansion of "$@" with no arguments produces the null string in the Bourne shell and produces nothing with ksh when there are no arguments. I am not sure whether this is a bug in the Bourne shell or intentional. The manual page leads me to think that it is a bug. I am interested in expanding this list so please let me know if you uncover any others. David Korn ulysses!dgk