Shell Programming and Scripting

I have a number of Korn scripts I've used successfully for years in AIX (4.3 and 5.x) and Solaris (9 and 10). Recently I've had to start porting them to HP-UX (11i V3) and run into a few unexpected incompatabilities. For one, the "!" operator does not seem to work reliably (as in "if (! command) ..."), nor does the "==" operator.

I've researched this a bit, and from what I've seen it appears that HP's version of ksh is rather old (11/16/88c). Does anyone know of a list of differences between HP's ksh and more modern ones, perhaps with ideas on how to program around them? In a few cases, it's gotten messy enought that I simply gave up and changed the calling shell to bash, which works reasonably well, but there are enough differences there that that's not a one-size-fits-all solution, either.

Thanks,
Steve

You have illustrated the reasons for using only POSIX syntax in scripts.

The man pages for ksh88 and ksh93 are at: KornShell Documentation.

The POSIX shell on HP-UX is /usr/bin/sh .
See "man sh" for an explanation of the various shells.
BTW. The syntax you describe looks more like "csh" than "ksh". An "if" test in "ksh" would have square brackets not round brackets. Also the "==" is valid in "csh".

man sh-posix for information on the POSIX shell.

While I agree, I'm not sure I see your point. O'Reilly's "Learning the Korn Shell" makes no mention of POSIX concerns with either of my examples. (In fact, page 143 of the 2nd edition specifically states that the "!" keyword was introduced in POSIX.) I'm certainly no POSIX guru, though, so perhaps I've misunderstood your intent.

In any case, if HP's ksh is as old as it appears, it's probably not POSIX-compliant to start with, and using POSIX syntax may be the cause of the problem, not the solution. So my original question stands - does there exist a list of version incompatabilities between HP's ksh and more modern ones?

Believe it or not, I browse those pages often when I'm developing new scripts, and they recently went offline (again).

The script I'm currently working on contains the following:

Code:

# Check for debug mode switch
if [[ $1 == "-d" ]]
then
        # Set up debug mode
        debug=true
        shift
fi

On HP-UX 11i V3, both /bin/ksh and /usr/bin/sh choke with a syntax error (`==' unexpected). The original script runs fine on Solaris and AIX. What about this statement is non-POSIX? If I drop the test to single braces and change the "==" to "-eq" both ksh and sh are happy.

You're lucky, then. The -eq operator is for comparing integers, not strings.

The correct test (in any Bourne-type shell) is:

Code:

if [ "$1" = "-d" ]

But for parsing options, you should use getopts.

Correction noted. My point was that the "==" works on the other platforms I use and had no reason to think it would not work here. Is the "==" operator non-POSIX?