topic Re: if ! not working in ksh in Operating System - Linux

if ! not working in ksh

dictum9 — Tue, 13 Mar 2007 16:51:11 GMT

This is 11.0, N class machine.

I can get the following to work on the command line if I type it in, but not in a script. In a script, it complains about the "!".
The script starts with #!/bin/ksh.
Why is that, is there a bug?

if ! grep "Synchronizing" $STATE
then
echo not
else
echo yes
fi

Re: if ! not working in ksh

Tim Nelson — Tue, 13 Mar 2007 17:01:00 GMT

most likely need some quoting...

other option

if grep "Syncronizing" $STATE
then
echo yes
else
echo no
fi

Re: if ! not working in ksh

Tim Nelson — Tue, 13 Mar 2007 17:12:13 GMT

Now that I think more..

I do not think you can use "if !"

typically you would either "if true" or "if false". Not "if not true."

Re: if ! not working in ksh

James R. Ferguson — Tue, 13 Mar 2007 17:24:15 GMT

Hi:

This should be:

if [ `grep -c "Synchronizing" $STATE` -eq 0 ]
...

That is, it appears that you want to test whether or not there are any occurances of "Synchronizing" in the (file) ${STATE}.

Another way is to examine the return value of grep (zero meaning that there *is* a match):

# grep "Synchronizing" ${STATE} && echo "yes" || echo "no"

Regards!

...JRF...

Re: if ! not working in ksh

James R. Ferguson — Tue, 13 Mar 2007 19:19:52 GMT

Hi (again):

Ooops. The last suggestion is best done with the '-q'uiet switch (since you don't want the output; only the success or failure of the match:

# grep -q Synchronizing ${STATE} && echo yes || echo no

Regards!

...JRF...

Re: if ! not working in ksh

Dennis Handly — Wed, 14 Mar 2007 03:32:11 GMT

>Tim: I do not think you can use "if !"

Right, it is only available in [ ] or conditional expressions in [[ ]].
Or !(pattern-list).
And of course in arithmetic expressions in (( )) or let.

Re: if ! not working in ksh

Peter Nikitka — Wed, 14 Mar 2007 06:31:19 GMT

Hi,

this feature is not available in the standard ksh; in the ksh93 version, it is.
So if you want to try, use
/usr/dt/bin/dtksh
as the shell for your script.

mfG Peter

Re: if ! not working in ksh

dictum9 — Wed, 14 Mar 2007 08:41:35 GMT

I ended up not using "!" and reversing the if statement.

Still not real clear as to why it works in shell but not in the script.

Re: if ! not working in ksh

OldSchool — Wed, 14 Mar 2007 11:18:31 GMT

"Still not real clear as to why it works in shell but not in the script...."

well, it would appear that the shell you work in is not ksh.

easy test, type in /bin/ksh and then enter the command. does it work?

Re: if ! not working in ksh

Daavid Turnbull — Wed, 14 Mar 2007 23:43:08 GMT

It is shell specific so it may depend on what you have as your #! line at the top which I suspect points at a different shell.

"man test" is your friend for this sort of stuff.

I tend to be a bit old school and tend to do something like:

grep -q "some string" "some file"
if [ $? -ne 0 ]
then
echo "some string not found"
fi

Because to me it makes it clear that it is the exit code that is being Analyzed in the conditional.

Re: if ! not working in ksh (need sh or dtksh)

Dennis Handly — Mon, 10 Oct 2011 03:54:47 GMT

>Peter: this feature is not available in the standard ksh

You're right, it is highlighted on my sh-posix(1) entry. ;-)

>OldSchool: it would appear that the shell you work in is not ksh.

Most likely, sh.

>Still not real clear ... but not in the script.

Change to: #!/bin/sh.

>Daavid: "man test" is your friend for this sort of stuff.

Not if you are using ksh or the posix shell. And test(1) is only for stuff in [...].

And more importantly, test(1) just invokes the posix shell.

Re: if ! not working in ksh

James R. Ferguson — Thu, 15 Mar 2007 07:16:48 GMT

Hi (again):

> Dennis wrote :Change to: #!/bin/sh.

To be clear, '/bin' is a link to '/usr/bin'. '/usr/bin/sh' is the POSIX shell in HP-UX. The Korn-88 shell is represented by '/usr/bin/ksh' and the Korn-93 shell can be found as '/usr/dt/bin/dtksh'. The (useless?) Bourne shell can be found as '/usr/old/bin/sh'.

Regards!

...JRF...