Really strange problem

leeharris · 02-12-2009, 12:33 PM

Hi,

I have a really strange problem that's giving me some major headaches and wondered if the bright minds of linuxquestions might be able to help me out.

This problem is two fold really... I shall explain...

I've got a script in which I need to pass variables from within a loop back to the main script. Using pipes in a loop in bash apparently spawns a subshell and as such the variable values are lost once the loop exits.

So, I had something like this...

Code:

cat file.txt | while read line
do
something
retval=$?
done

echo ${retval}

This didn't work because of the pipe / subshell thing...so I changed it to this...

Code:

while read line
do
something
retval=$?
done < <(cat file.txt)

echo ${retval}

Now this worked fine while I was testing it using the default bash shell on a RedHat EL 4 box.

However, the script is to be used in an automation product (BladeLogic), and when that executes the script it uses /bin/sh to do it instead of /bin/bash and it fails with a message like unexpected < near token ( or some such, basically a syntax error.

Now the really weird thing is, that when I tested the script manually again, still on the same server, I found that if executed it like this...

Code:

/bin/bash myscript

...it worked. But if I did this...

Code:

/bin/sh myscript

...it failed with the syntax error.

But now the really strange part. If on the same server I do which sh it tells me /bin/sh, and if I do ls -l /bin/sh it shows me it that /bin/sh is just a symbolic link to /bin/bash!

And I am completely stumped by this :-(

Thanks - Lee

gnashley · 02-12-2009, 01:01 PM

When called as 'sh', bash behaves differently than if called as 'bash' -it runs more POSIX-ly conformant with only a few extensions. This works for me:

Code:

#/bin/sh
while read line
do
something
retval=$?
done < file.txt

echo ${retval}

leeharris · 02-12-2009, 01:35 PM

Hi, yeah I tried the single < but I need to evaluate a command, and doing < (command) didnt work either. But I think I've cracked it... sort of.

As mush as I don't really like this solution, it will have to do for now and that is to stick

Code:

set +o posix

at the top of the script. That seems to work fine now!

Thanks!

chrism01 · 02-12-2009, 06:05 PM

Maybe if you showed us what you're really doing we could come up with a better soln?

gnashley · 02-13-2009, 06:35 AM

You might also try this:
< $(command)
and especially this:
< `command`