[Gllug] Bourne shell programming

[Mike Brodbelt]

Tethys wrote:

>> Now variables I set inside the loop vanish, as the pipe causes a
>> subshell to be spawned, so I can't set variables in the body of my
>> loop that are visible to the rest of the script.
> 
> Yep. It's the single most annoying feature of shell scripting[1].

Yes, after spending far too long fighting to achieve a simple result, I
think I'd go with that view :-)

> If you're using bash or zsh, you can get around it by using process
> substitution:
> 
> 	while read x
> 	do
> 		some stuff
> 	done < <(grep root /etc/passwd | awk -F: '{print $1,$2,$3}')

Clever, but ewwwww :-).

> If you're using a traditional Bourne or Korn[2] shell

Yep - it's in a shell script on a Solaris box, so it's a hoary old
Bourne shell.

<snip>

> It's crude and ugly, but it works. You can, of course, use multiple
> temporary files if you have multiple values to return (which is even
> more ugly, but easier than trying to multiplex multiple values into
> a single file).

I ended up last night using temp files, but I've found a route today
which I'm happier with for this particular script, which was to do it like:-

output=`grep root /etc/passwd | awk -F: '{print $1,$2,$3}'`
for line in $output
do
	stuff
done

which just provides a different route to get information back from the
subshell. Thanks for the help - much appreciated. I don't do a lot of
shell, and it always seems painful :-)

Mike
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