[Techtalk] re: Joining commands together in bash

[Random832]

On Mon, May 12, 2003 at 03:25:23AM -0700, Berenice wrote:
> This is great.  So now I've learned 2 new things about bash.
> 
> On Sun, May 11, 2003 at 12:34:07PM +0100, Meredydd wrote:
> > This is how I would do it:
> > 
> > for FILE in * ; do
> >   if [ x`file $FILE | grep 'shell script text executable'` != x ]; 
> > then
> >    head -n 3 $FILE
> >   fi
> > done
> 
> 
> Do newer versions of bash accept statements in the form of
> x`blahblah` != x  ?  I know you've said it works in older shells, but
> it doesn't seem to work in mine. I don't know if I'm typing it wrong,
> but I also tried `echo hi` at the command prompt and got the message
> "bash: hi: command not found".  Just wondering...
 
first, that's the expected result for `echo hi` at the command prompt:

"`echo hi`" evaluates to "hi"

if you typed just "hi" at the command prompt, you would also get command
not found.

`this` itself is a holdover from older shells, if you're using bash you
should use $(this) instead, since it works better for nesting.

the actual problem with the example was probably the `` statement
evaluated to multiple tokens... replace it with "``" or "$()"

the [ x.... != x ] construct has never made much sense to me, when
simply [ -n ...] works fine

given that, the example should be

for FILE in * ; do
  if [ -n "$(file $FILE | grep 'shell script text executable')" ];
then
   head -n 3 $FILE
  fi
done

however, it's much simpler to just check the return status of grep:

for FILE in *; do
  if file $FILE | (grep 'shell script text executable' >&/dev/null);
 then
   echo "-- $FILE --"
   head -n 3 $FILE
  fi
done

(i also added something you'll probably need, a separator line that
identifies the file)

that said, the xargs solution is probably a better way to do it.

> Date: Sun, 11 May 2003 21:46:52 +1000
> From: Malcolm Tredinnick <malcolm at commsecure.com.au>
> 
> >Straight out of the "more than one way to skin a cat" bucket, here
> is 
> >my solution:
> 
> >file * | grep 'shell script text executable' | cut -f1 -d':' | xargs
> 
> >head -n 3
> 
> This is the first time I've seen the xargs command. It's quite handy!
> 
> Berenice