Re: ls: avoiding error msg on non-existant file

Karl O. Pinc <[email protected]> [2002-11-28 22:41:18 -0600]:
> Well, there is a solution, but I don't like it much.

Hmm...  How about this suggestion below?

> Here's the task at hand.  My pwd contains
> files named 'uN' where 'N' is an integral version number.  I want
> the last version number, if there is one.  Here's my code:
> 
> last=$(for f in u* ; do
>          [ -e "$f" ] && echo "$f" ;
>        done | cut -c 2- | sort -n | tail -n 1 )

Functional.  But I see what you mean about it.

> (Except This is a translation into pure shell.
> I'm writing in php and using php's exec() (which is really system(3))
> instead of $() to produce the vaue for $last.  And the real
> code abstracts out the magic numbers like the 'u' and the number 2.
> FWIW, php's exec() has an implicit 'tail -n 1' built in.)

Ew.  I am well versed with perl but not php.  I hear they are deeply
related.  So for now I will stick with shell for the examples.

> Really, I'm in search of an idiom to take the result of shell's pattern
> expansion and pipe it somewhere, except the shell returns the pattern
> itself when there's nothing in the fs which matches and I want nothing
> at all in that case.

How about this as a possibility?  Still using 'ls'.  (I guess I could
have used 'echo * | tr " " "\012"' but I think this is more clear.)

It uses grep to extract only matching patterns, adjust to fit your
need.  I don't think any errors would normally occur and so none need
to be ignored.

  last=$(ls | grep -E '^u[0-9]+' | cut -c 2- | sort -n | tail -n 1)

> Oh well.  It's shell.  How elegent can it be made anyhow?

I actually like the shell quite a bit for many tasks.  The shell is
both powerful and weak at the same time.  The art is to play to the
strengths.

Bob