> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
> Sent: Thursday, September 13, 2001 8:09 PM
> To: [EMAIL PROTECTED]; [EMAIL PROTECTED]
> Subject: Re: to remove the file extension
>
>
> >>>>> "Jason" == Jason Tiller <[EMAIL PROTECTED]> writes:
>
> Bob> perl -e '-f $_ || print "Missing $_\n" for map
> {/^(.*)\.c$/; "$1.out"}
> Bob> @ARGV' *.c
>
> >> No. You've used $1 without verifying the match matched (in which
> >> case it would get the PREVIOUS match). For example, I can touch
> >> "foo\nbar.c" and run your script, and you'll get the wrong answer.
>
> Jason> What's wrong with this? Note that he's passing the
> *.c glob, so you'd
> Jason> expect to only find .c files in @ARGV, right? And if
> there're no *.c
> Jason> files in the current directory, then the script just
> prints nothing.
> Jason> Isn't that the correct behavior?
>
> He's matching /^.*\.c$/, which will fail to match
> "foo\nbar.c", although
> the glob will happily return that. Therefore, yes, there is precise
> specific input that will fail this.
>
> And in general, this is a bad idea anyway, hence my next rule:
>
> >> IMPORTANT RULE - Never ever ever use $1 except in a conditional
> >> context!!!
>
> Jason> That makes sense if you don't feel completely
> confident about your
> Jason> inputs... but all the time?
>
> Yes. All the time. As you can see, there's confidence that both you
> and he have in the input, and both of you have *unjustified*
> confidence, since I gave a counterexample that would break it.
>
> Therefore. ALL THE TIME. Program defensively.
Point well taken.
Here's a different approach that I think avoids that defect:
perl -e 's/c$/out/, -e $_ || print "Missing $_\n" for grep /\.c$/, @ARGV'
*
This has the advantage of accepting non-.c filenames as input, which are
silently ignored. However, I guess I am still assuming the substition will
always succeed, which is dependent on the form of the second regex (although
not on the input data, as far as I can tell. i.e. any file that makes it
through
the grep *will* be properly substituted, right?)
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