Hi Rob,
Thanks for your reply.
On Sun, 04 Mar 2012 09:50:07 +0000
Rob Dixon <rob.di...@gmx.com> wrote:
> On 04/03/2012 07:56, Manfred Lotz wrote:
...
> >
> > Running this gives:
> >
> > Sub3: Issuing [uname -a]
> > Linux hogwart 3.0.0-14-generic-pae #23~lucid1-Ubuntu SMP Thu Dec 8
> > 15:03:12 UTC 2011 i686 GNU/Linux 0
> > Sub3: Issuing [date]
> > Sun Mar 4 08:54:18 CET 2012
> > 0
> > Use of uninitialized value $cmd in concatenation (.) or string
> > at ./foreach1.pl line 20.
> >
> > Sub1
> > 1
> > Use of uninitialized value $cmd in concatenation (.) or string
> > at ./foreach1.pl line 20.
> >
> > Sub1
> > 1
> >
> >
> > What am I doing wrong here?
>
> Hi Manfred
>
> You have discovered why many people say it is unsafe to use $_. $_ is
> a global variable, and the loop
>
> while (<$fh> ) { print; }
>
> modifies it, leaving it undefined at end of file. Unfortunately the
> loop
>
> foreach ( @cmds ) { say sub1($_); };
>
> has aliased $_ to each of the elements of @cmds, so the array is
> getting corrupted by the subroutine call.
>
Yep, I thought that $_ is somewhow a globally available lexical
variable.
> You can get around this either by using a named variable for reading
> from the pipe, or by adding
>
> local $_;
>
I would prefer then to not use $_ in the foreach loop but doing as Tim
suggested.
foreach my $v (@cmds) { somesub($v); };
My conclusion is now that only in really simple cases it is safe to use
$_ in a foreach loop.
Thanks again to you and Tim.
--
Manfred
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