You could fix it in both places. I would definitely consider passing a global a bug.

May I also suggest an alternate implementation?

#!/usr/bin/perl

sub trim_start {
   for (my $s = @_ ? $_[0] : $_) {
      s/\A\s+//m;
      return $_;
   }
}

sub trim_end {
   for (my $s = @_ ? $_[0] : $_) {
      s/\s+\z//m;
      return $_;
   }
}

{
   my $test = 'abc , def';
   $test =~ /([\s\w]+),([\s\w]+)/;
   my @words = map trim_start,
               map trim_end,
               "$1", "$2";
}
[download]

The advantage of that implementation is that its flexible as to how its called.

• It can be used to trim a single value:

  print(trim_start(trim_end($var)), "\n");
  [download]

• It can be used to trim a list of values:

  my @trimed = map trim_start, map trim_end, @untrimmed;
  [download]