Ok, well both of these have the same affect:

my $string = "foo bar testing";
my $string2 = "foo bar testing";

use Benchmark;
use Test;

####################
# Test 1
####################
my $start = new Benchmark;
    
Test::testing1($string);
print qq|String is now: $string \n|;
    
my $end = new Benchmark;
my $diff = timediff($end, $start);
print "Time taken was ", timestr($diff, 'all'), " seconds \n\n"; 

####################
# Test 2
####################
# start timer
my $start = new Benchmark;
    
$string2 = Test::testing2($string2);
print qq|String2 is now: $string2 \n|;
    
my $end = new Benchmark;
my $diff = timediff($end, $start);
print "Time taken was ", timestr($diff, 'all'), " seconds \n\n";
[download]

However, if I change the $string and $string2 to:

my $string = "sf osfpsid hfosidhf soifh sofihs foishfosihf soifh soifhsofihsfoihs foishf sofhfo ihsf oishfsoifhsf \n" x 1000000;

...then there is quite a considerable difference. The code in Test.pm is as follows:

package Test;

use strict;

sub testing1 {
  print "At testing1 \n";
  $_[0] =~ s/foo/test/g;
}

sub testing2 {
  print "At testing2 \n";
  my $string = $_[0];
  $string =~ s/foo/test/g;
  return $string;
}

1;
[download]

Judging from the above then - I'm guessing just editing $_[0] directly is gonna be the best option for us, as it seems to be a lot quicker.

Cheers

Andy