#! /usr/bin/perl 
use strict;
my $s = 'aw --> Re   ';
my $subject = 'AW: Das AW ist AW nun AW mal AW eine AW Antwort :-)';
$s =~ /([^ ]*) *--> *([^ ]*)/;
my $what = $1; 
my $by = $2;
print "$subject\n";
$subject =~ s/$what/$by/i;
print "$subject\n";