my $newstring = munge_string( 'one_two_three', '312' ); sub munge_string { my ( $string, $patternkey ) = @_; # patterns can also be 'text$1$2$3', etc my %patterns = ( 123 => '$1$2$3', 312 => '$3$1$2' ); # in reality the regex is also dynamic (based on $patternkey) $string =~ m/(\w+)_(\w+)_(\w+)/; return $patterns{$patternkey}; # want 'threeonetwo', got '$3$1$2' } #### $string =~ s/(\w+)_(\w+)_(\w+)/$patterns{$patternkey}/e; print $string; # '$3$1$2' #### $string =~ s/(\w+)_(\w+)_(\w+)/$3$1$2/; print $string; # 'threeonetwo' #### $string =~ s/(\w+)_(\w+)_(\w+)/join( '', $3, $1, $2 )/e; print $string; # 'threeonetwo'