$var = 'abc';
$var =~ s/b//; # $var is now 'ac'
$var =~ s/b//; # still 'ac' even before the s///
$var =~ s/b//; # yet another attempt to remove 'b' from 'ac'
$var =~ s/b//; # well, you get the point....
.... etc.

##</code><code>##

#!/usr/bin/perl -wT

use strict;

use Benchmark;
our $var;

$var = '\a\\aa\\\aaa\\\\aaaa'x100;

## rerun the original benchmarks to provide a baseline 
timethese(100000, {
    'old s'  => sub { $var =~ s/\\//g },
    'old tr' => sub { $var =~ tr/\\//d },
});

## try some new benchmarks that reinitialize $var each time
timethese(50000, {
    'new s'  => sub { $var = '\a\\aa\\\aaa\\\\aaaa'x100; $var =~ s/\\//g },
    'new tr' => sub { $var = '\a\\aa\\\aaa\\\\aaaa'x100; $var =~ tr/\\//d },
});

=OUTPUT
Benchmark: timing 100000 iterations of old s, old tr...
     old s:  1 wallclock secs ( 0.56 usr +  0.00 sys =  0.56 CPU) @ 178571.43/s (n=100000)
    old tr:  2 wallclock secs ( 1.23 usr +  0.00 sys =  1.23 CPU) @ 81300.81/s (n=100000)
Benchmark: timing 50000 iterations of new s, new tr...
     new s: 43 wallclock secs (30.81 usr +  0.02 sys = 30.83 CPU) @ 1621.80/s (n=50000)
    new tr:  3 wallclock secs ( 2.06 usr +  0.00 sys =  2.06 CPU) @ 24271.84/s (n=50000)