Below is the code. I tried different lengths of strings (upper bound in 1..10000) and number of iterations (first argument to timethese). 
#!/usr/bin/perl

use strict;
use warnings;
use Benchmark qw/cmpthese timethese/;

my $y = join "", 1..10000;

my %tr;
@tr{map chr, 0..255} = map chr, 1..255,0;

my $tr = eval 'sub {$_[0] =~ tr/\x00-\xff/\x01-\xff\x00/r}';

my $trans = sub
{
  my $x = $y;
  $x =~ tr/\x00-\xff/\x01-\xff\x00/r;
};
my $subst = sub
{
  my $x = $y;
  $x =~ s/(.)/$tr{$1}/egr;
};
my $eval = sub
{
  my $x = $y;
  eval '$x =~ tr/\x00-\xff/\x01-\xff\x00/r';
};
my $preceval = sub
{
  my $x = $y;
  &$tr($x);
};

my $z = &$trans;

$z eq &$subst    or die;
$z eq &$eval     or die;
$z eq &$preceval or die;
length($y) == length($z) or die;

printf "length: %s\n", length($y);

timethese(0, {
  trans    => $trans,
  subst    => $subst,
  eval     => $eval,
  preceval => $preceval,
});

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In reply to Re^3: How to use a variable in tr/// by Anonymous Monk
in thread How to use a variable in tr/// by perl-novice

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