Foreach is faster than map if you're modifying in place. If you're using foreach to push into an array, like what's happening here, then map is going to be faster. (which is why there's the recommendation not to use map if you're not doing anything with the list generated -- you might as well have just done foreach).

Update: benchmarks to show the speed differences between map, map reassigning to the original list, map in void context, for, and foreach. (if 'recent' is before 5.8.6, I don't think the optimizations worked)

purple:/tmp oneiros$ perl -version | head -2

This is perl, v5.8.6 built for darwin-thread-multi-2level
purple:/tmp oneiros$ perl timer.pl

100:
           Rate      map  new_map void_map      for  foreach
map      1089/s       --     -16%     -37%     -61%     -61%
new_map  1295/s      19%       --     -25%     -54%     -54%
void_map 1718/s      58%      33%       --     -38%     -39%
for      2793/s     156%     116%      63%       --      -1%
foreach  2825/s     159%     118%      64%       1%       --

500:
          Rate      map  new_map void_map  foreach      for
map      213/s       --     -14%     -35%     -60%     -60%
new_map  249/s      17%       --     -24%     -53%     -54%
void_map 328/s      54%      32%       --     -38%     -39%
foreach  526/s     147%     112%      61%       --      -2%
for      538/s     153%     116%      64%       2%       --

2500:
            Rate      map  new_map void_map      for  foreach
map       38.5/s       --     -15%     -38%     -61%     -61%
new_map   45.4/s      18%       --     -27%     -54%     -55%
void_map  61.9/s      61%      37%       --     -38%     -38%
for       99.5/s     158%     119%      61%       --      -0%
foreach  100.0/s     160%     120%      61%       0%       --
[download]

use warnings;
use strict;

use Benchmark qw(cmpthese);

my @counts = qw( 100 500 2500 );
my %templates = (
        map      => '@list = map { s/1//; $_ } @list;',
        new_map  => 'my @newlist = map { s/1//; $_ } @list;',
        void_map => 'map { s/1// } @list;',
        foreach  => 's/1// foreach @list;',
        for      => 's/1// for @list;'
);

my @tests = ();
while ( my ($name, $template) = each (%templates)) {
        my $test = <<EOF;
\$test = sub {
        my \@list = \@_;
        $template
}
EOF
        eval $test;
        foreach my $count (@counts) {
                $tests[$count]->{$name} = sub { &$test( 1 .. $count ) 
+};
        }
}

foreach my $count (@counts) {
        print "\n$count:\n";
        cmpthese( 500_000/$count, $tests[$count] );
}
[download]