Did you try tr/a-zA-Z89//cd;? I would expect it to be much faster than s///.

Update - quick benchmark: 

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

my $str;
$str .= chr(rand( 96 ) + 32) for 1 .. 1000;
my $d;

sub trans { ($d = $str) =~ tr/a-zA-Z89 //cd; $d }
sub justg { ($d = $str) =~ s/[^a-zA-Z8-9 ]//g; $d }
sub ig    { ($d = $str) =~ s/[^a-z8-9 ]//ig; $d }
sub igplus{ ($d = $str) =~ s/[^a-z8-9 ]+//ig; $d }
sub gplus { ($d = $str) =~ s/[^a-zA-Z8-9 ]+//g; $d}
#print join "\n", trans, justg, ig, igplus, gplus;

cmpthese ( 100_000, {
        trans  => \&trans,
        justg  => \&justg,
        ig     => \&ig,
        gplus  => \&gplus,
        igplus => \&igplus,
        });
__END__
Output:
          Rate  justg     ig igplus  gplus  trans
justg   4442/s     --    -2%   -19%   -22%   -93%
ig      4529/s     2%     --   -18%   -20%   -92%
igplus  5499/s    24%    21%     --    -3%   -91%
gplus   5674/s    28%    25%     3%     --   -91%
trans  60168/s  1255%  1229%   994%   960%     --

[download]
I ran it with strings of 10 char, 100, then 1000. The longer the string, the bigger the difference between tr/// and s///.

In reply to Re^2: regex to remove all non a-z and spaces by bmann
in thread regex to remove all non a-z and spaces by coldfingertips

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