in reply to regex to remove all non a-z and spaces

EDIT: Testing with a 1000-character randomly generated string for 100000 iterations: $str =~ s/[^a-zA-Z8-9 ]//g; : 30 seconds
$str =~ s/[^a-z8-9 ]//ig; : 29 seconds
$str =~ s/[^a-zA-Z8-9 ]+//g; : 11 seconds

I wouldn't have expected the i flag solution to be more efficient, but there you go. There are significant savings from +. The most efficient regex therefore is: 

$str =~ s/[^a-z8-9 ]+//ig;

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EDIT: You're right, tr/// is much faster.

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Re^2: regex to remove all non a-z and spaces
by bmann (Priest) on May 16, 2005 at 04:09 UTC
    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///.
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[d/l]
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Re^2: regex to remove all non a-z and spaces
by coldfingertips (Pilgrim) on May 16, 2005 at 04:19 UTC
    This regex isn't exactly working for me. 
       $cleaned_search =~ s/[^a-z0-9 ]+//gi;

    [download]
    I keep getting files named "this+is a test.html", "the+farmer saves the day" and "i+hate this stuff.html".

    I thought it was the + so I removed it and the regex is still adding a + sign in my string when it wasn't there before. I also can't add any weird characters because it errors out when it tries to create the file. IE: if I used \ it said it failed to open on a closed filehandle or something.

    So it seems this regex isn't working at all.

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[d/l]

      There's no way that statement on its own would add a + sign.

      I think you need to give us a bit more context in order to find the cause of the problem: a few more lines of your code; what your input looks like; what your output looks like; and what you expect your output to look like...

      Then we'll be able to help you out, hopefully.

      s^^unp(;75N=&9I<V@`ack(u,^;s|\(.+\`|"$`$'\"$&\"\)"|ee;/m.+h/&&print$&
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