Try it without the () in your first regex. The RE engine has to do a bit of setup work every time it enters or leaves a capturing () set during its passage through the candidate string, so they add a lot of overhead.

Also, your "||" version isn't very fair, since the /est/ always matches, meaning the /\d/ test is never made. But it is interesting how much faster the "constant" match for est is as opposed to the match for est|\d.

Oh, and use Benchmark: 

#!/usr/bin/perl -w

use strict;
use Benchmark qw(cmpthese);

my $i=0;

sub capture {
    "test$i"=~/(est|\d)/;
}

sub noCapture {
    "test$i"=~/(?:est|\d)/;
}

sub noParens {
    "test$i"=~/est|\d/;
}

sub twoRegexen {
    "test$i"=~/est/ || "test$i"=~/\d/;
}

cmpthese(-3,
        {
            capture   => \&capture,
            noCapture => \&noCapture,
            noParens => \&noParens,
            twoRegexen => \&twoRegexen,
        }
     );

[download]
Results (with 5.6.1, I'm sure 5.8.0 would be somewhat different): 
$ perl testRegexen.pl
Benchmark: running capture, noCapture, noParens, twoRegexen, each for 
+at least 3
 CPU seconds...
   capture:  4 wallclock secs ( 3.18 usr +  0.00 sys =  3.18 CPU) @ 72
+8822.24/s (n=2320570)
 noCapture:  2 wallclock secs ( 3.10 usr +  0.01 sys =  3.11 CPU) @ 82
+7692.26/s (n=2576606)
  noParens:  4 wallclock secs ( 3.14 usr +  0.01 sys =  3.15 CPU) @ 87
+1936.55/s (n=2748344)
twoRegexen:  4 wallclock secs ( 3.41 usr + -0.00 sys =  3.41 CPU) @ 14
+78048.90/s  (n=5047537)
                Rate    capture  noCapture   noParens twoRegexen
capture     728822/s         --       -12%       -16%       -51%
noCapture   827692/s        14%         --        -5%       -44%
noParens    871937/s        20%         5%         --       -41%
twoRegexen 1478049/s       103%        79%        70%         --

[download]

--
Mike

Edit: Oops, when I added the noParens case I forgot to put it into the cmpthese call here, although I'd put it into my test script.

In reply to Re: RE performance by RMGir
in thread RE performance by Vennis

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