By curiosity :

This is perl, v5.8.8 built for x86_64-linux-gnu-thread-multi

#!/usr/bin/perl 
use strict;
use warnings;
use Regexp::Common qw /net/;
use Benchmark qw( cmpthese );

my $line = q{127.0.0.1}; 

cmpthese -10, {
    RE => '$line =~ /\A $RE{net}{IPv4} [|] password [|] (ssn=) \z/xmi'
+,

    RE_O => '$line =~ /\A $RE{net}{IPv4} [|] password [|] (ssn=) \z/xm
+io',

    ORIG => '$line =~ /[\d]{1,3}\.[\d]{1,3}\.[\d]{1,3}\.[\d]{1,3}\|pas
+sword\|(ssn=)/i',

    RE_CHAR => 'use charnames qw( :full);
                $line =~ /\A $RE{net}{IPv4}
                             \N{LINE TABULATION}
                             password
                             \N{LINE TABULATION}
                             (ssn=) \z/xmi'

};
[download]

             Rate    RE_CHAR   RE     RE_O    ORIG
RE_CHAR    17366/s      --     -2%     -2%   -100%
RE         17704/s      2%      --     -0%   -100%
RE_O       17747/s      2%      0%      --   -100%
ORIG    12717477/s  73132%  71732%  71561%      --
[download]

This example shows that the main speed difference is reall Regexp::Common, which does a bit more than just match \d{1,3}\.\d{1,3}\. ..:

$ perl -MRegexp::Common=net -wle 'print $RE{net}{IPv4}'
(?:(?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[
+0-1]?[0-9]{1,2})[.](?:25[0-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2})[.](?:25[0
+-5]|2[0-4][0-9]|[0-1]?[0-9]{1,2}))
[download]

The optimzation I talked about kicks in when the string is much longer, and the literal char occurs only once or twice. Then the literal is used as an anchor, thus reducing the need for backtracking.

#!/usr/bin/perl
use strict;
use warnings;

my $line = ('a' x 500) . 'b!' . ('a' x 20);

use Benchmark qw( cmpthese );

cmpthese -3, {
    literal => sub {$line =~ /a.{1,10}b!/ },
    class   => sub {$line =~ /a.{1,10}[b][!]/},
};
__END__
            Rate   class literal
class     3855/s      --    -99%
literal 712766/s  18390%      --
[download]

Update: added benchmark

Yes, it's interesting and i've made a few more tests to find some optimization.
See below :

#!/usr/bin/perl 
use strict;
use warnings;
use Benchmark qw( cmpthese );

my $line = ('a' x 500) . 'b!' . ('a' x 20);


cmpthese -10, {
    literal     => sub {$line =~    /a.{1,10}b!/ },
    literal_exp => sub {$line =~    /a(?>.{1,10})b!/ },
    literal_look => sub {$line =~   /a(?>.{1,10})(?<=b!)/ },
    class       => sub {$line =~  / [a]    .{1,10}  [b] [!] /x},
    class_exp   => sub {$line =~   / a     .{1,10}   b  [!] /x},
    class_back  => sub {$line =~   / a (?> .{1,10} ) b  [!] /x},
    class_back_look  => sub {$line =~  /  a (?> .{1,10} ) (?<=b[!]) /x
+},
    class_b  => sub {$line =~          /  a     .{1,10}   (?<=b[!]) /x
+},
};
[download]

                    Rate class_b  class class_back_look literal_look l
+iteral class_back literal_exp class_exp
class_b           2172/s      --   -53%            -72%         -75%  
+ -100%      -100%       -100%     -100%
class             4651/s    114%     --            -40%         -46%  
+  -99%       -99%        -99%      -99%
class_back_look   7809/s    259%    68%              --         -10%  
+  -99%       -99%        -99%      -99%
literal_look      8658/s    299%    86%             11%           --  
+  -99%       -99%        -99%      -99%
literal         640333/s  29376% 13666%           8100%        7296%  
+    --        -9%        -11%      -13%
class_back      704687/s  32338% 15050%           8924%        8039%  
+   10%         --         -2%       -4%
literal_exp     722209/s  33145% 15426%           9149%        8242%  
+   13%         2%          --       -2%
class_exp       733546/s  33667% 15670%           9294%        8373%  
+   15%         4%          2%        --
[download]

Thanks for your interest and your enlightment.


PooLpi

'Ebry haffa hoe hab im tik a bush'. Jamaican proverb