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

cmpthese( -2, {
    g => sub { 'network' =~ /^network$/g  },
    c => sub { 'network' =~ /^network$/gc },
    s => sub { 'networK' =~ /^networK$/   },
} );
__END__
       Rate    s    g    c
s 2106781/s   -- -28% -68%
g 2931188/s  39%   -- -56%
c 6602248/s 213% 125%   --
[download]

The /c modifier really boosts! Why? It doesn't reset the search position on a failed match while /g is in effect (see perlop). So it tests once from the beginning, and at each further invocation of the same match, it tests beginning at the end, failing quickly. With a single /g, every other match fails.

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}