It's faster to use index() when looking for exact matches.

That ain't necessarily so, particularly when anchored: /^%%/ only needs to check the start of the string, whereas index($_, '%%') needs to scan to the first match, possibly through the entire string.

Update - of course using substr and eq is a much more obvious way to check this, and I've added some options to the code below to reflect that./Update

Try this:

#!/usr/bin/perl -w
use Benchmark qw/ cmpthese /;
my $count = shift;
our $a = '%%';
our $b = ' ' x 10000;
cmpthese($count, {
    first_re => q{ $match = "$a$b" =~ /^%%/ },
    last_re  => q{ $match = "$b$a" =~ /^%%/ },
    miss_re  => q{ $match = "$b"   =~ /^%%/ },
    first_index => q{ $match = index("$a$b", "%%") == 0},
    last_index  => q{ $match = index("$b$a", "%%") == 0},
    miss_index  => q{ $match = index("$b"  , "%%") == 0},
    first_substr => q{ $match = substr("$a$b", 0, 2) eq '%%' },
    last_substr  => q{ $match = substr("$b$a", 0, 2) eq '%%' },
    miss_substr  => q{ $match = substr("$b"  , 0, 2) eq '%%' },
})
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Hugo