Presidium Podium

Here is one thing you can do to speed up the performance of your Perl regular expression matching: use the /o operator.

By default, when you iterate through a loop and apply a regular expression repeatedly, Perl recompiles the regular expression internally every time:

while() {
        chomp;
        if(/^[a-zA-Z]+/) {
                …
        }

}

This is actually wise, as Perl makes no assumption about whether your pattern is dynamically generated. If it changes every time, the expression would require recompilation:

while() {
        chomp;
        my $pattern = get_upper_or_lower_pattern($_);
        if(/$pattern/) {
                …
        }
}

But if you’re using the same pattern over and over, you may want to apply the /o operator in order to have the expression compiled only once:

while() {
        chomp;

        if(/^[a-zA-Z]+/o) {
                …
        }
}

While my benchmarking suggests that the performance benefits are relatively negligible for a simple regex like the one above, they can be quite considerable for a pattern of greater complexity.

This entry was posted on Wednesday, January 23rd, 2008 at 6:57 pm and is filed under Development, Perl, Tips. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.