Contrary to what my fellow Monks are telling, it is not always a good idea to join your single regex-patterns with |and then use this combined regex on all your tests. Alternations in a regex are processed in O(n) time so increasing the number of alternations has a linear effect on your processing time.

To start with if you do 

my $RE = join '|', <RECORDS>;

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and then later 
/$RE/;

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for every test, Perl will have to re-compile your pattern every time. It is much better to pre-compile the pattern, by doing 
my $RE = join '|', <RECORDS>;
my $compiled_RE = qr/$RE/;

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and then later 
/$compiled_RE/;

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In that case you only pay the compilation cost once.

Even better is it to use a module such as Regexp::Assemble which can automatically compile for you a more efficient regex. Cutting down on the number of alternations will lead to a faster regex. I tried this in a program of mine and by using Regexp::Assemble managed to get a 30% speed increase when using real world data.

CountZero

A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James

In reply to Re: Not sure what I am doing wrong by CountZero
in thread Not sure what I am doing wrong by learningperl01

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