http://www.perlmonks.org?node_id=487961


in reply to Slow Regex - How to Optimize

You code causes the regex to be recompiled each time round the inner loop. A slight rearrangement should improve things: 
foreach my $sub ( keys %SUBS ) {
    my $re = qr/[^a-zA-Z]$sub[^a-zA-Z]*\(/;
    foreach my $line ( @sub_code ) {
        if ( $line =~ $re ) { push( @subs, $key ) }
    }
}

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Dave.

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Re^2: Slow Regex - How to Optimize
by ikegami (Patriarch) on Aug 30, 2005 at 22:05 UTC

    That's not true. m/.../ only recompiles if the contents of any interpolated variable has changed. Demo:

    use re 'debug';

foreach (qw( abc abc def )) {
   print("==============================\n");
   print("$_\n");
   print("\n");
   /$_/;
}

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    Update: Oops, I didn't notice you reversed the loops in addition to moving the regexp.

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Re^2: Slow Regex - How to Optimize
by Anonymous Monk on Mar 11, 2016 at 14:14 UTC
    great post.. thanks a lot :) it really solved an issue here. reduced the runtime of a usecase from 30 minutes to ~10 seconds. hats off! :)
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