Dear monks,

I'm trying to search for several regexes in some long files. To speed things up, I tried first checking a combined regex, to see if any of them matches the line. Like so:

my $comb=join('|',@ARGV);
while($line=<$infile>){
  if($line=~$comb){
    for $target(@ARGV){
      if($line=~$target){
        # do a thing
}}}}

[download]

This seems to speed things up, at least when the regexes are just plain words. But: If I try input regexes which are anchored ("^word"), then suddenly it's much slower! Is there some weirdness with alternations and anchors? Or did I make some obvious mistake?

(I could rewrite ^aaa|^bbb|^ccc as ^(aaa|bbb|ccc), but it might be that only some of the inputs are anchored.)

In reply to Alternations and anchors by Chuma

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