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I have a string that begins with a variable sequence of characters, which is followed by a constant string that can be used as a unique anchor. I want to strip off the variable stuff at the beginning so that it begins with the anchor. For example, given this:

my $s = 'variable chars anchor want this';
I want to end with this:
$s = 'anchor want this';

I can think of several ways to approach this, but I do not know which might be considered better than others from the standpoint of style or efficiency (not just benchmarking, but also including potential for backtracking). These approaches include:

  • Capture the wanted portion
  • if( $s =~ m/^.*?(anchor.*)$/ ){ $s = $1; }
  • Capture and strip the variable portion
  • if( $s =~ m/^(.*?)anchor/ ){ my $bad = $1; $s =~ s/$bad//; }
    $s =~ s/^.*?anchor/anchor/;
  • Silly constructs
  • e.g., loops that utilize reverse, chop, split, ...

All of these employ .* (except for the silly constructs, which are left as an exercise for the reader), but I am trying to avoid that idiom by thinking more carefully about my regexen (Death to Dot Star!). I suspect a better regex might be something like a negated character class, but for a group: "match everything from the start of the string that does not match the sequence of characters anchor".

How would you do this, and why?


In reply to Regex style and efficiency by bobf

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