Re: Strange Occurrence in Substitution Statement

[Corion]

See Perlop on 'the empty pattern':

If the PATTERN evaluates to the empty string, the last successfully matched regular expression in the current dynamic scope is used instead

[choroba]

And a possible solution:

$fname =~ s/(?:$extra)//;

[roho]

Thank you for the possible solution Choroba! I tried it and it works. It looks like the non-capturing group prevents the last successfully matched regular expression from being used when the pattern is empty.

[LanX]

I think it's simpler, the pattern isn't empty, because (?:...) is always part of the pattern. Meta characters count too.

This idiom is meant to be used as s//something/ in complicated parsing, kind of inherited from sed/awk IIRC.

You should also be aware that a genuinely empty pattern IS always matching. In your case the replacement is just invisible because empty.

So I'd rather prefer to make this explicit and self documenting

• s/$extra// if $extra

  Nowadays I doubt there are more than a fraction of a percent of programmers knowing/using this feature.

  I'd really like to see a Perl version/feature to switch it off by default.

[roho]

Thank you for the reference and the explanation Corion!