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Re: regex corrupting separate regex

by blokhead (Monsignor)
on Feb 12, 2010 at 22:20 UTC ( #822942=note: print w/ replies, xml ) Need Help??


in reply to regex corrupting separate regex

From perlop (under "Quote-like operators"):

The empty pattern //

If the PATTERN evaluates to the empty string, the last successfully matched regular expression is used instead. In this case, only the g and c flags on the empty pattern is honoured - the other flags are taken from the original pattern. If no match has previously succeeded, this will (silently) act instead as a genuine empty pattern (which will always match).

This is an odd "feature" of Perl, and it's very easy to get bitten by it in m/$pattern/. It's happened to me several times. Perhaps a good solution is m/(?:$pattern)/ or m/(?:)$pattern/ or something similar, so that the pattern is never empty.

Update:

$ perl -le 'print 1 if "foo" =~ /o/; print 2 if "asdf" =~ //' 1 $ perl -le 'print 1 if "foo" =~ /z/; print 2 if "asdf" =~ //' 2 $ perl -le 'print 1 if "foo" =~ /o/; print 2 if "asdf" =~ /(?:)/' 1 2

blokhead


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Re^2: regex corrupting separate regex
by boxofrox (Initiate) on Feb 13, 2010 at 01:22 UTC
    Thank you, blokhead. That's what I trying to find in perlre.

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