It's impossible for those expressions to return nothing back.

It's impossible an expression to nothing back in scalar context.

If they return undef, then the pattern didn't match. Make sure $_ contains what you think it should.

If they return a zero-length string, it's because that's what they successfully matched.

In reply to Re^3: anonymous subroutines assigning regexes to hash keys by ikegami
in thread anonymous subroutines assigning regexes to hash keys by donkeykong

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