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Re^2: matching problem

by Athanasius (Monsignor)
on Feb 26, 2013 at 04:13 UTC ( #1020600=note: print w/ replies, xml ) Need Help??


in reply to Re: matching problem
in thread matching problem

Actually, I missed the definition of sub MatchLAC in the OP; my reply was directed solely at Re^2: matching problem. Mea culpa.

++AnomalousMonk for the excellent exposition! I didn’t know that the empty regex acts as a stand-in for the regex most recently matched (whether the match was successful or not). Is this documented anywhere? I’ve been looking through perlre, etc., but the only mention of the empty regex I’ve found so far relates to its use with split, where it means “split the string into individual characters.”

I guess overloading it makes sense, as a match that always succeeds isn’t much use. Are there any typical use cases for employing the empty regex to mean “repeat the regex used in the previous match”?

Athanasius <°(((><contra mundum Iustus alius egestas vitae, eros Piratica,


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Re^3: matching problem
by AnomalousMonk (Abbot) on Feb 26, 2013 at 20:49 UTC
    ... excellent exposition!

    Thank you very much!

    ... the empty regex acts as a stand-in for the regex most recently matched (whether the match was successful or not).

    In looking for empty pattern documentation (see below), I discovered this is not the case: "If the PATTERN evaluates to the empty string, the last successfully matched regular expression is used instead." (Strange what you can find when you actually read the docs!) Fixed my reply: thanks!

    Is this documented anywhere?

    The only place I've seen it is in perlop in the Regexp Quote-Like Operators section: the discussion of the  m// operator has a sub-section titled "The empty pattern //" (there's also a brief back-reference to it in the discussion of the  s/// operator).

    Are there any typical use cases for employing the empty regex to mean “repeat the regex used in the previous match”?

    My vague impression is this is something that evolved early-on as an emulation of shell usage or maybe from a desire for some kind of command line one-liner short-cut facility: saves typing, y'know. Offhand, I can't come up with a compelling example.

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