Beefy Boxes and Bandwidth Generously Provided by pair Networks
Pathologically Eclectic Rubbish Lister

Redundant regex ([0-9]{2} | [0-9] {2, 4})?

by Popcorn Dave (Abbot)
on Feb 26, 2009 at 22:35 UTC ( #746692=perlquestion: print w/ replies, xml ) Need Help??
Popcorn Dave has asked for the wisdom of the Perl Monks concerning the following question:

Fellow monks,

I was surfing around Yahoo Answers the other day and a person was asking for an explanation of what the following regex did:

s/^\[[0-9]{2}-[0-9]-{2}-([0-9]{2} | [0-9] {2, 4})\]\s+//;

Of course I pointed him towards YAPE::Regex and presented him with the explanation output, but what struck me as odd was the

([0-9]{2} | [0-9] {2, 4})

Unless I'm mistaken, you're matching 2 numbers or between 2 and 4 numbers. Why would use the | there? If you're matching between 2 and 4 numbers you're matching 2 already aren't you? Am I just missing something here?

To disagree, one doesn't have to be disagreeable - Barry Goldwater

Comment on Redundant regex ([0-9]{2} | [0-9] {2, 4})?
Select or Download Code
Replies are listed 'Best First'.
Re: Redundant regex ([0-9]{2} | [0-9] {2, 4})?
by ikegami (Pope) on Feb 26, 2009 at 22:42 UTC

    No, /[0-9]{2} / does not match a subset of what / [0-9] {2, 4}/ matches.

    /[0-9]{2} / only matches "99\x{20}", where 9 can by any digit 0-9
    / [0-9] {2, 4}/ only matches "\x{20}9\x{20}{2,\x{20}4}", where 9 can by any digit 0-9

    Update: Fixed copy and paste bug in in second item.

      Holy crap, I need glasses! I completely missed the space in there and didn't realize it until I increased the font size.

      That makes perfect sense now. Duh.

      To disagree, one doesn't have to be disagreeable - Barry Goldwater

        Spaces removed, /[0-9]{2}/ does match a subset of what /[0-9]{2,4}/ matches.

        I'm sure what he wanted was just /[0-9]{2,4}/.

Log In?

What's my password?
Create A New User
Node Status?
node history
Node Type: perlquestion [id://746692]
Approved by Corion
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others contemplating the Monastery: (7)
As of 2015-11-25 07:08 GMT
Find Nodes?
    Voting Booth?

    What would be the most significant thing to happen if a rope (or wire) tied the Earth and the Moon together?

    Results (672 votes), past polls