in reply to Regex help

You want capture and lookahead, print $2, $/ while /(\b\w+\b)(?=(.*?)\1)/g; \1 there is the form of backreference needed in regexen.

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Re: Re: Regex help
by bmann (Priest) on Jan 30, 2004 at 00:01 UTC
    Very cool, but the output of print $2, $/ while /(\b\w+\b)(?=(.*?)\1)/g; is:

     brown fox jumped over the other
 fox jumped over the other quick
 jumped over the other quick brown
 o  #????

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    In order to pass over the "o" (from "the o_the_r") the backreference in the lookahead needs to be anchored to word boundaries, ie:

    print $2, $/ while /(\b\w+\b)(?=(.*?)\b\1\b)/g;

    Not to mention, what is the desired output if the string is "the one the two the"?

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Re: Re: Regex help
by ysth (Canon) on Jan 30, 2004 at 03:11 UTC
    I can't believe you missed out on this opportunity to wave (--) the magic wand variable ($|) to get only the odd or even elements of a list: 
    print grep --$|,($|||=1)&& /\b(\w+)\b(?=(.*?)\b\1\b)/g'

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      What the good lord does that code do? Or rather, how does it work? Whats the $|||=1 bit, etc?
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        That bit is just charging up the magic wand. It can just as well be a separate statement: 
        $| = 1;
print grep --$|, /\b(\w+)\b(?=(.*?)\b\1\b)/g'

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        To get even elements instead of odd elements, you just start with the magic wand in the other position: 
        print grep --$|,($|&&=0)|| /\b(\w+)\b(?=(.*?)\b\1\b)/g'

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        or: 
        $| = 0;
print grep --$|, /\b(\w+)\b(?=(.*?)\b\1\b)/g'

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        Why ||= and &&= instead of = is left as an excercise for the reader. Hope that clears things up for you :)
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