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'

[download]
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'

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

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

In reply to Re: Re: Re: Re: Regex help by ysth
in thread Regex help by toonski

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