/^(([\w\d\-\_]+)[:,]|)(.*)$/

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An empty string should satisfy that regex. The second half, (.*) should obviously be satisfied by an empty string... and the first half (you may have to look a little) should also be fine on an empty string... (bunch-of-stuff|). Look at that... a bunch of stuff OR nothing at all. So, /^$nothing_ok$nothing_also_ok$/. Why on earth did that evaluate to FALSE on later perls is a better question! 
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:Wq
Not an editor command: Wq

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In reply to Re: regexp issue: Porting script from 5.6.1 to 5.005_02 by etcshadow
in thread regexp issue: Porting script from 5.6.1 to 5.005_02 by vladb

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