This can't work, because the first \1 will be always set to the last match ahead (and undef or "" at first encounter)

This is because $1 is a global var will keep match instead of erasing when backtracking.

FWIW I tried something similar by capturing the following character in $2 for the next run:

m/ ^ (?:(?!\2).)*? (.) (?=(.|$)) (?!.*\1) /x

But couldn't get it to work, probably because the regex engine is not considering another defined \2 while backtracking. (or probably b/c I was too tired last night)


  DB<310> @inp = glob '{a,b}'x3


  DB<311> ;m/ ^ (?:(?!\2).)*?  (?{say "<$_ $2>"})  (.) (?=(.|$)) (?!.*
+\1) /x and say ("found $1 in $_") for @inp
<aaa >
<aab >
<aba >
<aba b>
found b in aba
<abb >
found a in abb
<baa >
found b in baa
<bab >
<bab a>
found a in bab
<bba >
<bbb >


  DB<312>

[download]

probably I'm having a bug in my logic, experts to the rescue! ;-)

Didn't have the time yet for proper debugging.

Cheers Rolf
(addicted to the Perl Programming Language and ☆☆☆☆ :)
Je suis Charlie!

In reply to Re^2: Regex: matching character which happens exactly once (using global memory) by LanX
in thread Regex: matching character which happens exactly once by LanX

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