comment on

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

Are you posting in the right place? Check out Where do I post X? to know for sure.
Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
<code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>
Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
Want more info? How to link or How to display code and escape characters are good places to start.


Don't ask to ask, just ask
	PerlMonks