in reply to A complex recursive regex,help

You don't need recursion. Just use the positive look back and look forward assertions which don't eat string. See perlman:perlre 

my $a = "x|xx|xx|xxxx|xx|xxx|xx|xx|x";
$a =~ s/(?<=\|)xx(?=\|)/x x/g;
print "[$a]\n";
__DATA__
[x|x x|x x|xxxx|x x|xxx|x x|x x|x]

[download]

You don't say what you want to do with the edge cases: 

$a = 'xx|xx|xx';
# should this be (use example above):
[xx|x x|xx]
# or should it be
[x x|x x|x x]
# in which case you will need to add an extra regex because you can't 
+have 
# variable width lookbacks. this regex just processes those edge cases
$a =~ s/^xx(?=\|)|(?<=\|)xx$/x x/g;
# combined with the first part gives you some real perl line noise
# if you want it all in a single regex
$a =~ s/^xx(?=\|)|(?<=\|)xx(?=\|)|(?<=\|)xx$/x x/g;

[download]

cheers

tachyon

s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print

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Re: Re: A complex recursive regex,help
by OM_Zen (Scribe) on Feb 06, 2003 at 18:53 UTC
    Hi Tachyon ,

          my $a = "x|xx|xx|xxxx|xx|xxx|xx|xx|x";
      $a =~ s/(?<=\|)xx(?=(\||$))/x x/g;

      # this is actually doing the regex edge cases too Tachyon

    [download]


[reply]
[d/l]

      Well *actually* it does not. Your test string does not *actually* contain the edge cases ( xx at the begining and end of the string):o) If your test string had contained the edge cases you would no doubt have noted the following failure case..... 

      my $a = "xx|xx|xx|xxxx|xx|xxx|xx|xx|xx";
$a =~ s/(?<=\|)xx(?=(\||$))/x x/g;
print $a;
__DATA__
xx|x x|x x|xxxx|x x|xxx|x x|x x|x x

      [download]

      Here is one way to fix your regex: 

      $a =~ s/(?<=\|)|^xx(?=(\||$))/x x/g;

# and here is a way using the zero width boundary assertion \b
# that will match | ^ or $ but also matches any non aphlanumeric 
# so would potentially fail on '|xx,xx|' type strings
# if they exist in practice as your real data is no doubt
# not really xx.....
$a =~ s/\bxx\b/x x/g;

      [download]

      cheers

      tachyon

      s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print

[reply]
[d/l]
[select]
Re: Re: A complex recursive regex,help
by OM_Zen (Scribe) on Feb 06, 2003 at 01:00 UTC
    Hi Tachyon ,

    
     my $a = "x|xx|xx|xxxx|xx|xxx|xx|xx|x";
     $a =~ s/(?<=\|)xx(?=\|)/x x/g;
     print "[$a]\n";

    [download]


    This is the backward and forward assertions that I needed ,man , I have to learn more on this ,man THANKS A BUNCH Tachyonfor the help
[reply]
[d/l]

      Glad to help. The only bummer is that you cna't have variable width lookbacks (positive or negative) like (?<=x*) or (?<!x*) You can have variable width look forward assertions though (?=x*) or (?!x*) ar OK.....

      cheers

      tachyon

      s&&rsenoyhcatreve&&&s&n.+t&"$'$`$\"$\&"&ee&&y&srve&&d&&print

[reply]
[d/l]
[select]
        Hi Tachyon ,

        The variable width lookup stuff , I realise that after your code and the limitations too, THANKS A BUNCH man
[reply]

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