in reply to conditional expression testing

Checks if the numbered capturing buffer has matched something. 
 beri beri 
^,               then '(hana)' fails. Fail.

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 hana    bbs
^(hana)  (bbs),  then '\2' fails. Backtrack;
^(hana)\2,       then '\1' fails. Fail.

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(?(1)...) doesn't make any sense since it's impossible to match the regex without the first capture matching something. Did you mean (?(2)...)? 

'beriberi' =~ m#^(beri)(bbs)?(?(2)\2\1|\1)$#;

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 beri        beri
^(beri)(bbs)?\1  $   Match.

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'beribbsbbsberi' =~ m#^(beri)(bbs)?(?(2)\2\1|\1)$#;

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 beri  bbs   bbsberi
^(beri)(bbs)?\2 \1  $   Match.

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Update: Added working examples

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Re^2: conditional expression testing
by Anonymous Monk on Jun 01, 2010 at 16:35 UTC
    thank you guys. total misunderstanding on my part
    works perfectly now
    use warnings;
use strict;

my @dic = qw#beriberi hanabbsbbshana#;

for (@dic) {
   my $pat = $_;
   print "trying to match $pat\n";
   print "matched $pat\n" if $_ =~ m#^(hana)(bbs)?(?(1)\2\1|\1)$#;
}

my @pat = qw#AAAAG AC GC AZG ZC AAAG#;

for ( @pat ) {
   my $pat2 = $_;
   print "matching $pat2\n";
   print "matched $pat2\n" if $_ =~ m#[ATGC]+(?(?<=AA)G|C)$#;
}

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[d/l]
      m#^(hana)(bbs)?(?(1)\2\1|\1)$#;

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      is the same as 

      m#^(hana)(bbs)?\2\1$#;

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      since (?(1)...) is always true. And since you don't use the captures, that can be be simplified to 

      m#^hana(?:bbsbbs)?hana$#;

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[d/l]
[select]

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