#!/your/perl/here

# find all palindrome phrases on each line
#     only phrases of two or more alpha
#     a phrase starts and ends on a word boundary
#
# nested palindrome phrases will also be found
# (including single words)

use strict;
use warnings;
our $N;

my $re = 
  qr/(                         # start $1
      \b                       # left word edge
      ([a-z].*[a-z])           # at least 2 alpha
      \b                       # right word edge 
      (??{                     # start code
          local $N = lc $^N;   # save capture
          $N =~ tr!a-zA-Z!!dc; # remove non-alpha
                               # fail if not pal
          '(?!)' if (lc($N) ne reverse lc($N));
         })                    # end code
     )                         # end $1
    /ix;

while (<DATA>)
{
  my $found;
  while ( /$re/g )
  {
    print "line $.:\n" unless $found;
    pos = pos() - length($1);  # find nested pals
    print "(",pos,") \"$1\"\n";
    $found = 1;                # \n between groups
    pos = pos() + 1;           # advance one
  }
  print "\n" if $found;
}

exit;

__DATA__
god dog
alpha beta gamma stop pots wonka wonka wonka
bookkeeper raisinhead
what is a bookkeeper pop repeekkoob tomorrow?
boob tube A man, a plan, a canal, Panama! kook peep aha
aba abba abbba aabbbaa abbba abba aba

##</code><code>##

__OUTPUT__
line 1:
(0) "god dog"

line 2:
(17) "stop pots"

line 4:
(10) "bookkeeper pop repeekkoob"
(21) "pop"

line 5:
(0) "boob"
(10) "A man, a plan, a canal, Panama"
(42) "kook"
(47) "peep"
(52) "aha"

line 6:
(0) "aba abba   abbba   aabbbaa abbba abba aba"
(4) "abba       abbba   aabbbaa abbba abba"
(10) "abbba     aabbbaa abbba"
(17) "aabbbaa"
(25) "abbba"
(31) "abba"
(36) "aba"