Thank you very much. This will help me.
Can we perfom a match by first concating the 2 strings and then querying on it.

   my $left = "xfafasfsdfasdfasdsfFOOBAR";
   my $right = "FOOBAR4t11";
   # my $concat = "xfafasfsdfasdfasdsfFOOBARFOOBAR4t11";
   my $concat = $left,$right;
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I should be able to hold on to FOOBAR in a back reference so that I can do further manipulation.
I need it this way because I do not know the size of boundaries which will match and I would like to match the maximum characters possible to match.
After this match the two sub strings should be concatnated. this concatnated string will have a single copy of FOOBAR in the middle. like

   my $conc = "xfafasfsdfasdfasdsfFOOBAR4t11";
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now this concatnated string will need to matched with one more string let us say

   my $str3 = "AR4t11xysadgsfje";
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Now AR4t11 will match and the above process is repeated.
How efficient will this be if I have about sub strings of size about 500 each and I need to compare about 10000 such sequences with each other.

Thank you.
braj