I am reading perlretut, and g modifier and zero width look ahead assertion(?=) is what I am reading now... This is good example for me.

use warnings;
use strict;

my $str1 = q/It is a guide to action which ensures that the military a
+lways obey the commands of the party./;
my $str2 = q/It is a guide to action that ensures that the military wi
+ll forever heed Party commands is a guide./;

my $n=0;

while ( $str1 =~ /(?=(\S+\s+\S+\s+\S+))/g ) {
#while ( $str1 =~ /(\S+\s+\S+\s+\S+)/g ) { 
    my $t1 = $1;
    my $line="";

    while ( $str2 =~ /($t1)/g ) {
        $line .= $line eq '' ? '' : ',';
        $line.="str=$t1, $1($-[0])";
        $n++;
    }
    print "$line\n" if $str2 =~/$t1/;
}

print "No of matching is : $n\n";

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