look at perldoc perlre: 

       "(?<=pattern)"<br />
                 A zero-width positive look-behind assertion.
                 For example, "/(?<=\t)\w+/" matches a word that
                 follows a tab, without including the tab in $&.
                 Works only for fixed-width look-behind.

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In reply to Re^3: Pattern matching by reneeb
in thread Pattern matching by bedanta

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