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That's because of the /g switch in the first match.From perlop:
The "/g" modifier specifies global pattern matching--that is, matching as many times as possible within the string. How it behaves depends on the context. In list context, it returns a list of the substrings matched by any capturing parentheses in the regular expression. If there are no parentheses, it returns a list of all the matched strings, as if there were parentheses around the whole pattern.

In scalar context, each execution of "m//g" finds the next match, returning true if it matches, and false if there is no further match. The position after the last match can be read or set using the pos() function; see "pos" in perlfunc. A failed match normally resets the search position to the beginning of the string, but you can avoid that by adding the "/c" modifier (e.g. "m//gc"). Modifying the target string also resets the search position.

Aha. In scalar context (boolean is scalar, and you are using the match in an if-expression) the /g matching returns the next match. So the match-operator keeps its state with regard to that match, and repeating the same match returns again the next match - and there is no more match. Failing the match the match-opreator gets reset. Consider:
use strict; use warnings; my $regexp = 'Perl Monks'; if($regexp =~ m/^Perl Monks/gi) { print "\nFound.."; } else { print "\nNot Found.."; } if($regexp =~ m/^Perl Monks/gi) { print "\nFound.1."; } else { print "\nNot Found.1."; } if($regexp =~ m/^Perl Monks/gi) { print "\nFound.2."; } else { print "\nNot Found.2."; } print "\n"; __END__ Found.. Not Found.1. Found.2.

--shmem

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}

In reply to Re: Re-use of a global match by shmem
in thread Re-use of a global match by gube

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