Do gube's original question and the fine answers above not point also to some optomization (a single instance in the symbol table of the two identical if...} clauses? Note that adding the third time thru, but using a variant if... (no 'g') produces a match there but then repeating the variant if...} finds no match in 4.

#!/usr/local/bin/perl
use strict;
use warnings;

my $regexp = 'Perl Monks';
my $regexp2 = 'Perl Monks is a wonderful place to visit'; # even if No
+de Reaper is sometimes a bit loud


if($regexp =~ m/^Perl Monks/gi) {
    print "\nFound.0.";
} else {
    print "\nNot Found.0.";
}

if($regexp =~ m/^Perl Monks/gi) {
    print "\nFound.1.";
} else {
    print "\nNot Found.1.";
}

if($regexp =~ m/^Perl Monks/i) {    # No 'g' 
    print "\nFound.2.";
} else {
    print "\nNot Found.2.";
}


if($regexp2 =~ m/^Perl Monks/gi) {  # 'g' is back, but different $var 
+being tested
    print "\nFound.3.";
} else {
    print "\nNot Found.3.";
}


if($regexp2 =~ m/^Perl Monks/gi) {  # second identical use of $regex2 
+and match
    print "\nFound.4.";
} else {
    print "\nNot Found.4.";
}
[download]

produces:

perl gube_g.pl

Found.0.
Not Found.1.
Found.2.
Found.3.
Not Found.4.
[download]