#!/net/perl/5.10.0/bin/perl

use strict;
use warnings;

use 5.010_000;

my $string = 'This is perl, the Perl interpreter';

foreach my $flag ( '', 'i' ) {
    if ( my ($match) = $string =~ /(?$flag:(Perl))/ ) {
        print "$match\n";
    }
}
Perl
perl
__END__