#!/usr/bin/perl -w
my $string = "rid";
while (<>) {
if (/($string){3}/) {
print;
}
}

##</code><code>##

#!/usr/bin/perl -w

my $string = "rid";
while (<>) {
    if (/($string){3}/) {
        print;
    }
}

##</code><code>##

use strict;

my $string = 'ri\d+';
while (my $line = <>) {
    if ($line =~ m{ (?: \Q$string\E ){3} }xms) {
        print $line;
    }
}