use strict;

my $string = 'ri\d+';

while (my $line = <>) {
    if ($line =~ m{ ( ( \Q$string\E ){3} ) }xms) {
        print $line;
        printf qq{\tMatched "$2" x 3: "$1"\n};
    }
}
[download]

Why don't you post a little more of your code "calling some files"?