What have you tried? There is a neat trick you can use in Perl to make it easy to mock up a few files that may help you get started on a solution. Consider:

use strict;
use warnings;

my $file1Str = <<FILEDATA;
Alex 3 44
Barry 2 44
James 6 45
Drew 9 43
Alex 124 175
FILEDATA

my $file2Str = <<FILEDATA;
James 1 22
Alex 89 120
Alex 134 155
Barry 12 24
FILEDATA

my $file3Str = <<FILEDATA;
Alex 154 174
James 29 45
Drew 19 54
Drew 139 154
FILEDATA

open my $fileIn, '<', \$file1Str;
print "Prim: $_" for <$fileIn>;
close $fileIn;

for my $secFile ($file2Str, $file3Str) {
    open my $secIn, '<', \$secFile;
    print "Sec: $_" for <$secIn>;
}
[download]

Prints:

Prim: Alex 3 44
Prim: Barry 2 44
Prim: James 6 45
Prim: Drew 9 43
Prim: Alex 124 175
Sec: James 1 22
Sec: Alex 89 120
Sec: Alex 134 155
Sec: Barry 12 24
Sec: Alex 154 174
Sec: James 29 45
Sec: Drew 19 54
Sec: Drew 139 154
[download]

The trick is using a string as an input file by passing a reference to it in place of a file name in the open statement. That allows you to easily include several tests "files" in your source code so you can easily play around with test data. It also makes it really easy for us to reproduce your results when you ask a question concerning your code.