I checked the secondary files against the primary file (analyse subroutine), rather than the other way around. Easy enough to switch that:

use Modern::Perl;

use Number::Range;
use Text::CSV::Auto qw( process_csv );
use Data::Dump qw /dump/;

my $debug = 0;
my %database;
process_csv('./primary.txt',
    sub {
        my $row = shift;
        push @{$database{$row->{name}}}, [$row->{start}, $row->{end}];
    }
);
say dump(\%database) if $debug;

analyse ('./secondary_1.txt');
analyse ('./secondary_2.txt');

sub analyse {
    my $file = shift;
    say "--Checking $file--";
    my %data;
    process_csv($file,
        sub {
            my $row = shift;
            push @{$data{$row->{name}}}, [$row->{start}, $row->{end}];
        }
    );
    say dump(\%data) if $debug;
    for my $name (sort keys %database) {
        unless ($data{$name}) {
            for my $range_ref (@{$database{$name}}) {
                say "$name: $range_ref->[0] $range_ref->[1]  absent 0 
+0";
            }
            next;
        }
        for my $range_ref (@{$database{$name}}) {
            print "$name: $range_ref->[0] $range_ref->[1] ";
            my $range = Number::Range->new($range_ref->[0] .. $range_r
+ef->[1]);
            for my $testrange_ref (@{$data{$name}}) {
                if ($range->inrange(@$testrange_ref)) {
                    print "present $testrange_ref->[0] $testrange_ref-
+>[1] ";
                }
                else {
                    print "absent 0 0 ";
                }
            }
            print "\n";
        }
    }
    say '------------------------------';
}
[download]

--Checking ./secondary_1.txt--
Alex: 3 44 absent 0 0 absent 0 0 
Alex: 124 175 absent 0 0 present 134 155 
Barry: 2 44 present 12 24 
Drew: 9 43  absent 0 0
James: 6 45 absent 0 0 
------------------------------
--Checking ./secondary_2.txt--
Alex: 3 44 absent 0 0 
Alex: 124 175 present 154 174 
Barry: 2 44  absent 0 0
Drew: 9 43 present 19 54 absent 0 0 
James: 6 45 present 29 45 
------------------------------
[download]

The whole range checking is done thanks to the Number::Range module. Please, check out its documentation and more specifically the inrange-method called in scalar context. I hand it the begin and endpoints of the range to be checked and if both are within the range to be checked against, it returns true, hence the whole range must be within.

The analyse subroutine in the script above takes as its only argument the filename of a "secondary" file and the primary file is checked against this secondary file. There is no secondary-against-secondary checking done or a reciprocal secondary against primary. Check the main for-loop inside this subroutine: it uses the data in the %database-hash which has been populated with the data from the primary file.

Dear CountZero,

Thanks for the modifications you've made to your script, and so promptly, I am quite thankful to you

The one thing I suppose that is still a little different from the output I'd first described is that for each row of the primary input file, I want in the output, additionally, ONLY 3 additional columns for EACH secondary input file.

So if there are 3 secondary files, that would be 3*3=9 additional columns added per every row of the primary file. If there are only 2 secondary files, add 2*3=6 additional columns per every row of the primary file. This will make a grid rather than a running list. The grid is way easier to use, and also compatible with MS Excel that some other folks at work use...

The one thing that therefore has to be changed in this script is to quote 'absent 0 0' JUST ONCE if all instances in the secondary files are absent. And similarly, quote ONLY 'present $start $end' when there is a range match, and not to worry about including absent 0 0 IF there is a match within primary range

To make that rather abstract explanation above easier to understand, let me take your output example and change it to what I am hoping to get as the final output:

--Checking primary.txt to ./secondary_1.txt and .secondary_2.txt--

Alex: 3 44 absent 0 0 absent 0 0

Alex: 124 175 present 134 155 present 154 174

Barry: 2 44 present 12 24 absent 0 0

Drew: 9 43 absent 0 0 present 19 54

James: 6 45 absent 0 0 present 29 45

I think I did a pretty average job of describing the output in previous postings. Does this sort of make sense now?

Thanks in advance, once again, CountZero, and I will now look into learning the modules that you have referred me to in your earlier postings.

To make that rather abstract explanation above easier to understand, let me take your output example and change it to what I am hoping to get as the final output:

Awesome, next modify the program :p