The lack of any filesystem interaction notwithstanding, your mistake is in comparing 2 regexen rather than matching a string. Here's an amended version of your script showing the match actually happening.

#!/usr/bin/env perl 

use strict;
use warnings;
use diagnostics;

my $regex = qr/carlos\.txt/;
my $file  = 'juan_carlos.txt';

if (defined ($file) && ($file =~ $regex)) {
    print "File $file matched\n";
} else {
    print "File $file not matched\n";
}
[download]

I've named the variables appropriately. Note that there's nothing in this script to say that $file is anything to do with the filesystem (yet) - the variable just has a semantic name.

you might be interested in the module File::Find , it's core and has plenty of examples in the documentation.

HTH :)

Nothing in your script does any sort of operation on the filesystem. Not to mention you're comparing the string representation of a regular expression against the same regular expression (which isn't really going to do anything useful; or again, do anything against the filesystem).

If, as it appears, you are trying to find a file with a fixed name rather than a group of files with a common part to their name, no regexp is required. Just perform a string comparison on the filename.

 if ($file eq 'carlos.txt')

This script will list everything in the directory where the script is located and point out the file named 'carlos.txt'

use strict;

my $file;

# Read the current directory into an array
opendir(my $dir, '.');
my @files = readdir($dir);
closedir ($dir);

# Iterate over array to file file
foreach $file(@files) {
    print "$file";
    if ($file eq 'carlos.txt') {
        print "  <------------- Found File";
    }
    print "\n";
}
[download]

For filtering lists grep is often used:

use warnings;
use strict;

opendir(my $dir, '.');
my ($file) = grep {$_ eq 'carlos.txt'} readdir($dir);
closedir ($dir);

print "$file <------------- Found File\n" if $file;
[download]

Optimising for fewest key strokes only makes sense transmitting to Pluto or beyond

Yes indeed - much nicer and much more Perl-ish!

I deliberately didn't write it that way though so that CarlosN could (hopefully) understand what is going on.