Convert file descriptor to file name in Linux

filename.pl

#!/usr/bin/env perl
use strict;
use warnings;

use File::Spec;

my @fhs;

opendir my $dh, '/etc';
for my $entry (readdir $dh) {
    my $file = File::Spec->catfile('/etc', $entry);
    next unless -f $file;

    open my $fh, '<', $file or next;
    push @fhs, $fh;

    last if @fhs > 20;
}

show_fd_names();
closedir $dh;

sub show_fd_names {
    opendir my $dh, "/proc/self/fd";
    for my $entry (readdir $dh) {
        my $file = File::Spec->catfile('/proc/self/fd', $entry);
        next unless -l $file;

        my $opened_file = readlink $file;
        print "fd=$entry => $opened_file\n";
    }
    closedir $dh;
}