Can you try this version and see if any files are opened?

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

# my $fname = '.profile';
my $fname = 'MY_FILE';
my %users =  %{user_paths()};
for my $user (keys %users) {
    my $fh;
    if (open $fh, '<', "$users{$user}/$fname") {
        while (my $line = <$fh>) {
            if ($line =~ /BASE_PORT=(\d+)/) {
                print  "$user --> $1";
            }
        }
    }
    else {
        warn "couldn't open $users{$user}/MY_FILE $!";
    }
}

sub user_paths {
    my %users;
    open my $fh, '<', "/etc/passwd" || die "Can't Open : $!";
    while (<$fh>) {
        my @user = split (/:/);
        if ( $user[2] > 500 ) {
            $users{$user[0]} = "$user[5]";
        }
    }
    return \%users;
}
[download]

Cheers,
R.