Run this with ulimit -n 20, it works and has /etc/passwd open 100 times. Run with ulimit -n 10 and it will fail (due to stdio being open already).

openfiles.pl

#!/usr/bin/perl -w

for (1..10) {
    fork or open_files()
}

exit();

sub open_files {
    my @files = ();
    for (1..10) {
        open(my $fh, "/etc/passwd") or die "Unable to open: $!";
        push @files, $fh;
    }
    print("Files: @files\n");
    system("lsof -p $$");
    sleep();
}