$file = "/path/to/file";

if (-s $file) {
    # file has non-zero size.
} else {
    # File is empty or does not exist.
}

##</code><code>##

$SIG{ALRM} = sub { die "Script took too long.\n" };
alarm(60);    # Create alarm signal in 60 seconds.
# ... do long-running stuff.
alarm(0);     # Cancel the alarm

##</code><code>##

END {
    unlink($tmpfile);
}