my $sequence_number = shift ||
    die "cinnamon: sequence number needed as argument\n";

open (ERROR, "/usr/bin/errpt -g -l $sequence_number |");

##</code><code>##

my $sequence_number = shift;
unless ($sequence_number =~ /^\d+$/) {
    # I am assuming it must be a number
    die "cinnamon: sequence number needed as argument\n";
}

open (ERROR, "/usr/bin/errpt -g -l $sequence_number |") || die "couldn't open errpt: $!";