HELP_MESSAGE() and exit unless $ARGV[1];

foreach (@ARGV) {
  HELP_MESSAGE() and exit unless /^-?\d+$/
}

##</code><code>##

use File::Basename;
# [unrelated code]
my $iam = basename $0;
# [unrelated code]

# Command-line
(my $x = shift) or die $syntax;
(my $y = shift) or die $syntax;

# Validity checking
($x =~ /^-?\d+$/) or die "$iam:  value $x not an integer\n";
($y =~ /^-?\d+$/) or die "$iam:  value $y not an integer\n";

##</code><code>##

HELP_MESSAGE() and exit unless $ARGV[1];

foreach (@ARGV) {
  HELP_MESSAGE() and exit unless /^-?\d+$/
}

my $start = shift @ARGV;
my $end = shift @ARGV;