push (my @hexnum, $hexnum);
    @hexnum = split ( ' ', $hexnum );

##</code><code>##

    $_ = <STDIN>;
    @hexnum = split;

##</code><code>##

sub go {
   my @esns = @_;
   ...
}

##</code><code>##

use English;

if (@ARGV and $ARGV[0] eq "-v") {
    shift;  # crude method for option handling (cf. Getopt::Std)
    print STDERR "ESN Converter v.02\n"; # report version when asked
}  # (otherwise, keep quiet about that)

unless (@ARGV and -r $ARGV[0]) { # if no file name, go interactive
    print STDERR "Usage: $0 [esn_list.filename]\n";
    $eof = ( $OSNAME =~ /.n.x$/ ) ? "^D" : "^Z";
    $prompt = "Please enter an ESN string (or $eof to exit): ";
    print STDERR $prompt;
}

while (<>) {
    s/\s+//g;  # start by eliminating all whitespace
    unless ( /^([0-9a-f]{2})([0-9a-f]{6})$/ ) {
       print STDERR "skipped input string $_ : not a valid ESN\n";
       next;  # only accept 8-digit hex strings
    }
    ($mfg,$serno) = (hex $1, hex $2);
    printf( "Hex: %s == Decimal: %d %d\n",$_,$mfg,$serno);
} continue {
    print STDERR $prompt if $prompt;
}