A possible solution for the sign.pl program is as follows:

sign.pl

#!/usr/bin/perl
 
# sign.pl - solution for exercise
 
use warnings;
use strict;
 
my $number;
 
print "enter a number: ";
 
$number = <>;
 
if ($number < 0)
{
    print "Your number is negative\n";
}
elsif ($number > 0)		# use "elsif" here
{
    print "Your number is positive\n";
}
else				# not positive or negative
{
    print "Your number is zero\n";
}
 
# note that a non-numeric entry will be interepreted as zero