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

pairs.pl

#!/usr/bin/perl
 
# pairs.pl - save a list of numeric pairs to a file
#
#  Write to the file "squares.dat" a list.  Each line
#  will contain a number (i) and the square of that number.
#  The starting and ending number will be specified as user
#  input.
 
use warnings;
use strict;
 
my $out_filename = 'squares.dat';
 
my ($start, $end);
 
print "Enter starting value: ";
$start = <>;
 
print "Enter ending value: ";
$end = <>;
 
# check that $start <= $end
unless ($start <= $end)
{
    die "start value ($start) must come before end ($end)\n";
}
 
# open $out_filename for writing
open OUT, ">$out_filename"
    or die "open($out_filename) $!";
 
# make a loop ($i) from $start to $end
#  write $i and $i*$i to the file
foreach my $i ($start..$end)
{
    printf OUT "%3d %3d\n", $i, ($i * $i);
}
 
# close the file
close OUT;