sort results in ascending order

[Chris Stinemetz]

I would like to print results in ascending order starting with $cell, $sect, 
and finally $carr.

I am getting the error:

Name "main::a" used only once: possible typo at ./DOband.pl line 6.
Name "main::b" used only once: possible typo at ./DOband.pl line 6.

Below is my code. Any help is greatly appreciated.

Thank you,

#!/usr/bin/perl

use warnings;
use strict;

sub num {$a <=> $b;}

while (<>)
{
   chomp;
   if (/;/)
   {
     my @data = split /;/;
     my($cell,$sect,$carr,$RTD) = ($data[31],$data[32],$data[38],$data[261]);

     print "$cell\t $sect\t $carr\t $RTD\n";
   }
}

Chris