package whatever;

sub log {
 # do logging 
}

sub calculate_something {
 # do calculations
}

return 1;  # Perl insists on this :-) 


##</code><code>##

#!/usr/bin/perl

# Tells Perl to look in current dir for modules, may not
# be necessary. 
unshift @INC, ".";

use whatever;  # the file must have .pm ext for 'use'

whatever::log("Log file entry"); 
$answer = whatever::calculate_something();