Perl standard deviation

First of all, yes there is a module for this, but what fun is that. I needed to do a standard deviation calculation in a production system where we have a custom stripped down Perl and I did not have time to get change control for installing a new RPM. I don't need change control to have my own Perl script in my home directory and it is so simple. Also I love writing math code, when ever possible I try to use a bit mask test rather then big lists of if conditions.

Perl is one language that it bittersweet to me. It is very powerful, has endless ability, millions of modules that add every possible feature you could want. My only complaint is that it is so flexible that it creates the perfect environment for bad code habits. Most of the worst code I have ever seen was done in Perl, and some of it was my code.

Coding in Perl is fun and it is a very powerful tool. If you have not done any Perl coding you should give it a try. For now here is my simple code to calculate standard deviation.

#!/usr/bin/perl
use strict;

#Prevent division by 0 error in case you get junk data
exit undef unless(scalar(@ARGV));

# Step 1, find the mean of the numbers
my $total1 = 0;
foreach my $num (@ARGV)
{
        $total1 += $num;
}

my $mean1 = $total1 / (scalar @ARGV);

# Step 2, find the mean of the squares of the differences
# between each number and the mean
my $total2 = 0;
foreach my $num (@ARGV)
{
        $total2 += ($mean1-$num)**2;
}
my $mean2 = $total2 / (scalar @ARGV);

# Step 3, standard deviation is the square root of the
# above mean
my $std_dev = sqrt($mean2);
printf "%0.2f", $std_dev;