If you prefer a simple specialised module over full-blown solutions like PDL or Statistics::R, you could use Statistics::LineFit (which is 27k pure Perl, without any external dependencies).

Here's a simple example, which computes intercept, slope and R² for one data set (100 x/y data points):

use Statistics::LineFit;

my $x = [ 1..100 ];
my $y = [ map $_*2, 11..110 ];

my $lfit = Statistics::LineFit->new();
$lfit->setData($x, $y);

printf "a=%.4f, b=%.4f,  R2=%.4f\n", $lfit->coefficients(), $lfit->rSq
+uared();


# which outputs:  a=20.0000, b=2.0000,  R2=1.0000
[download]

( Looking at the input data, it's not too surprising that the R² is exactly 1.0 )

The module also allows to compute a number of related values, like residuals, standard error, etc. - in case you should need them.