From the command line:

% perl -Mblib program [args…]
% perl -Mblib=DIR program [args…]

From your Perl program:

use blib; 
use blib 'DIR';

This pragma is intended primarily as a way of testing arbitrary Perl programs against an uninstalled version of a package through Perl's -M command-line switch. It assumes your directory structure was produced by the standard ExtUtils::MakeMaker module.

The pragma looks for a blib directory structure starting in the directory named DIR (or current directory if none was specified), and if it doesn't find a blib directory there, works its way back up through your ".." directories, scanning up to five levels of parent directory.