You have many options. Let's assume you put your program specific modules in a directory lib/ below your current program directory.

The most common option is to use the lib pragma:

use lib 'lib';
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You can also do yourself what the lib pragma does:

BEGIN { unshift @INC, 'lib' };
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You can also change the environment variable that Perl looks at for additional include directories:

# in the shell script that starts your program:
PERL5LIB=/home/vvh/program/lib
export PERL5LIB
perl -w /home/vvh/program/program.pl $*
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Or you can start Perl with the -I parameter to specify the additional include directory:

# in the shell script that starts your program:
perl -w -I/home/vvh/program/lib /home/vvh/program/program.pl $*
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If this is for CGI scripts under Apache, and Taint isn't on, then you can set environment variables in your httpd.conf or .htaccess files, using the SetEnv directive. If your server setup allows it...

I don't even know which directive-type you'd have to allow, except that it definitely won't work if AllowOverride is set to "None". ("In this case, the server will not even attempt to read .htaccess files in the filesystem.")

Except when you turn -Taint on