Perl modules may be installed using the CPAN module or from source.
CPAN method

perl -MCPAN -e shell (to get an interactive CPAN shell)
perl -MCPAN -e 'install Time::JulianDay' (if you know the name of the module, you can install it directly without interacting with the CPAN shell)

Within the CPAN shell:
i /expression/ will search for a Perl module containing expression, and
install module will install the module.

Example:
perl -MCPAN -e shell
i /JulianDay/
install Time::JulianDay

Note: if you are behind a firewall, you may wish to use passive FTP with Perl's Net::FTP module. Set the environment variable FTP_PASSIVE 1 (or any non-zero value) to use passive FTP when downloading Perl modules through CPAN.


Manual installation

To manually install a Perl module:

1. Download the Perl module from CPAN or other site.
2. Extract the tarball.
3. Run perl Makefile.PL
4. Run make
5. Run make test
6. Run make install

Note: you should use the same compiler to build Perl modules that you used to build Perl. For example, if you are building Perl modules with gcc and are using a version of Perl that was supplied with your distribution (ex. Solaris 8 includes Perl 5.005_03), you may run into errors.

Checking for existence of a Perl module
An easy way to check for the existence of a Perl module on your system (technically, in Perl's @INC array, a list of directories Perl searches when attempting to load modules) is to run perl -e 'use module;'

Example:

perl -e 'use HTML::Parser;'