Perl – How to install local modules with the cpan tool

On Unix:

usually you start cpan in your shell:

$ cpan

and type

install Chocolate::Belgian

or in short form:

cpan Chocolate::Belgian

On Windows:

If you're using ActivePerl on Windows, the PPM (Perl Package Manager) has much of the same functionality as CPAN.pm.

Example:

$ ppm
ppm> search net-smtp
ppm> install Net-SMTP-Multipart

see How do I install Perl modules? in the CPAN FAQ

Many distributions ship a lot of perl modules as packages.

• Debian/Ubuntu: apt-cache search 'perl$'
• Arch Linux: pacman -Ss '^perl-'
• Gentoo: category dev-perl

You should always prefer them as you benefit from automatic (security) updates and the ease of removal. This can be pretty tricky with the cpan tool itself.

For Gentoo there's a nice tool called g-cpan which builds/installs the module from CPAN and creates a Gentoo package (ebuild) for you.

There are two types of site-packages directories, global and per user.

1. Global site-packages ("dist-packages") directories are listed in sys.path when you run:

   python -m site
   

   For a more concise list run getsitepackages from the site module in Python code:

   python -c 'import site; print(site.getsitepackages())'
   

   Note: With virtualenvs getsitepackages is not available, sys.path from above will list the virtualenv's site-packages directory correctly, though. In Python 3, you may use the sysconfig module instead:

   python3 -c 'import sysconfig; print(sysconfig.get_paths()["purelib"])'
   

2. The per user site-packages directory (PEP 370) is where Python installs your local packages:

   python -m site --user-site
   

   If this points to a non-existing directory check the exit status of Python and see python -m site --help for explanations.

   Hint: Running pip list --user or pip freeze --user gives you a list of all installed per user site-packages.

Practical Tips

• <package>.__path__ lets you identify the location(s) of a specific package: (details)

  $ python -c "import setuptools as _; print(_.__path__)"
  ['/usr/lib/python2.7/dist-packages/setuptools']
  

• <module>.__file__ lets you identify the location of a specific module: (difference)

  $ python3 -c "import os as _; print(_.__file__)"
  /usr/lib/python3.6/os.py
  

• Run pip show <package> to show Debian-style package information:

  $ pip show pytest
  Name: pytest
  Version: 3.8.2
  Summary: pytest: simple powerful testing with Python
  Home-page: https://docs.pytest.org/en/latest/
  Author: Holger Krekel, Bruno Oliveira, Ronny Pfannschmidt, Floris Bruynooghe, Brianna Laugher, Florian Bruhin and others
  Author-email: None
  License: MIT license
  Location: /home/peter/.local/lib/python3.4/site-packages
  Requires: more-itertools, atomicwrites, setuptools, attrs, pathlib2, six, py, pluggy