How can I install specialized environments for different Perl applications?

Question

Is there anything equivalent or close in terms of functionality to Python's virtualenv, but for Perl?

I've done some development in Python and a possibility of having non-system versions of modules installed in a separate environment without creating any mess is a huge advantage. Now I have to work on a new project in Perl, and I'm looking for something like virtualenv, but for Perl. Can you suggest any Perl equivalent or replacement for python's virtualenv?

I'm trying to setup X different sets of non-system Perl packages for Y different applications to be deployed. Even worse, these applications may require different versions of the same package, so each of them may require to be installed in a separate module/library environment. You may want to do this manually for X < Y < 3. But you should not do this manually for 10 > Y > X.

Ideally what I'm looking should work like this:

perl virtualenv.pl my_environment
. my_environment/bin/activate
wget http://.../foo-0.1.tar.gz
tar -xzf foo-0.1.tar.gz ; cd foo-0.1
perl Makefile.pl
make install # <-- package foo-0.1 gets installed inside my_environment
perl -MCPAN -e 'install Bar' # <-- now package Bar with all its deps gets installed inside my_environment

Answer 1

Programs can modify what directories they check for libraries uwith use lib. This lib directory can be relative to the current directory. Libraries from these directories will be used before system libraries, as they are placed at the beginning of the @INC array.

I believe cpan can also install libraries to specific directories. Granted, cpan draws from the CPAN site in order to install things, so this may not be the best option.

Answer 2

I am not sure whether this is the same as that virtualenv thing you are talking about, but have a look for the @INC special variable in the perlvar manpage.

Answer 3

There's a tool called local::lib that wraps up all of the work for you, much like virtualenv. It will:

• Set up @INC in the process where it's used.
• Set PERL5LIB and other such things for child processes.
• Set the right variables to convince CPAN, MakeMaker, Module::Build, etc. to install libraries and store configuration in a local directory.
• Set PATH so that installed binaries can be found.
• Print environment variables to stdout when used from the commandline so that you can put eval $(perl -Mlocal::lib) in your .profile and then mostly forget about it.

Answer 4

What I do is start the CPAN shell (cpan) and install my own Perl 5.10 from it (I believe the command is install perl-5.10). This will ask for various configuration settings; I make sure to make it point to paths under /usr/local (or some other installation location other than the default).

Then I put its resulting location in my executable $PATH before the standard perl, and use its CPAN shell to install the modules I need (usually, a lot). My Perl scripts all start with the line

#!/usr/bin/env perl

Never had a problem with this approach.

Answer 5

I've used schroot for this purpose. It is a bit heavier than virtualenv but you can be sure that nothing will leak in that shouldn't.

Schroot manages a chroot environment for you, but mounts your home directory in the chroot so it appears like a normal shell session, just using the binaries and libraries in the chroot.

I think it may be debian/ubuntu only though.

After setting up the schroot, your script above would look like

schroot -c my_perl_dev
wget ...

See http://www.debian-administration.org/articles/566 for an interesting article about it

Answer 6

It looks like you just need to use the INSTALL_BASE configuration for Makefile.PL (or the --install_base option for Build.PL)? What exactly do you need the solution to do for you? It sounds like you just need to get the installed module in the right place. You've presented your problem as an XY Problem by specifying what you think is the solution is rather than letting us help you with your task.

See How do I keep my own module/library directory? in perlfaq8, for instance.

If you are downloading modules from CPAN, the latest cpan command (in App::Cpan) has a -j switch to allow you to choose alternate CPAN.pm configuration files. In those configuration files you can set the CPAN.pm options to install wherever you like.

Based on your clarification, it sounds like local::lib might work for you in single, simple cases, but I do this for industrial strength deployments where I set up custom, private CPANs per application, and install directly from those custom CPANs. See my MyCPAN::App::DPAN module, for instance. From that, I use custom CPAN.pm configs that analyze their environment and set the proper values to each application can install everything in a directory just for that application.

You might also consider distributing your application as a Task::. You install it like any other Perl module, but dependencies share that same setup (i.e. INSTALL_BASE).