Perl package management#

Introduction#

(Note: the Perl community uses the term ‘modules’ rather than ‘packages’, however, in the documentation, we use the term ‘packages’ to try and avoid confusion with the module system for loading software.)

Perl comes with an extensive standard library, and you are strongly encouraged to use those packages as much as possible, since this will ensure that your code can be run on any platform that supports Perl.

However, many useful extensions to and libraries for Perl come in the form of packages that can be installed separately. Some of those are part of the default installation on VSC infrastructure.

Given the astounding number of packages, it is not sustainable to install each and everyone system wide. Since it is very easy for a user to install them just for himself, or for his research group, that is not a problem though. Do not hesitate to contact support whenever you encounter trouble doing so.

Checking for installed Perl packages#

To check which Perl packages are installed, the cpan utility is useful. It will list all packages that are installed for the Perl distribution you are using, including those installed by you, i.e., those in your PERL5LIB environment variable.

Load the module for the Perl version you wish to use, e.g.,
```
$ module load Perl/5.28.2-foss-2018a
```
Run cpan:
```
$ cpan  -l
```

Installing your own Perl packages#

Setting up your own package repository for Perl is straightforward. For this purpose, the cpan utility first needs to be configured. Replace the paths /user/leuven/301/vsc30140 and /data/leuven/301/vsc30140 by the ones to your own home and data directories.

Load the appropriate Perl module, e.g.,
```
$ module load Perl/5.28.2-foss-2018a
```
Create a directory to install in, i.e.,
```
$ mkdir $VSC_DATA/perl5
```
Run cpan:
```
$ cpan
```

Configure internet access and mirror sites:

cpan[1]> o conf init connect_to_internet_ok urllist

Set the install base, i.e., directory created above:
```
cpan[2]> o conf makepl_arg INSTALL_BASE=/data/leuven/301/vsc30140/perl5
```
Note that you can not use an environment variable for the path.

Set the preference directory path:

cpan[3]> o conf prefs_dir /user/leuven/301/vsc30140/.cpan/prefs

Commit changes so that they are stored in ~/.cpan/CPAN/MyConfig.pm, i.e.,
```
cpan[4]> o conf commit
```
Quit cpan:
```
cpan[5]> q
```

Now Perl packages can be installed easily, e.g.,

$ cpan IO::Scalar

Note that this will install all dependencies as needed, though you may be prompted.

To effortlessly use locally installed packages, install the local::lib package first, and use the following code fragment in Perl scripts that depend on locally installed packages.

use local::lib;