Welcome to the Environment Modules open source project. The Environment Modules package provides for the dynamic modification of a user's environment via modulefiles.
Typically users initialize their environment when they log in by setting environment information for every application they will reference during the session. The Environment Modules package is a tool that simplify shell initialization and lets users easily modify their environment during the session with modulefiles.
Each modulefile contains the information needed to configure the shell for an application. Once the Modules package is initialized, the environment can be modified on a per-module basis using the module command which interprets modulefiles. Typically modulefiles instruct the module command to alter or set shell environment variables such as PATH, MANPATH, etc. modulefiles may be shared by many users on a system and users may have their own collection to supplement or replace the shared modulefiles.
Modules can be loaded and unloaded dynamically and atomically, in an clean fashion. All popular shells are supported, including bash, ksh, zsh, sh, csh, tcsh, fish, as well as some scripting languages such as perl, ruby, tcl and python.
Modules are useful in managing different versions of applications. Modules can also be bundled into metamodules that will load an entire suite of different applications.
Here is an example of loading a module on a Linux machine under bash.
% module load gcc/6.1.1 % which gcc /usr/local/gcc/6.1.1/linux-x86_64/bin/gcc
Now we'll switch to a different version of the module
% module switch gcc gcc/6.3.1 % which gcc /usr/local/gcc/6.3.1/linux-x86_64/bin/gcc
And now we'll unload the module altogether
% module unload gcc % which gcc gcc not found
Now we'll log into a different machine, using a different shell (tcsh).
tardis-> module load gcc/6.3.1 tardis-> which gcc /usr/local/gcc/6.3.1/linux-aarch64/bin/gcc
Note that the command line is exactly the same, but the path has automatically configured to the correct architecture.
Flavours is a wrapper built on top of Modules C-version to simplify the organization and presentation of software that requiring multiple builds against different compilers, MPI libraries, processor architectures, etc. This package is written and maintained by Mark Dixon.
Env2 is a Perl script to convert environment variables between scripting languages. For example, convert a csh setup script to bash or the other way around. Supports bash, csh, ksh, modulecmd, perl, plist, sh, tclsh, tcsh, vim, yaml and zsh. This package is written and maintained by David C. Black.
Software Collections is a Red Hat project that enables you to build and concurrently install multiple RPM versions of the same components on your system, without impacting the system versions of the RPM packages installed from your distribution. Once installed a software collection is enabled with the scl command that relies on Modules for the user environment setup.
The NERSC - The National Energy Research Scientific Computing Center has a great introduction and help page: Modules Approach to Environment Management.