Frequently Asked Questions on Environment Modules

Module command

How does the module command work?

The command module is an alias for something like:


module ()
   eval `/some/path/modulecmd sh $*`


eval `/some/path/modulecmd csh !*`

Where the modulecmd outputs valid shell commands to stdout which manipulates the shell’s environment. Any text that is meant to be seen by the user must be sent to stderr. For example:

puts stderr "\n\tSome Text to Show\n"

I put the module command in a script and I run the script… it doesn’t change my environment?

A child process (script) can not change the parent process environment. A module load in a script only affects the environment for the script itself. The only way you can have a script change the current environment is to source the script which reads it into the current process.


. somescript


source somescript

How do I capture the module command output?

This ties in with the very first question. Since the module command is essentially an eval, the visible output to the screen must necessarily be sent to stderr. It becomes a matter on how to capture output from stderr for the various shells. The following examples just show how to spool the output from the avail command to a file. This also works for the various other module commands like list, display, etc. There are also various tricks for piping stderr to another program.


module avail 2> spoolfile

csh: (overwrite existing file)

module avail >&! spoolfile


I want the modulefile to source some rc script that came with some application

If you want to do this… you can, but that’s not what modules is all about. It is possible to have the modulefile output some text to stdout to source some script when loading. However, you lose the advantage of this tool, because you won’t be able to unload this environment. If you’re tempted to do this… don’t.

However, you can craft a modulefile by capturing the environment variables created or changed by the rc script. This is the goal of the and the utilities provided in the modules distribution:

/usr/share/Modules/bin/ somescript

You can also check out, which can translate the shell file into a modulefile and possibly reduce the amount of work needed to convert and maintain.

How do I specify the default modulefile for some modulefile directory?

Modules usually uses the the highest lexicographically sorted modulefile under the directory, unless there is a .version file in that directory which has a format like the following where “native” is a modulefile (or a sub-directory) in that directory. It’s also possible to set the default with a .modulerc file with a module-version command.

## version file for Perl
set ModulesVersion "native"

I don’t want a default modulefile for the directory?

Follow the same prescription as setting a default, but give some bogus value, say no_default. The module command will return an error message when no specific version is given.

Build Issues

The configure script complains about Tclx

checking for TclX configuration ( not found
checking for TclX version... using 8.4
checking TCLX_VERSION... 8.4
checking TCLX_LIB_SPEC... TCLX_LIB_SPEC not found, need to use --with-tclx-lib
checking TCLX_INCLUDE_SPEC... TCLX_INCLUDE_SPEC not found, need to use --with-tclx-inc

TclX is an optional library that can speed up some operations. You don’t need TclX for modules to compile and work, so you can add the –without-tclx option when configuring and it should proceed to completion. In fact, it should have succeeded anyways and just not attempt to use TclX.

Otherwise, you can load the TclX library package for your OS and the configure script should find it. If not then if you know where the file or the library and include files are placed then use the following options:

--with-tclx=<dir>       directory containing TclX configuration
                        ( [[searches]]
--with-tclx-ver=X.Y     TclX version to use [[search]]
--with-tclx-lib=<dir>   directory containing tclx libraries (libtclxX.Y)
--with-tclx-inc=<dir>   directory containing tclx include files
                        (tclExtend.h,...) [[none]]

Meta Information

Why does modules use Tcl?

The first versions of the Modules package used shell scripts to do its magic. The original authors then chose to implement the same in C to speed things up and to add features. At the time the only easily embeddable interpreter was Tcl which provided a standard language and the glue. Now that other interpreters are available they could be embedded, but haven’t so far. There is also a pure Tcl version available.

How can I help?

We can use help at various levels. The best way to contribute is to send in a patch file (see the FAQ on how to generate a patch file) with whatever fixes. The patch will be reviewed and tested. If you are a regular contributer then you’ll likely be invited to become a developer and to have direct source access, and the fame, power, and prestige that all entails.

How do I download the source repository?

Anonymously clone the git repository, view the list of branches, and set to a specific branch:

git clone git:// modules-myversion
cd modules-myversion
git branch -a
git checkout modules-3-X-Y
git status

How do I generate a patch file?

If you’re starting from a tarball

Unpack the tarball and it should place the sources into a directory named modules-3.X.Y , then rename the directory to modules-3.X.Y-myversion or something like that. Make whatever changes you want, and be sure to test the changes and if you can add tests to identify the bug and the fix… that will endear yourself to the developers.

Once you have the changes in your version, then unpack the original sources from the tarball in a directory side-by-side to the directory with your version, and at that parent level run the following diff command:

diff -u -r -P -N modules-3.X.Y modules-3.X.Y-myversion  > my.patch

If you’re starting from the git cloned repository:

From within the git repositories.

git diff > my.patch