top-priority-values.rst

Top priority environment variable values

Multiple modulefiles may alter the same environment variable. It may be wanted that among those modulefiles one should have the priority over the others and the value it sets should persist even if another modulefile loaded after attempts to alter the variable.

When using the setenv modulefile command, a top priority value should persist over later setenv tries. On append-path modulefile command, this top priority value should stay last position and for prepend-path modulefile command, value should stay first position.

Implementation

Top priority values are implemented by the use of a site-specific configuration that supersedes the definition of the setenv, append-path and prepend-path commands to introduce a --top argument. This argument enables a value set with this flag on to hold top priority and thus cannot be altered unless by another top priority value.

For append-path command, --top ensure value will stay at last position in path-like variable. Same goes for prepend-path where --top ensure first position in path-like variable.

../../example/top-priority-values/siteconfig.tcl

Compatible with Modules v4.2

Installation

Create site-specific configuration directory if it does not exist yet:

$ mkdir

Then copy there the site-specific configuration script of this recipe:

$ cp example/top-priority-values/siteconfig.tcl /

Note

Defined location for the site-specific configuration script may vary from one installation to another. To determine the expected location for this file on your setup, check the value of the siteconfig option on Modules version 4.3 or above:

$ module config siteconfig

On older version of Modules, check the modulecmd.tcl script:

$ grep '^set g_siteconfig ' $MODULES_CMD

Usage example

With a bar/1 modulefile that sets environment variables in a regular way:

../../example/top-priority-values/modulefiles/bar/1

And a foo/1 modulefile that sets the same variables than bar/1 but with the --top priority flag:

../../example/top-priority-values/modulefiles/foo/1

Enable the modulepath where the example modulefiles are located:

$ module use example/top-priority-values/modulefiles

Load foo/1 then bar/1 modulefiles and check value of the environment variable set:

$ module load foo/1 bar/1
$ echo $TESTVAR
topvalue
$ echo $TESTPATH
topprevalue:prevalue:postvalue:toppostvalue