The extended default mechanism has been introduced to help selecting a module when only the first numbers in its version are specified. Starting portion of the version, part separated from the rest of the version string by a . character, could be used to refer to a more precise version number.

This mechanism is activated through the new configuration option extended_default. It enables to refer to a module named foo/1.2.3 as foo/1.2 or foo/1:

$ module config extended_default 1
$ module load -v foo/1
Loading foo/1.2.3

When multiple versions match partial version specified and only one module should be selected, the default version (whether implicitly or explicitly defined) among matches is returned. The following example shows that foo/1.1.1, the foo module default version, is selected when it matches query. Elsewhere the highest version (also called the latest version or the implicit default) among matching modules is returned:

$ module av foo
--------------- /path/to/modulefiles ---------------
foo/1.1.1(default)  foo/1.2.1  foo/1.10
foo/1.1.10          foo/1.2.3
$ module load -v foo/1.1
Loading foo/1.1.1
$ module purge
$ module load -v foo/1.2
Loading foo/1.2.3
$ module purge
$ module load -v foo/1
Loading foo/1.1.1

In case implicit_default option is disabled and no explicit default is found among matches, an error is returned:

$ module config implicit_default 0
$ module load -v foo/1.2
ERROR: No default version defined for 'foo/1.2'

When it is enabled, extended default applies everywhere a module could be specified, which means it could be used with any module sub-command or any modulefile Tcl command receiving a module specification as argument. It may help for instance to declare dependencies between modules:

$ module show bar/3
----------------------------------------------------------
/path/to/modulefiles/bar/3.4:

prereq      foo/1.2
----------------------------------------------------------
$ module load --auto bar/3
Loading bar/3.4
  Loading requirement: foo/1.2.3

Extended default activation can be controlled at configure time with the --enable-extended-default option. This option could be superseded with the MODULES_EXTENDED_DEFAULT environment variable, which could be set through the config sub-command with the extended_default option.

This new feature is available in git repository and will be included into the upcoming v4.4 release.

Please note that the extended default feature has been introduced first in Lmod, The other environment module system, some months ago. Having this very nice interface improvement also supported here will help people to get a similar module experience whether the module implementation installed. This feature is also for Modules a stepstone toward the advanced module version specifier feature that I will detail soon.