New features
************

This document describes the major changes occurring between versions
of Modules. It provides an overview of the new features and changed
behaviors that will be encountered when upgrading.


v5.3
====


Module cache
------------

A module cache file can be created under each modulepath directory
with new "cachebuild" sub-command. Cache file is named ".modulecache"
and contains in one file all modulefiles and modulercs found in
modulepath directory.

When cache file is available, module search mechanism uses this file
rather walking through the content of modulepath directory. I/O
operations are saved this way which reduces search processing time.

When searching for available modules without cache, each file
contained in enabled modulepaths is opened to check if it is a
modulefile or not. Such checks lead to a large number of I/O
operations on large module setup like in the below example where a
total of 1051 modulefiles are available:

      $ module -o "" avail -t | wc -l
      1051
      $ syscall_list=access,close,getdents64,newfstatat,openat,read
      $ strace -f -e $syscall_list -c $MODULES_CMD bash avail
      % time     seconds  usecs/call     calls    errors syscall
      ------ ----------- ----------- --------- --------- ----------------
       31.09    0.003776           2      1424         9 openat
       28.56    0.003469           2      1649         3 newfstatat
       14.08    0.001710           1      1421           close
       11.85    0.001439           3       460           getdents64
       10.88    0.001321           0      1505           read
        3.54    0.000430           4       107         5 access
      ------ ----------- ----------- --------- --------- ----------------
      100.00    0.012145           1      6566        17 total

After building cache file for every enabled modulepaths in this
example setup, a lot of I/O operations are saved when searching for
available modules:

      $ module cachebuild
      Creating /path/to/modulefiles/.modulecache
      Creating /path/to/modulefiles.2/.modulecache
      Creating /path/to/modulefiles.3/.modulecache
      $ module config cache_buffer_bytes 1000000
      $ strace -f -e $syscall_list -c $MODULES_CMD bash avail
      % time     seconds  usecs/call     calls    errors syscall
      ------ ----------- ----------- --------- --------- ----------------
       70.19    0.000544           2       255           read
       13.16    0.000102           2        38         9 openat
        8.90    0.000069           1        35           close
        6.06    0.000047           1        31         2 newfstatat
        1.68    0.000013           1        11         2 access
      ------ ----------- ----------- --------- --------- ----------------
      100.00    0.000775           2       370        13 total

A significant execution time drop may be noticed, especially if
modulepath directories are stored on heavily loaded network
filesystem.

To further optimize I/O operation count, the "cache_buffer_bytes"
configuration option can be set like in the above example to use fewer
number of "read" operation to load cache file content.

To build cache file, user should be granted write access on modulepath
directory. Modulefiles or directories that are not accessible for
everyone are not recorded in cache. An indication is saved instead to
test these limited access elements when cache is loaded to determine
if they are available to currently running user.

Cache file can be ignored with "--ignore-cache" command line switch or
more permanently with "ignore_cache" configuration option.

Cache file is valid indefinitely by default but "cache_expiry_secs"
configuration option can be used to define the number of seconds a
cache file is considered valid after being generated. Expired cache
file is ignored.

Cache file of enabled modulepaths can be deleted all at once with
"cacheclear" sub-command.


Querying available module variants
----------------------------------

A new mechanism named Extra match search is introduced to evaluate
modulefiles during a module search to find those matching an extra
query on a variant value, a dependency or an environment variable
definition.

During this specific evaluation, modulefiles are interpreted in *scan*
mode to collect the different Tcl modulefile commands they use.
Special care should be given when writing modulefiles to ensure they
cope with such evaluation mode.

Extra match search mechanism is available on "avail", "whatis" and
"paths" sub-commands.

With this new mechanism, it is possible to list all available variant
defined in modulefiles with their associated values:

   $ module config avail_output modulepath:alias:dirwsym:sym:tag:key:variant
   $ module config variant_shortcut toolchain=%
   $ module avail
   --------------------- /path/to/modulefiles ---------------------
   bar/1.0{%a,b}  foo/1.0{%a}      qux/1.0{%a,b}
   bar/2.0{%b}    foo/2.0{%a,b,c}  qux/2.0{%b,c}

   Key:
   modulepath       {%value}={toolchain=value}
   default-version  {variant=value}

You can also search for modules defining a specific variant value:

   $ module avail %a
   --------------------- /path/to/modulefiles ---------------------
   bar/1.0{%a,b}  foo/1.0{%a}  foo/2.0{%a,b,c}  qux/1.0{%a,b}

   Key:
   modulepath       {%value}={toolchain=value}
   default-version  {variant=value}

Note:

  As extra match search implies additional modulefile evaluations, it
  is advised to build and use Module cache to improve search speed.

Two new elements, "variant" and "variantifspec", are added to the
allowed value list of "avail_output" and "avail_terse_output"
configuration options. The latter is set in the default value list of
both options. When "variant" is set, variants and their possible
values are reported along module they are associated to. When
"variantifspec" is set, available variants are reported only if a
variant is specified in search query.

   $ module config --reset avail_output
   $ module config avail_output
   Modules Release 5.3.0 (2023-05-14)

   - Config. name ---------.- Value (set by if default overridden) ---------------
   avail_output              modulepath:alias:dirwsym:sym:tag:variantifspec:key
   $ module avail foo
   --------------------- /path/to/modulefiles ---------------------
   foo/1.0  foo/2.0

   Key:
   modulepath
   $ module avail foo %a
   --------------------- /path/to/modulefiles ---------------------
   foo/1.0{%a}  foo/2.0{%a,b,c}

   Key:
   modulepath       {%value}={toolchain=value}
   default-version  {variant=value}


Extra specifiers
----------------

Extra specifiers are introduced to query content of modulefiles. They
can be specified with *element:name* syntax as part of module
specification on module search commands ("avail", "paths" and and
"whatis").

Extra specifiers trigger Extra match search mechanism when found in
module specification. Available modulefiles are evaluated in *scan*
mode to collect the different Tcl modulefile commands they use.

   $ module avail variant:toolchain
   --------------------- /path/to/modulefiles ---------------------
   bar/1.0  bar/2.0  foo/1.0  foo/2.0  qux/1.0  qux/2.0

In the above example, all modulefiles defining a "toolchain" variant
are returned.

Most Tcl modulefile commands can be queried with extra specifiers:
"variant", "setenv", "unsetenv", "append-path", "prepend-path",
"remove-path", "pushenv", "complete", "uncomplete", "set-alias",
"unset-alias", "set-function", "unset-function", "chdir", "family",
"prereq", "prereq-any", "prereq-all", "depends-on", "always-load",
"load", "load-any", "try-load", "switch", "switch-on", "switch-off",
"conflict" and "unload". Commands that handle environment variables
may be aliased "envvar". Commands that define a module requirement may
be aliased "require" and those that define a module incompatibility
may be aliased "incompat".

When several extra specifiers are set in query, modules returned are
those matching both conditions. In the following example, all
modulefiles interacting with "PATH" environment variable and requiring
"foo" module are returned.

   $ module avail envvar:PATH require:foo
   --------------------- /path/to/modulefiles ---------------------
   bar/1.0  bar/2.0

Extra specifiers related to module requirement or incompatibility may
leverage the Advanced module version specifiers syntax. On following
example, modulefiles returned are those defining a requirement on
"foo" module with version higher or equal to "1.2" and variant
"toolchain=a" selected.

   $ module avail "require:foo@1.2: toolchain=a"
   --------------------- /path/to/modulefiles ---------------------
   bar/1.0

Note:

  Module aliases or symbolic versions used either in modulefile
  definitions or as extra specifier values are not resolved.


Append or subtract elements to current option value
---------------------------------------------------

For command-line switches and configuration options whose value is a
colon-separated list, it is now possible to append or subtract
elements to the current value. With a "+" prefix elements are appended
and with a "-" prefix elements are subtracted.

This new feature applies to "--output"/"-o" command-line switches and
"avail_output", "avail_terse_output", "list_output",
"list_terse_output", "colors", "protected_envvars",
"shells_with_ksh_fpath", "tag_abbrev", "tag_color_name",
"variant_shortcut" configuration options.

For instance, to output available *foo* modules without modulepath and
tag information:

   $ module -o -modulepath:tag avail foo
   foo/1.0  foo/2.0

On following example, terse output mode of *list* sub-command is
permanently updated to report variant information:

   $ module config list_terse_output
   Modules Release 5.3.0 (2023-05-14)

   - Config. name ---------.- Value (set by if default overridden) ---------------
   list_terse_output         header
   $ module config list_terse_output +variant
   $ module config list_terse_output
   Modules Release 5.3.0 (2023-05-14)

   - Config. name ---------.- Value (set by if default overridden) ---------------
   list_terse_output         header:variant (env-var)


v5.2
====

This new version is backward-compatible with previous version 5
release. It fixes bugs but also introduces new functionalities that
are described in this section. See the 5.2 release notes for a
complete list of the changes between Modules v5.1 and v5.2.


Optional requirements
---------------------

The "--optional" option has been added to the "prereq", "prereq-all",
"depends-on" and "always-load" modulefile commands to indicate that
specified requirement is optional. An automatic load attempt is also
performed for optional requirements. If requirement is not found or
cannot be loaded, the dependency is yet considered satisfied as it is
optional.

   $ module show foo
   -------------------------------------------------------------------
   /path/to/modulefiles/foo:

   prereq          --optional bar
   -------------------------------------------------------------------
   $ module load foo
   Loading foo
     Loading requirement: bar

If the optional requirement is unloaded or loaded afterward, the
dependent module is automatically reloaded thanks to the
"auto_handling" mechanism.

   $ module unload bar
   Unloading bar
     Unloading dependent: foo
     Reloading dependent: foo
   $ module list
   Currently Loaded Modulefiles:
    1) foo
   $ module load bar
   Loading bar
     Unloading dependent: foo
     Reloading dependent: foo

Modules loaded by other modules with the "module try-load" command are
now considered optional requirements. Dependent module can be loaded
without the *try-load* modules, but now it gets automatically reloaded
if *try-load* module is loaded afterward, to take it into account.


Linting modulefiles
-------------------

Static analysis of modulefile, modulerc and global/user rc is now
possible with "lint" sub-command. It relies on an external program
defined with "tcl_linter" configuration option. Modules or files
specified on the command-line are resolved then passed to the Tcl
linter program.

   $ cat /path/to/modulefiles/foo/1.0
   #%Module
   if {"str" eq} {
    else {
   }
   $ module lint foo/1.0
   Linting /path/to/modulefiles/foo/1.0
     ERROR   line 2: Could not complete statement.
       One close brace would complete the first line
       One close brace would complete at end of line 4.
       One close brace would complete the script body at line 5.
       Assuming completeness for further processing.
     ERROR   line 2: Bad expression: missing operand at _@_
       in expression ""str" eq_@_"
     WARNING line 3: Unknown command "else"
     NOTICE  line 4: Close brace not aligned with line 3 (1 0)

Nagelfar is the Tcl linter recommended for Modules and set by default.
This default can be changed at installation time with "--with-tcl-
linter" and "--with-tcl-linter-opts" options. It can also be
configured later on through "tcl_linter" config option.

Specific syntax databases and plugins for Nagelfar are added by
Modules to precisely lint modulefile commands syntax in addition to
regular Tcl syntax. The installation of these specific files is
controlled with "--enable-nagelfar-addons" option (enabled by
default). Their location is controlled by the "--nagelfardatadir"
option.

   $ module lint bar@:1 /path/to/modulefiles/.modulerc
   Linting /path/to/modulefiles/.modulerc
     ERROR   line 35: Wrong number of arguments (3) to "module-alias"
     ERROR   line 41: Wrong number of arguments (3) to "module-virtual"

   Linting /path/to/modulefiles/bar/1.2
     WARNING line 19: Unknown command "unk"
   $ module lint ~/.modulerc
   Linting /home/user/.modulerc
     WARNING line 2: Command "setenv" should not be be used in global rc file

"lint" sub-command outputs messages returned by the Tcl linter
program. Nagelfar produces NOTICE, WARNING and ERROR messages. If
linter does not report a thing, "lint" sub-command will be silent,
unless if the "--verbose"/"-v" is set.

   $ module lint /path/to/modulefiles/bar/.version bar/1.4
   $ module lint -v /path/to/modulefiles/bar/.version bar/1.4
   Linting /path/to/modulefiles/bar/.version
   Linting /path/to/modulefiles/bar/1.4

When no file is specified to "lint" sub-command, all the global/user
rc files and all the modulefiles and modulercs from enabled
modulepaths are analyzed. If the "--all"/"-a" option is set, all
hidden modulefiles are also linted.

   $ module lint
   Linting /home/user/.modulerc
     WARNING line 2: Command "setenv" should not be be used in global rc file

   Linting /path/to/modulefiles/.modulerc
     ERROR   line 35: Wrong number of arguments (3) to "module-alias"
     ERROR   line 41: Wrong number of arguments (3) to "module-virtual"

   Linting /path/to/modulefiles/bar/1.2
     WARNING line 19: Unknown command "unk"
   ...

To use Nagelfar as Tcl linter for Modules, this open source tool has
to be installed on your system. When installing from tarball
distribution, make sure **nagelfar.tcl** command is found through a
"PATH" lookup or that "tcl_linter" option is set to its full path
location. Nagelfar is also made available as a RPM package in EPEL and
Fedora repositories.


mod-to-sh sub-command
---------------------

New sub-command is added to translate modulefile into shell code:
"mod-to-sh". It evaluates modulefiles passed as argument and produces
code for specified shell.

   $ cat /path/to/modulefiles/foo
   #%Module
   setenv FOO value
   set-function foo {echo foo}
   $ module mod-to-sh bash foo
   FOO=value; export FOO;
   foo () { echo foo; }; export -f foo;

Designated modulefiles are evaluated as if they were loading. But
instead of producing shell code that is evaluated in current shell
session, **module** command outputs this shell code.

   $ cat /path/to/modulefiles/bar
   #%Module
   setenv BAR othervalue
   set-alias bar {echo bar}
   $ module mod-to-sh fish foo bar
   set -xg FOO value;
   set -xg BAR othervalue;
   alias bar echobar;
   function foo; echo foo; end;
   $ module list
   No Modulefiles Currently Loaded.

All shells supported by "modulecmd.tcl" script are supported by "mod-
to-sh".

   $ module mod-to-sh python foo bar
   import os
   os.environ['FOO'] = 'value'
   os.environ['BAR'] = 'othervalue'


Initial environment
-------------------

When Modules initializes, it evaluates the "initrc" and "modulespath"
configuration files to enable default modulepaths and load default
modules. Initial environment corresponds to the environment state
after this initialization.

Initial environment is now saved in an environment variable
("__MODULES_LMINIT") in current shell session to remember what are the
initial modulepaths and initial modules with their tags and variants
if any.

"reset" sub-command is introduced, in a similar fashion than on Lmod,
to restore the initial environment. Here, "reset" relies on the
collection mechanism based and the content of "__MODULES_LMINIT".
Currently enabled modulepaths and loaded modules are respectively
unused and unloaded to use the modulepaths and load the modules with
tags and variants as described by initial environment.

   $ module list
   Currently Loaded Modulefiles:
    1) foo/1.0   2) bar/1.0
   $ module switch bar/1.0 qux/1.0
   $ module reset
   Unloading qux/1.0
   Loading bar/1.0

"restore" sub-command has been adapted to reinitialize the environment
to its initial state when no collection name is provided and no
*default* collection exists or if "__init__" virtual collection name
is provided.

It is possible to view the content of the initial environment with
"saveshow" sub-command. It is displayed when no argument is provided
and no collection exists or if "__init__" name is provided.

   $ module saveshow __init__
   -------------------------------------------------------------------
   initial environment:

   module use --append /path/to/modulefiles
   module load foo/1.0
   module load bar/1.0

   -------------------------------------------------------------------

Users have the ability to define what is their initial environment
state and thus adapt the behavior of "reset" sub-command with
"reset_target_state" configuration option. Default value is "__init__"
and it corresponds to the behavior described above. When set to
"__purge__", a "purge" command is performed when resetting. Any other
value corresponds to the name of a collection to restore.

   $ module config reset_target_state __purge__
   $ module reset
   Unloading bar/1.0
   Unloading foo/1.0


Stashing environment
--------------------

The ability to stash current environment is added with the
introduction of the "stash" sub-command. When called current
environment is saved in a *stash* collection then initial environment
is restored.

   $ module list
   Currently Loaded Modulefiles:
    1) bar/2.0   2) foo/2.0
   $ module stash
   Unloading foo/2.0
   Unloading bar/2.0
   $ module list
   No Modulefiles Currently Loaded.

Sub-commands are added to specifically handle stash collections. Their
names are prefixed with *stash*, like "stashlist" to list existing
stash collections or "stashshow" to display their content.

   $ module stashlist
   Stash collection list:
    0) stash-1665377597432   1) stash-1664946764252
   $ module stashshow
   -------------------------------------------------------------------
   /home/user/.module/stash-1665377597432:

   module use --append /path/to/modulefiles
   module load bar
   module load foo

   -------------------------------------------------------------------

Stash collections can be designated on sub-commands by their
collection name or stash index. Most recent stash collection has index
"0", the one after is designated with index "1", and so on. When no
stash collection is specified, most recent one is assumed.

   $ module stashshow 1
   -------------------------------------------------------------------
   /home/user/.module/stash-1664946764252:

   module use --append /path/to/modulefiles
   module load foobar

   -------------------------------------------------------------------

Stash collections are restored with the "stashpop" sub-command. It
changes the user environment to match the stash definition, then it
deletes the stash collection file.

   $ module stashpop
   Loading bar/2.0
   Loading foo/2.0
   $ module stashlist
   Stash collection list:
    0) stash-1664946764252

Stash collections can be deleted one by one with "stashrm" sub-command
or all together with "stashclear".

   $ module stashrm
   $ module stashlist
   No stash collection.


Siteconfig hook variables
-------------------------

Several Tcl variables are introduced for Site-specific configuration
script to define specific commands and variables in the evaluation
context of modulefiles and modulercs. These commands and variables
setup in "siteconfig.tcl" can be used in modulefile or modulerc. Sites
can easily extend modulefile and modulerc syntax with specific
elements.

"modulefile_extra_cmds" variable defines a list of commands to expose
in the modulefile evaluation context and the associated procedure to
run when this command is called. This variable has to be defined in
"siteconfig.tcl" located for instance at "/etc/environment-
modules/siteconfig.tcl".

In the following example "modulefile_extra_cmds" is used to define the
"sys" command and bound it to the "sys" procedure that is also defined
in "siteconfig.tcl".

   proc sys {mode} {
      switch -- $mode {
         name    { return myhost-$::tcl_platform(machine) }
         default { error "Unknown mode '$mode'" }
      }
   }
   set modulefile_extra_cmds {sys sys}

Once "siteconfig.tcl" is setup, the "sys" command can be called by
modulefiles. In the following example it is used to determine the
application path.

   $ cat /path/to/modulefiles/foo/1.2
   #%Module
   append-path PATH /path/to/apps/foo-1.2/[sys name]/bin

   $ module show foo/1.2
   -------------------------------------------------------------------
   /path/to/modulefiles/foo/1.2:

   append-path     PATH /path/to/apps/foo-1.2/myhost-x86_64/bin
   -------------------------------------------------------------------

"modulerc_extra_cmds" follows the same approach than
"modulefile_extra_cmds" and makes specific commands available during
modulerc evaluation.

"modulefile_extra_vars" variable defines a list of variables to expose
in the modulefile evaluation context and their associated value. This
variable has to be defined in "siteconfig.tcl".

In the following example "modulefile_extra_vars" is used to define the
"APP_ROOT" variable with "/path/to/apps" as value.

   set modulefile_extra_vars {APP_ROOT /path/to/apps}

Once "siteconfig.tcl" is setup, the "APP_ROOT" variable can be used in
modulefiles.

   $ cat /path/to/modulefiles/bar/2.1
   #%Module
   append-path PATH $APP_ROOT/bar-2.1/[sys name]/bin

   $ module show bar/2.1
   -------------------------------------------------------------------
   /path/to/modulefiles/bar/2.1:

   append-path     PATH /path/to/apps/bar-2.1/myhost-x86_64/bin
   -------------------------------------------------------------------

"modulerc_extra_vars" follows the same approach than
"modulefile_extra_vars" and makes specific variables available during
modulerc evaluation.


v5.1
====

This new version is backward-compatible with previous version 5
release. It fixes bugs but also introduces new functionalities that
are described in this section. See the 5.1 release notes for a
complete list of the changes between Modules v5.0 and v5.1.


Control output redirection
--------------------------

Since version 4.0, the **module** function is initialized differently
on *sh*, *bash*, *ksh*, *zsh* and *fish* shells when their session is
found interactive. In such situation **module** redirects its output
from *stderr* to *stdout*. Once initialized the redirection behavior
is inherited in sub-sessions.

The "redirect_output" configuration option is introduced in version
5.1, to supersede the default behavior set at initialization time.

   $ module load unknown >/dev/null
   $ module config redirect_output 0
   $ module load unknown >/dev/null
   ERROR: Unable to locate a modulefile for 'unknown'

The "--redirect" and "--no-redirect" command-line switches are also
added to change the output redirection behavior for a single command:

   $ module load unknown --redirect >/dev/null
   $ module load unknown --no-redirect >/dev/null
   ERROR: Unable to locate a modulefile for 'unknown'


Change modulefile command behavior
----------------------------------

Depending on the evaluation mode of the modulefile (e.g. *load*,
*unload*, *display*, etc) commands have different behavior. Most
common example is the "setenv" command that sets an environment
variable when modulefile is loaded and unsets it when it is unloaded.
A different behavior may be wished sometimes for commands. This is why
options are introduced for some modulefile commands to control what
happens on particular evaluation mode.

The "--return-value" option is added to the "getenv" and "getvariant"
modulefile commands to ensure that the value of the designated
environment variable or variant is returned even if modulefile is
evaluated in *display* mode:

   $ cat /path/to/modulefiles/foo/1.0
   #%Module5.1
   if {[getenv --return-value VAR] eq {}} {
       setenv VAR value
   }
   $ module display foo/1.0
   -------------------------------------------------------------------
   /path/to/modulefiles/foo/1.0:

   setenv          VAR value
   -------------------------------------------------------------------

"--remove-on-unload", "--append-on-unload", "--prepend-on-unload" and
"--noop-on-unload" options are added to the "remove-path" and "module
unuse" modulefile commands to control the behavior applied when
modulefile is unloaded. With these options it is possible for instance
to restore the paths unset at load time or to set other paths:

   $ module display bar/1.0
   -------------------------------------------------------------------
   /path/to/modulefiles/bar/1.0:

   module          unuse --prepend-on-unload /path/to/dir1
   module          use /path/to/dir2
   -------------------------------------------------------------------
   $ module use
   Search path for module files (in search order):
     /path/to/dir1
     /path/to/modulefiles
   $ module bar/1.0
   $ module use
   Search path for module files (in search order):
     /path/to/dir2
     /path/to/modulefiles
   $ module unload bar/1.0
   $ module use
   Search path for module files (in search order):
     /path/to/dir1
     /path/to/modulefiles

Following the same trend, the "--unset-on-unload" and "--noop-on-
unload" options are added to the "unsetenv" modulefile command to be
able to choose between unsetting variable, setting a value or
performing no operation when modulefile is unloaded.


Reducing number of I/O operations
---------------------------------

A new configuration option named "mcookie_check" is introduced to
control the verification made to files to determine if they are
modulefiles. By default this configuration option is set to "always"
and when searching for modulefiles within enabled modulepaths each
file below these directories is opened to check if it starts with the
Modules magic cookie (i.e., "#%Module" file signature).

These historical checks lead to a large number of I/O operations on
large module setup like in the below example where a total of 1098
modulefiles are available:

      $ module -o "" avail -t | wc -l
      1098
      $ module config mcookie_check always
      $ strace -f -e open,openat,read,close -c $MODULES_CMD bash avail
      ...
      % time     seconds  usecs/call     calls    errors syscall
      ------ ----------- ----------- --------- --------- ----------------
       44.29    0.044603          25      1734       166 open
       34.15    0.034389          16      2056           close
       11.87    0.011949          24       483         5 openat
        9.69    0.009761           4      2146           read
      ------ ----------- ----------- --------- --------- ----------------
      100.00    0.100702                  6419       171 total

For each file, 3 I/O operations ("open", "read" and "close") are
achieved to determine if it is a modulefile and include it in search
results. When modulefiles are located in a shared filesystem
concurrently accessed by hundreds of users, a "module avail" command
may take some time to finish.

When setting the "mcookie_check" configuration option to the "eval"
value, files are not checked anymore when searching for modulefiles,
only when evaluating them. All files under modulepaths are considered
modulefiles, so the content of these directories must be carefully
checked to use this "mcookie_check" mode which lead to a significant
reduction of I/O operations:

      $ module config mcookie_check eval
      $ strace -f -e open,openat,read,close -c $MODULES_CMD bash avail
      ...
      % time     seconds  usecs/call     calls    errors syscall
      ------ ----------- ----------- --------- --------- ----------------
       30.56    0.013717          14       944           close
       28.76    0.012911          21       612       156 open
       26.41    0.011857          24       483         5 openat
       14.26    0.006403           6      1034           read
      ------ ----------- ----------- --------- --------- ----------------
      100.00    0.044888                  3073       161 total

A substantial reduction of execution time may be noticed depending on
the storage setup used to host the modulepath directories. A special
care should be given to the content of these directories to ensure
they only contain modulefiles (see "MODULES_MCOOKIE_CHECK").

See the Reduce I/O load cookbook recipe to learn additional features
of Modules that could be leveraged to lower the number of I/O
operations.


Shell command completion
------------------------

New modulefile commands "complete" and "uncomplete" are added to get
the ability to respectively define and unset command completion.
*bash*, *tcsh* and *fish* shells are supported.

   > module display foo
   -------------------------------------------------------------------
   /path/to/modulefiles/foo/1.0:

   append-path     PATH /path/to/foo-1.0/bin
   complete        fish foo {-s V -l version --description 'Command version'}
   complete        fish foo {-s h -l help --description 'Command help'}
   -------------------------------------------------------------------
   > module load foo
   > foo -<TAB>
   -h  --help  (Command help)  -V  --version  (Command version)

"sh-to-mod" sub-command and "source-sh" modulefile command have also
been updated to track shell completion changes.

   $ module sh-to-mod bash /path/to/foo-1.0/share/setup-env.sh
   #%Module
   complete        bash foo {-o default -F _foo}
   append-path     PATH /path/to/foo-1.0/bin
   set-function    _foo {
       ...bash completion code...}


Lmod Tcl modulefile support
---------------------------

With this new version, Modules now supports Tcl modulefiles written
for Lmod, the alternative **module** implementation developed in Lua.
Such modulefiles can be safely evaluated by Modules without raising
error.

Support has been added for the following modulefile commands
introduced by Lmod: "depends-on", "prereq-any", "always-load", "module
load-any", "pushenv", "require-fullname" and "family".

The Compatibility with Lmod Tcl modulefile section in the modulefile
man page describes the differences existing between the two
implementations.

Note that when processing a "family" command, the "LMOD_FAMILY_<NAME>"
environment variable is defined by Modules to be compatible with
existing modulefiles or scripts relying on such variable.


More tagging capabilities
-------------------------

The new "--tag" option helps to define extra tags onto a loading
module. These tags comes in addition to those inherited from the
module state or those associated with the "module-tag" modulefile
command.

The "--tag" option is available on "load", "load-any", "switch" and
"try-load" sub-commands and on "always-load", "depends-on", "module",
"prereq", "prereq-all" and "prereq-any" modulefile commands.

Informational messages of module evaluation have been updated to
mention in module denomination the tags applying to it, as it is done
in "list" sub-command output:

   $ module load -v --tag=sticky:bar foo/1.0
   Loading foo/1.0 <bar>

In case the designated module is already loaded, the additional tags
are added to the list of tags already applied to this module.

   $ module list
   Currently Loaded Modulefiles:
    1) foo/1.0
   $ module load -v --tag=sticky:bar foo/1.0
   Tagging foo/1.0 <bar>

The "keep-loaded" tag is introduced in this version. It avoids an
auto-loaded module to get automatically unloaded when its dependent
modules are unloaded. This new tag can be set with the "module-tag"
modulefile command or when module is loaded with the "always-load"
modulefile command. Default "tag_abbrev" configuration option has been
updated to add the "kL" abbreviation for "keep-loaded" tag. Default
dark and light color palettes have been updated too.

   $ module show bar/1.0
   -------------------------------------------------------------------
   /path/to/modulefiles/bar/1.0:

   always-load     foo/1.0
   -------------------------------------------------------------------
   $ module load bar/1.0
   Loading bar/1.0
     Loading requirement: foo/1.0
   $ module unload bar/1.0
   $ module list
   Currently Loaded Modulefiles:
    1) foo/1.0

   Key:
   auto-loaded  keep-loaded

When saving a collection, the tags defined with "--tag" option are
recorded to set them again when collection is restored. Tags resulting
from module load state, like "auto-loaded" and "keep-loaded", are also
recorded.

   $ module load --tag=sticky bar/1.0
   Loading bar/1.0
     Loading requirement: foo/1.0
   $ module save
   $ module saveshow
   -------------------------------------------------------------------
   /home/user/.module/default:

   module use --append /path/to/modulefiles
   module load --tag=auto-loaded:keep-loaded foo
   module load --tag=sticky bar

   -------------------------------------------------------------------

The "collection_pin_tag" configuration option is added to record in
collection all tags set on loaded modules. This configuration option
is disabled by default.

Note:

  Collection saved now starts with a "#%Module5.1" file signature if "
  --tag" option is recorded in it. Such collection could only be
  handled by Modules version 5.1 and above.


v5.0
====

With this new major version the **module** experience has been updated
to benefit by default from all the advanced behaviors and features
developed over the Modules 4 versions. Modules 5.0 also introduces
some breaking changes to improve the consistency of the whole
solution. See the 5.0 release notes for a complete list of the changes
between Modules v4.8 and v5.0. The changes document gives an in-depth
view of the modified behaviors.


Upgraded default configuration
------------------------------

Release after release, new advanced features were added on Modules 4.
They were set off by default to avoid breaking change during the
version 4 cycle. With the move to a new major release, these features
are set on to improve by default usages for everybody. These features
enabled by default are:

* Automated module handling mode which provides the automatic
  dependency resolution when loading and unloading modules

     $ module load foo/1.0
     Loading foo/1.0
       Loading requirement: bar/1.0

* Extended default that enables to select a module when the first
  number in its version is specified

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

* Advanced module version specifiers, an improved syntax to designate
  module version in range or list and module variant

     $ module load foo@:2.2 %gcc11
     Loading foo/2.1{%gcc11}
       Loading requirement: bar/1.2{-debug:%gcc11}

* Colored output to graphically enhance parts of the produced output
  to improve readability

     $ ml av
     ------------------ /path/to/modulefiles ------------------
     bar/1.0  bar/2.0  foo/1.0  foo/2.0  foo/2.2

     Key:
     modulepath       module-alias  sticky
     default-version  forbidden

* Specify modules in a case insensitive manner search that matches
  modules using a different character case than the one expressed in
  search query

     $ ml av liba
     ------------------ /path/to/modulefiles ------------------
     LibA/1.0  LibA/2.0

Some other features that were enabled by default during the Modules 4
cycle have been turned off as they may not be useful for basic usages.
Among other things setting off the following features makes the
definition of the **module** function simpler. Even if off by default,
these features can now be enabled once Modules is installed through
the "initrc" configuration file.

* *Set shell startup* files to ensure the **module** command is
  defined once shell has been initialized. See the "set_shell_startup"
  configuration option to activate.

* *Quarantine mechanism* that protects the **module** command run-time
  environment from side effect coming from the current environment
  definition. See the "quarantine_support" configuration option to
  activate.

* *Silent shell debug* which disables the debugging property set on
  current shell session for the duration of the **module** command.
  See the "silent_shell_debug" configuration option to activate.


Removing compatibility version
------------------------------

The ability to co-install version 3.2 of Modules along newer version
is discontinued. The installation option "--enable-compat-version",
**switchml** shell function and "MODULES_USE_COMPAT_VERSION"
environment variables are thus removed.

The interesting features of Modules 3.2 that were missing in the
initial Modules 4 release in 2017 have been reintroduced progressively
(like "clear" sub-command or "--icase" search). With Modules 5.0, the
"refresh" sub-command is even changed to the behavior it had on
Modules 3.2. So it is a good time for the big jump.

If you are still using Modules 3.2, please refer to the Changes
between versions document that describes the differences of this
version compared to the newer releases.


Improving Modules initialization
--------------------------------

Modules initialization files are now installed by default in the *etc*
directory designated by the "--etcdir" installation option. The
initialization configuration file is named "initrc" in this directory,
and the  modulepath-specific configuration file is named
"modulespath". When both files exist, now they are both evaluated
instead of just the "modulespath" file.

Modules magic cookie (i.e., "#%Module" file signature) is now required
at the start of "initrc". An error is produced if the magic cookie is
missing or if the optional version number placed after the cookie
string is higher than the version of the "modulecmd.tcl" script in
use.

Note that "initrc" configuration file can host more than "module use"
and "module load" commands. **module** configuration can also be
achieved with this file through the use of "module config" commands.

Modules initialization has been enhanced for situations where a module
environment is found already defined. In this case the loaded modules
are automatically refreshed which is useful to re-apply the non-
persistent environment configuration (i.e., shell alias and function
that are not exported to the sub-shell). For instance when starting a
sub-shell session it ensures that the loaded environment is fully
inherited from parent shell:

   $ ml show foo/1.0
   -------------------------------------------------------------------
   /path/to/modulefiles/foo/1.0:

   set-alias       foo {echo foo}
   -------------------------------------------------------------------
   $ ml foo/1.0
   $ alias foo
   alias foo='echo foo'
   $ bash
   $ ml
   Currently Loaded Modulefiles:
    1) foo/1.0
   $ alias foo
   alias foo='echo foo'


Simplifying path-like variable reference counting
-------------------------------------------------

The reference counting mechanism used for path-like environment
variable enables to determine if a path entry has been added several
times (by several loaded modules for instance) to know whether or not
this path entry should be unset when unloading a module. Entry is not
removed if multiple loaded modules rely on it.

The mechanism is not applied anymore to the Modules-specific path
variables (like "LOADEDMODULES") as an element entry in these
variables cannot be added multiple times without duplication. For
instance, a given module name and version cannot be added twice in
"LOADEDMODULES" as this module is only loaded once. With this change a
thinner environment is produced by **module**. An exception is made
for "MODULEPATH" environment variable where the mechanism still
applies.

   $ $MODULES_CMD bash load foo/2.0
   _LMFILES_=/path/to/modulefiles/foo/2.0; export _LMFILES_;
   LOADEDMODULES=foo/2.0; export LOADEDMODULES;
   __MODULES_LMTAG=foo/2.0&mytag; export __MODULES_LMTAG;
   test 0;

Reference counting mechanism has also been simplified for entries in
path-like variable that are only referred once. For such entries no
entry is set in the reference counting variable (which are now called
"__MODULES_SHARE_<VAR>"). A reference count entry is set only if the
entry in the path-like variable is referred more than one time.

   $ ml foo/3.0
   $ echo $PATHVAR
   /path/to/dir1
   $ echo $__MODULES_SHARE_PATHVAR

   $ ml bar/1.0
   $ echo $PATHVAR
   /path/to/dir1
   $ echo $__MODULES_SHARE_PATHVAR
   /path/to/dir1:2
   $ ml -foo/3.0
   $ echo $PATHVAR
   /path/to/dir1
   $ echo $__MODULES_SHARE_PATHVAR

   $

When the "use" and "unuse" module sub-commands are not called during a
modulefile evaluation, the reference counter associated with each
entry in "MODULEPATH" environment variable is ignored. In such
context, a "module use" will not increase the reference counter of a
path entry already defined and a "module unuse" will remove specified
path whatever its reference counter value. Same change applies for
"append-path", "prepend-path" and "remove-path" module sub-commands
when called from the command-line.

   $ echo $MODULEPATH
   /path/to/modulefiles
   $ echo $__MODULES_SHARE_MODULEPATH
   /path/to/modulefiles:2
   $ ml use /path/to/modulefiles
   $ echo $__MODULES_SHARE_MODULEPATH
   /path/to/modulefiles:2
   $ ml unuse /path/to/modulefiles
   $ echo $MODULEPATH

   $ echo $__MODULES_SHARE_MODULEPATH

   $


v4.8
====

This new version is backward-compatible with previous version 4
releases. It fixes bugs but also introduces new functionalities that
are described in this section. See the 4.8 release notes for a
complete list of the changes between Modules v4.7 and v4.8.


Editing modulefiles
-------------------

"edit" sub-command is introduced to give the ability to open
modulefiles in a text editor. Modulefiles can be specified like with
any other sub-command: using regular, symbolic or aliased names or
using advanced version specifiers.

   $ ml edit foo

"edit" sub-command resolves the path toward the designated modulefile
then call configured text editor to open this modulefile with it.
Below, the modulefile is opened with the "vi" command:

   #%Module
   module-whatis [module-info name]
   setenv PATH /path/to/foo-1.0/bin
   ~
   ~
   ~
   "/path/to/modulefiles/foo/1.0" 3L, 42B 1,1           All

The "editor" configuration option controls the editor command to use.
This option can be configured at installation time with the "--with-
editor" installation option. If not set, "editor" configuration option
is set by default to "vi".

"editor" configuration option can be changed with the "config" sub-
command. Which sets the "MODULES_EDITOR" environment variable.

The "VISUAL" or the "EDITOR" environment variables override the
default value of "editor" configuration option but are overridden by
the "MODULES_EDITOR" environment variable.


Using version range in version list
-----------------------------------

The Advanced module version specifiers mechanism has been improved to
allow the use of version range (*@:version*, *@vers1:vers2* or
*@version:*) within version list (*@version1,version2,...*).

It is now possible to write for instance "mod@:1.2,1.4:1.6,1.8:" to
designate all versions of module *mod*, except versions *1.3* and
*1.7*.

This improvement is available where the advanced version specifier
syntax is supported. Thus it can be either used from the command-line
or when writing modulefiles, for instance to hide or tag modules or to
declare requirements.


Try module load with no complain if not found
---------------------------------------------

Add the "try-load" sub-command that tries to load the modulefile
passed as argument, like the "load" sub-command, but does not raise an
error if this modulefile cannot be found.

   $ module load unknown
   ERROR: Unable to locate a modulefile for 'unknown'
   $ echo $?
   1
   $ module try-load unknown
   $ echo $?
   0
   $ module list
   No Modulefiles Currently Loaded.

This sub-command first introduced by the Lmod project is added to
Modules to improve the compatibility between the two "module"
implementations.

"try-load" is also available within modulefile context to continue the
evaluation of a modulefile in case no module is found in its attempt
to load another modulefile

   $ module display foo/1.0
   -------------------------------------------------------------------
   /path/to/modulefiles/foo/1.0:

   module   try-load unknown/1.0
   -------------------------------------------------------------------
   $ module load foo/1.0
   $ module list
   Currently Loaded Modulefiles:
    1) foo/1.0


Module variants
---------------

Module variants is a new mechanism that allows to pass arguments to
evaluated modulefiles in order to achieve different environment
variable or module requirement setup with a single modulefile.

Variant specification relies on the Advanced module version specifiers
mechanism, which leverages the variant syntax of the Spack package
manager:

   $ module config advanced_version_spec 1
   $ module load -v bar/1.2 toolchain=a -debug
   Loading bar/1.2{-debug:toolchain=a}

Variants are defined in modulefile with the "variant" command, which
defines the variant type and its accepted values:

   #%Module4.8
   variant toolchain a b c
   variant --boolean --default off debug

   # select software build depending on variant values
   set suffix -[getvariant toolchain]
   if {$ModuleVariant(debug)} {
       append suffix -dbg
   }

   prepend-path PATH /path/to/bar-1.2$suffix/bin
   prepend-path LD_LIBRARY_PATH /path/to/bar-1.2$suffix/lib

The *bar/1.2* modulefile defines a "toolchain" variant, which accepts
the "a", "b" and "c" values, and a "debug" Boolean variant, which is
set "off" by default. Once these two variants are declared, their
value specified on module designation are instantiated in the
"ModuleVariant" array variable which could also be queried with the
"getvariant" modulefile command. Selected variant values enable to
define a specific installation build path for the *bar/1.2* software.

If a variant is not specified when designating module and if this
variant is not declared with a default value, an error is obtained:

   $ module purge
   $ module load bar@1.2
   Loading bar/1.2
     ERROR: No value specified for variant 'toolchain'
       Allowed values are: a b c

Once module is loaded, selected variants are reported on the "list"
sub-command output:

   $ module load bar@1.2 toolchain=b
   $ module list
   Currently Loaded Modulefiles:
    1) bar/1.2{-debug:toolchain=b}

   Key:
   {-variant}={variant=off}  {variant=value}

Note:

  The default value of the "--with-list-output" installation option
  has been updated to include variant information.

Variant specification could be used where the Advanced module version
specifiers is supported. For instance a module may express a
dependency over a specific module variant:

   $ module show foo/2.1 toolchain=c
   -------------------------------------------------------------------
   /path/to/modulefiles/foo/2.1:

   variant         toolchain a b c
   prereq          bar@1.2 toolchain={toolchain}
   prepend-path    PATH /path/to/foo-2.1-{toolchain}/bin
   prepend-path    LD_LIBRARY_PATH /path/to/foo-2.1-{toolchain}/lib
   -------------------------------------------------------------------

In this example, *foo/2.1* module depends on *bar/1.2* and the same
toolchain variant should be selected for both modules in order to load
two software builds that are compatible between each other.

   $ module purge
   $ module config auto_handling 1
   $ module load foo/2.1 toolchain=a
   Loading foo/2.1{toolchain=a}
     Loading requirement: bar/1.2{-debug:toolchain=a}


Variant shortcuts
-----------------

The "variant_shortcut" configuration option is added to define
shortcut characters for easily specifying variants. Instead of writing
the variant name to specify it in module designation (e.g.,
*name=value*), the shortcut associated to this variant could be used
(i.e., *<shortcut>value*):

   $ module purge
   $ module config variant_shortcut toolchain=%
   $ module load foo/2.1 %a
   Loading foo/2.1{%a}
     Loading requirement: bar/1.2{-debug:%a}

Configured shortcuts are also used to report the loaded variant on
"list" sub-command output (shortcuts are explained in key section):

   $ module list
   Currently Loaded Modulefiles:
    1) bar/1.2{-debug:%a}  2) foo/2.1{%a}

   Key:
   auto-loaded  {-variant}={variant=off}  {%value}={toolchain=value}  {variant=value}


v4.7
====

This new version is backward-compatible with previous version 4
releases. It fixes bugs but also introduces new functionalities that
are described in this section. See the 4.7 release notes for a
complete list of the changes between Modules v4.6 and v4.7.


Determining module implementation and version
---------------------------------------------

New Modules variables are introduced to determine during the
evaluation of a modulefile or a modulerc what *module* implementation
is currently in use. The "ModuleTool" variable corresponds to the name
of the *module* implementation and is set to "Modules" for this
project. The "ModuleToolVersion" variable corresponds to the version
number of the implementation (e.g. "4.7.0").

With these new variables it is possible to precisely know what
*module* command is in use then adapt modulefile code to handle a
specific behavior or leverage a new feature.

The modulefile command "versioncmp" is also introduced to provide a
simple way to compare two version strings and return if first version
string is less than, equal to or greater than second one.

   if {[info exists ModuleTool] && $ModuleTool eq {Modules}
       && [versioncmp $ModuleToolVersion 4.7] >= 0} {
       # here some code specific for Modules 4.7 and later versions
   }

The "ModuleTool" and "ModuleToolVersion" variables and the
"versioncmp" modulefile command are supported by the Lmod project
starting version "8.4.8".


Symbolic version to designate module loaded version
---------------------------------------------------

When the Advanced module version specifiers is enabled, the "loaded"
symbolic version may be used to designate the currently loaded version
of specified module.

   $ ml display foo@loaded
   -------------------------------------------------------------------
   /path/to/modulefiles/foo/1.0:

   module-whatis   foo/1.0
   -------------------------------------------------------------------

If no version of specified module can be found loaded, an error is
returned.

   $ ml display foo@loaded
   ERROR: No loaded version found for 'foo' module


Module tags
-----------

Module tags are piece of information that can be associated to
individual modulefiles. Tags could be purely informational or may lead
to specific behaviors.

Module tags may be inherited from the module state set by a modulefile
command or consequence of a module action. Tags may also be associated
to modules by using the new "module-tag" modulefile command.

Module tags are reported along the module they are associated to on
"avail" and "list" sub-command results. Tags could be reported either:

* along the module name, all tags set within angle brackets, each tag
  separated from the others with a colon character (e.g., "foo/1.2
  <tag1:tag2>").

   $ cat /path/to/modulefiles/foo/.modulerc
   #%Module
   module-tag mytag foo
   module-tag othertag foo/1.0
   $ ml av
   --------------- /path/to/modulefiles ---------------
   foo/1.0 <mytag:othertag>  foo/2.0 <mytag>
   $ ml foo/1.0
   $ ml
   Currently Loaded Modulefiles:
    1) foo/1.0 <mytag:othertag>

* graphically rendered over the module name for each tag associated to
  a Select Graphic Rendition (SGR) code in the color palette (see
  "MODULES_COLORS")

   $ # set SGR code to report 'mytag' with blue background color
   $ ml config colors "hi=1:di=94:L=90;47:mytag=102"
   $ ml av
   --------------- /path/to/modulefiles ---------------
   foo/1.0 <othertag>  foo/2.0
   $ ml
   Currently Loaded Modulefiles:
    1) foo/1.0 <othertag>

The "tag_abbrev" configuration option is available to define
abbreviated strings for module tags and then use these abbreviations
instead of tag names when reporting tags on "avail" and "list" command
results.

   $ # add abbreviation for 'othertag' tag
   $ ml config tag_abbrev loaded=L:othertag=oT
   $ ml av
   --------------- /path/to/modulefiles ---------------
   foo/1.0 <oT>  foo/2.0
   $ ml
   Currently Loaded Modulefiles:
    1) foo/1.0 <oT>

When a SGR code is set for a tag in the color palette, this graphical
rendition is applied by default over the module name and the tag name
or its abbreviation is not displayed. If tag name or abbreviation is
added to the "tag_color_name" configuration option, graphical
rendering is applied to the tag name or abbreviation rather than over
the module name they are attached to.

   $ # add SGR code for 'oT' tag and set rendition over tag name
   $ ml config colors "hi=1:di=94:L=90;47:mytag=44:oT=41"
   $ ml config tag_color_name oT
   $ ml av
   --------------- /path/to/modulefiles ---------------
   foo/1.0 <oT>  foo/2.0
   $ ml
   Currently Loaded Modulefiles:
    1) foo/1.0 <oT>

Tags inherited from module state, consequence of a module action or
set by using "module-tag" but that have a special meaning currently
are:

+--------------------+---------------------------+-------------------------+---------+------------------------+
| Tag                | Description               | Set with                | Abbr.   | Color                  |
|====================|===========================|=========================|=========|========================|
| auto-loaded        | Module has been loaded    | Inherited               | aL      | mod/1.0                |
|                    | automatically             |                         |         |                        |
+--------------------+---------------------------+-------------------------+---------+------------------------+
| forbidden          | Module cannot be loaded   | Inherited from "module- | F       | mod/1.0                |
|                    |                           | forbid"                 |         |                        |
+--------------------+---------------------------+-------------------------+---------+------------------------+
| hidden             | Module is not visible on  | Inherited from "module- | H       | mod/1.0                |
|                    | "avail"                   | hide"                   |         |                        |
+--------------------+---------------------------+-------------------------+---------+------------------------+
| hidden-loaded      | See Hiding loaded modules | Inherited from "module- | H       | mod/1.0                |
|                    |                           | hide"                   |         |                        |
+--------------------+---------------------------+-------------------------+---------+------------------------+
| loaded             | Module is currently       | Inherited               | L       | mod/1.0                |
|                    | loaded                    |                         |         |                        |
+--------------------+---------------------------+-------------------------+---------+------------------------+
| nearly-forbidden   | Module will soon not be   | Inherited from "module- | nL      | mod/1.0                |
|                    | able to load anymore      | forbid"                 |         |                        |
+--------------------+---------------------------+-------------------------+---------+------------------------+
| sticky             | See Sticky modules        | "module-tag"            | S       | mod/1.0                |
+--------------------+---------------------------+-------------------------+---------+------------------------+
| super-sticky       | See Sticky modules        | "module-tag"            | sS      | mod/1.0                |
+--------------------+---------------------------+-------------------------+---------+------------------------+


Hiding loaded modules
---------------------

The "--hidden-loaded" option has been added to the "module-hide"
modulefile command and it indicates that designated hidden modules
remain hidden after being loaded.

   $ cat /path/to/modulefiles/foo/1.0
   #%Module
   module load bar
   $ cat /path/to/modulefiles/bar/.modulerc
   #%Module4.7
   module-hide --soft --hidden-loaded bar

In this example, *foo* depends on *bar* which is set soft hidden and
hidden once loaded. As a consequence, automated load of *bar* module
will not be reported and *bar/1.0* will not appear in loaded module
list by default:

   $ ml foo
   $ ml
   Currently Loaded Modulefiles:
    1) foo/1.0

However *bar/1.0* is loaded. Hidden loaded modules can be unveiled
with the "--all"/"-a" option set on the "list" sub-command. "hidden-
loaded" tag (abbreviated by default to "H" when colored output is
disabled) applies to such modules.

   $ ml -a
   Currently Loaded Modulefiles:
    1) bar/1.0   2) foo/1.0

To also get the informational messages about hidden loaded module
automated load or unload, the new verbosity level "verbose2" can be
used (with "-vv" option for instance):

   $ ml purge
   $ ml -vv foo
   Loading bar/1.0

   Loading foo/1.0
     Loading requirement: bar/1.0


Sticky modules
--------------

Module stickiness is introduced, in a similar fashion than on the Lmod
project, to allow to glue modules to the loaded environment. A sticky
module cannot be unloaded, unless if the unload action is forced or if
the module reloads after being unloaded.

A modulefile is declared *sticky* by applying it the "sticky" tag with
the "module-tag" modulefile command.

   $ cat /path/to/modulefiles/foo/.modulerc
   #%Module4.7
   module-tag sticky foo/1.0
   $ ml
   Currently Loaded Modulefiles:
    1) foo/1.0
   $ ml -foo
   Unloading foo/1.0
     ERROR: Unload of sticky module 'foo/1.0' skipped
   $ ml
   Currently Loaded Modulefiles:
    1) foo/1.0
   $ ml --force -foo
   Unloading foo/1.0
     WARNING: Unload of sticky module 'foo/1.0' forced
   $ ml
   No Modulefiles Currently Loaded.

Modulefile can also be defined "super-sticky" by applying the
corresponding module tag. *Super-sticky* module cannot be unloaded
even if the unload action is forced. It can only be unloaded if the
module reloads afterward.

   $ cat /path/to/modulefiles/bar/.modulerc
   #%Module4.7
   module-tag super-sticky bar/1.0
   $ ml
   Currently Loaded Modulefiles:
    1) bar/1.0
   $ ml purge
   Unloading bar/1.0
     ERROR: Unload of super-sticky module 'bar/1.0' skipped
   $ ml purge -f
   Unloading bar/1.0
     ERROR: Unload of super-sticky module 'bar/1.0' skipped
   $ ml
   Currently Loaded Modulefiles:
    1) bar/1.0

Modulefiles targeted by a "sticky" or a "super-sticky" tag are colored
on "avail" and "list" sub-command outputs to indicate such tag
applies. If colored output is disabled a tag abbreviation is reported
along module designation (respectively "S" and "sS").

In case the stickiness applies to the generic module name (and does
not target a specific module version or version-set), one version of
the sticky or super-sticky module can be swapped by another version of
this same module:

   $ cat /path/to/modulefiles/baz/.modulerc
   #%Module4.7
   module-tag sticky baz
   $ ml
   Currently Loaded Modulefiles:
    1) baz/2.0
   $ ml switch baz/1.0
   $ ml
   Currently Loaded Modulefiles:
    1) baz/1.0


Explaining avail/list output
----------------------------

A *Key* section is added at the end of the "avail" and "list" sub-
commands output to give hints on the meaning of the graphical
rendition applied to elements or what the elements set in parentheses
or chevrons along module name stand for.

   $ ml av
   ------------------ /path/to/modulefiles ------------------
   foo/1.0 <oT>  foo/2.0  foo/3.0

   Key:
   loaded      default-version  sticky        <oT>=othertag
   modulepath  module-alias     <module-tag>


Configuring avail/list output
-----------------------------

New configuration options are introduced to control what content to
output in addition to modules names on the regular and terse output
modes of the "avail" and "list" sub-commands.

These new configuration options named "avail_output",
"avail_terse_output", "list_output" and "list_terse_output" can be
updated using the "config" sub-command or set at installation time
respectively with the "--with-avail-output", "--with-avail-terse-
output", "--with-list-output" and "--with-list-terse-output" configure
options.

The four options accept a colon separated list of elements as value.
Accepted elements for the "avail"-related options are: "modulepath",
"alias", "dirwsym", "sym", "tag" and "key". Accepted elements for the
"list"-related options are: "header", "idx", "sym", "tag" and "key".

In the following example, default output configuration for the "avail"
sub-command is checked then module tags and key section are removed to
get a simpler output:

   $ ml config avail_output
   Modules Release 4.7.0 (2021-02-19)

   - Config. name ---------.- Value (set by if default overridden) ---------------
   avail_output              modulepath:alias:dirwsym:sym:tag:key
   $ ml av
   ------------------ /path/to/modulefiles ------------------
   bar/1.0  bar/2.0  foo/1.0  foo/2.0  foo/2.2

   Key:
   modulepath       module-alias  sticky
   default-version  forbidden
   $ ml config avail_output modulepath:alias:dirwsym:sym
   $ ml av
   ------------------ /path/to/modulefiles ------------------
   bar/1.0  bar/2.0  foo/1.0  foo/2.0  foo/2.2

The "--output"/"-o" switches are added to define a specific output
configuration for the duration of the associated command line. The
following example shows how to limit the content reported on a module
"list" to the loaded index and the symbolic versions in addition to
the module names:

   $ ml
   Currently Loaded Modulefiles:
    1) bar/1.0   2) foo/2.0

   Key:
   default-version  sticky
   $ ml -o idx:sym
    1) bar/1.0   2) foo/2.0

When the new configuration options command line switches are set to an
empty value, the module names are the sole information reported:

   $ ml -t -o ""
   bar/1.0
   foo/2.0

In case the "modulepath" element is withdrawn from the "avail" sub-
command output configuration, the available modules from all enabled
modulepaths are reported as a single list:

   $ ml av
   --------------- /path/to/other/modulefiles ---------------
   baz/1.0  baz/2.0

   ------------------ /path/to/modulefiles ------------------
   bar/1.0  bar/2.0  foo/1.0  foo/2.0  foo/2.2

   Key:
   modulepath       module-alias  sticky
   default-version  forbidden
   $ ml av --output=alias:tag
   bar/1.0  baz/1.0  foo/1.0  foo/2.2
   bar/2.0  baz/2.0  foo/2.0

Note:

  The "avail_report_dir_sym" and "avail_report_mfile_sym" locked
  configuration options have been removed. Their behaviors can now be
  obtained by respectively adding the "dirwsym" and "sym" elements to
  the "avail_output" or "avail_terse_output" configuration options.


v4.6
====

This new version is backward-compatible with previous version 4
releases. It fixes bugs but also introduces new functionalities that
are described in this section. See the 4.6 release notes for a
complete list of the changes between Modules v4.5 and v4.6.


sh-to-mod sub-command
---------------------

The "sh-to-mod" sub-command is added to output as a modulefile content
the environment changes done by the evaluation of a shell script
passed as argument. "sh-to-mod" is especially useful for software
providing a shell script for their enablement in shell session: it can
convert these scripts into modulefiles.

Say for instance, a *foo* software has been installed and it provides
a "foo-setup.sh" script to activate *foo* software in user
environment:

   $ cat /path/to/foo-1.2/foo-setup.sh
   #!/bin/sh
   export FOOENV="$1"
   export PATH=/path/to/foo-1.2/bin:$PATH
   alias foo='foobin -q -l'

Calling "module sh-to-mod" on this shell script outputs the
environment changes it performs as a modulefile content:

   $ module sh-to-mod sh /path/to/foo-1.2/foo-setup.sh arg1
   #%Module
   prepend-path    PATH /path/to/foo-1.2/bin
   set-alias       foo {foobin -q -l}
   setenv          FOOENV arg1

Changes on environment variables, shell aliases, shell functions and
current working directory are tracked. The following shells are
supported: *sh*, *dash*, *csh*, *tcsh*, *bash*, *ksh*, *ksh93*, *zsh*
and *fish*.

"sh-to-mod" acts as a full replacement for the standalone
**createmodule.sh** and **createmodule.py** scripts. However those two
scripts are currently still provided for compatibility purpose.


source-sh modulefile command
----------------------------

The "source-sh" modulefile command is introduced to source environment
changes done by the evaluation of a shell script passed as argument.
With newly introduced "sh-to-mod" sub-command resulting environment
changes done by script are output as modulefile commands. "source-sh"
applies those modulefile commands as if they were directly written in
loading modulefile.

"source-sh" is useful for software providing a shell script for their
enablement. If you want to enable such software with **module** yet
using shell script provided by software for this task, just write a
modulefile using "source-sh" command to call the shell script.

Keeping the same example used to describe "sh-to-mod" sub-command:
*foo* software provides a "foo-setup.sh" script for its activation.
Create a modulefile "foo/1.2" that calls this script:

   $ cat /path/to/modulefiles/foo/1.2
   #%Module4.6
   source-sh sh /path/to/foo-1.2/foo-setup.sh arg1

Displaying this modulefile indicates the environment changes done by
script:

   $ module display foo/1.2
   -------------------------------------------------------------------
   /path/to/modulefiles/foo/1.2:

   prepend-path    PATH /path/to/foo-1.2/bin
   set-alias       foo {foobin -q -l}
   setenv          FOOENV arg1
   -------------------------------------------------------------------

Loading the modulefile applies the environment changes seen above:

   $ module load -v foo/1.2
   Loading foo/1.2
   $ echo $FOOENV
   arg1
   $ alias foo
   alias foo='foobin -q -l'

Track of these changes is kept in user environment to be able to undo
them when modulefile is unloaded:

   $ module unload -v foo/1.2
   Unloading foo/1.2
   $ echo $FOOENV

   $ alias foo
   bash: alias: foo: not found

Changes on environment variables, shell aliases, shell functions and
current working directory are tracked. The following shells are
supported: *sh*, *dash*, *csh*, *tcsh*, *bash*, *ksh*, *ksh93*, *zsh*
and *fish*.


Querying user's name and groups membership
------------------------------------------

Two new sub-commands are introduced for the "module-info" modulefile
command: "username" and "usergroups". They respectively fetch the name
of the user currently running "modulecmd.tcl" or the name of all the
groups this user is member of.

These two new modulefile commands can help to adapt code to specific
users or groups. Like for instance to instantiate a modulefile for
each group the user is member of:

   $ cat /path/to/modulefiles/foo/.modulerc
   #%Module4.6
   foreach grp [module-info usergroups] {
       module-virtual foo/$grp .common
   }
   $ id -G -n
   grp1 grp2 grp3
   $ module avail
   --------------- /path/to/modulefiles ---------------
   foo/grp1  foo/grp2  foo/grp3

"username" and "usergroups" sub-commands of "module-info" modulefile
command are only supported on Unix platform.


Hiding modules
--------------

The newly introduced "module-hide" modulefile command enables to
dynamically hide modulefiles, module aliases or symbolic versions
specified to it:

   $ cat /path/to/modulefiles/bar/.modulerc
   #%Module4.6
   module-version bar/1.0 old
   # hide 'old' symbolic version
   module-hide bar/old
   # hide all version 2 and above
   module-hide bar@2:
   $ cat /path/to/modulefiles/.modulerc
   #%Module4.6
   # hide all versions of foo module
   module-hide foo

"module-hide" commands should be placed in module rc files and can
leverage the Advanced module version specifiers syntax as shown in the
above example.

Hidden modules are excluded from available module search or module
selection unless query refers to hidden module by its exact name:

   $ ml av
   --------------- /path/to/modulefiles ---------------
   bar/1.0  bar/2.0
   $ module load -v foo
   ERROR: Unable to locate a modulefile for 'foo'
   $ module load -v foo/1.0
   Loading foo/1.0
   $ module avail bar/old
   --------------- /path/to/modulefiles ---------------
   bar/1.0(old)

"module-hide" command accepts a "--soft" option to apply a lighter of
hiding to modules:

   $ cat /path/to/modulefiles/qux/.modulerc
   #%Module4.6
   # softly hide all qux modules
   module-hide --soft qux

The soft hiding mode enables to hide modules from full availability
listing yet keeping the ability to select such module for load without
having to use module exact name:

   $ ml av
   --------------- /path/to/modulefiles ---------------
   bar/1.0  bar/2.0
   $ ml av qux
   --------------- /path/to/modulefiles ---------------
   qux/1.0  qux/2.0
   $ module load -v qux
   Loading qux/2.0

Alternatively, a "--hard" option can be set on "module-hide" command
to ensure designated modules do not unveil even if referred by their
exact name:

   $ cat /path/to/modulefiles/qux/.modulerc
   #%Module4.6
   # softly hide all qux modules
   module-hide --soft qux
   # set highest version of qux hard hidden
   module-hide --hard qux/3.0
   $ ml av qux/3.0
   $ ml qux/3.0
   ERROR: Unable to locate a modulefile for 'qux/3.0'

Some users or groups can be set unaffected by hiding mechanism with
the "--not-user" or "--not-group" options:

   $ cat /path/to/modulefiles/quuz/.modulerc
   #%Module4.6
   # hiding does not apply to grp1 and grp2 groups
   module-hide --not-group {grp1 grp2} quuz

   $ id --groups --name
   grp1 grp7
   $ ml av quuz
   --------------- /path/to/modulefiles ---------------
   quuz/1.0  quuz/2.0
   $ ml -v quuz
   Loading quuz/2.0

Hiding mechanism can also be set effective only before or after a
given date time with the "--before" and "--after" options. Accepted
date time format is "YYYY-MM-DD[THH:MM]".

   $ cat /path/to/modulefiles/fum/.modulerc
   #%Module4.6
   # hide only before a given date
   module-hide --hard --before 2020-09-01T12:00 fum/1.0
   # hide only after a given date
   module-hide --hard --after 2020-09-01 fum/2.0

   $ date
   Fri 04 Sep 2020 06:21:48 AM CEST
   $ ml av fum
   --------------- /path/to/modulefiles ---------------
   fum/1.0

Hidden modules can be included in available module searches if option
"--all"/"-a" is set on "avail", "aliases", "whatis" or "search" sub-
commands. Hard hidden modules are unaffected by this option and stay
hidden.

   $ ml av -a
   --------------- /path/to/modulefiles ---------------
   bar/1.0(old)  foo/1.0  fum/1.0   quuz/2.0  qux/2.0
   bar/2.0       foo/2.0  quuz/1.0  qux/1.0


Forbidding use of modules
-------------------------

The "module-forbid" modulefile command is added to dynamically forbid
the evaluation of modulefiles it specifies. When forbidden, a module
cannot be loaded and an access error is returned when an attempt is
made to evaluate it.

   $ cat /path/to/modulefiles/foo/.modulerc
   #%Module4.6
   module-forbid foo@1:
   $ ml foo/1.0
   ERROR: Access to module 'foo/1.0' is denied
   $ ml
   No Modulefiles Currently Loaded.

"module-forbid" statements can be coupled with "module-hide"
statements to hide modules in addition to forbid their use. "module-
forbid" supports the "--not-user", "--not-group", "--before" and "--
after" options to still allow some users or forbid modules before or
after a given date time.

An additional error message can be defined with the "--message" option
to guide for instance users when they try to evaluate a forbidden
module:

   $ cat /path/to/modulefiles/bar/.modulerc
   #%Module4.6
   module-forbid --message {Software bar/1.0 is decommissioned, please now use\
       bar/2.0} --after 2020-09-01 bar/1.0
   $ ml bar/1.0
   ERROR: Access to module 'bar/1.0' is denied
     Software bar/1.0 is decommissioned, please now use bar/2.0

When an evaluated module will soon be forbidden, a message is returned
to the user to warn him/her of the near limit. An additional warning
message can also be defined here with the "--nearly-message" option to
guide users.

   $ cat /path/to/modulefiles/qux/.modulerc
   #%Module4.6
   module-forbid --nearly-message {Version 1.0 will soon expire, please now use\
       version 2.0} --after 2020-09-15 qux/1.0
   $ date
   Tue 08 Sep 2020 06:49:43 AM CEST
   $ ml qux/1.0
   Loading qux/1.0
     WARNING: Access to module will be denied starting '2020-09-15'
       Version 1.0 will soon expire, please now use version 2.0

The range of time the *nearly forbidden* warning appears can be
controlled with the "nearly_forbidden_days" configuration option,
whose value equals to the number of days prior the module starts to be
forbidden. This configuration is set to "14" (days) by default and
this value can be controlled at "configure" time with "--with-nearly-
forbidden-days" option. When the "nearly_forbidden_days" configuration
is set through the "config" sub-command, the
"MODULES_NEARLY_FORBIDDEN_DAYS" environment variable is set.


Tracing module execution
------------------------

The "trace" verbosity is introduced between the "verbose" and "debug"
levels to report details on module searches, resolutions, selections
and evaluations. Trace mode can be enabled by setting the "verbosity"
config to the "trace" value or by using the "-T"/"--trace" command-
line switches.

To specifically render trace messages, the "tr" key is added to the
color palette with a default value of "2" (decreased intensity).

   $ ml -T foo
   Evaluate modulerc: '/path/to/modulefiles/.modulerc'
   Get modules: {foo} matching 'foo' in '/path/to/modulefiles'
   Resolve: 'foo' into 'bar'
   Get modules: {bar bar/1.0} matching 'bar' in '/path/to/modulefiles'
   Select module: 'bar/1.0' (/path/to/modulefiles/bar/1.0) matching 'bar/1.0'

   Loading bar/1.0
     Evaluate modulefile: '/path/to/modulefiles/bar/1.0' as 'bar/1.0'


v4.5
====

This new version is backward-compatible with previous version 4
releases. It fixes bugs but also introduces new functionalities that
are described in this section. See the 4.5 release notes for a
complete list of the changes between Modules v4.4 and v4.5.


ml command
----------

The "ml" command is added to Modules. "ml" is a frontend to the
"module" command that reduces the number of characters to type to
trigger module actions.

With no argument provided "ml" is equivalent to "module list", "ml
foo" corresponds to "module load foo" and "ml -foo" means "module
unload foo":

   $ ml foo
   $ ml
   Currently Loaded Modulefiles:
    1) foo/2
   $ ml -foo
   $ ml
   No Modulefiles Currently Loaded.

Multiple modules to either load or unload can be combined on a single
command. The unloads are first processed then the loads.

"ml" accepts all command-line switches and sub-commands accepted by
"module" command:

   $ ml avail -t foo
   foo/1
   foo/2

This handy interface has been originally developed by the Lmod
project. Having this command line interface also supported on Modules
helps to provide a similar user experience whatever the module
implementation used.


JSON format output
------------------

The "-j" and "--json" command line switches are added for the "avail",
"list", "savelist", "whatis" and "search" module sub-commands. When
set, the output result of these sub-commands is rendered in JSON
format:

   $ module avail --json bar | python -mjson.tool
   {
       "/path/to/modulefiles": {
           "bar/2.3": {
               "name": "bar/2.3",
               "pathname": "/path/to/modulefiles/bar/2.3",
               "symbols": [
                   "default"
               ],
               "type": "modulefile"
           },
           "bar/3.4": {
               "name": "bar/3.4",
               "pathname": "/path/to/modulefiles/bar/3.4",
               "symbols": [],
               "type": "modulefile"
           }
       }
   }
   $ ml whatis -j foo/1.2.3 | python -mjson.tool
   {
       "/path/to/modulefiles": {
           "foo/1.2.3": {
               "name": "foo/1.2.3",
               "whatis": [
                   "The foo/1.2.3 modulefile"
               ]
           }
       }
   }


Improved Windows support
------------------------

A new option to the "./configure" script named "--enable-windows-
support" is introduced to install additional files relative to the
enablement of Modules on the Windows platform. When set, this option
installs "module.cmd", "ml.cmd" and "envml.cmd" scripts in "bindir"
and initialization script "cmd.cmd" in "initdir". With these four
files the Modules installation may be used from either a Unix or a
Windows platform.

"module.cmd", "ml.cmd" and "envml.cmd" scripts respectively provide
the "module", "ml" and "envml" commands for Windows "cmd" terminal
shell, relying on "modulecmd.tcl" script which was already able to
produce shell code for this Windows shell. Initialization script
"cmd.cmd" adds the directory of "module.cmd", "ml.cmd" and "envml.cmd"
to "PATH".

These Windows-specific files are relocatable: "module.cmd", "ml.cmd"
and "envml.cmd" scripts expect to find initialization script "cmd.cmd"
in the "init" directory next to them (to setup Modules-specific
variables in current environment) and "cmd.cmd" expects
"modulecmd.tcl" to be found in "libexec" directory and the 3 commands
in "bin" directory next to it.

Starting from this "4.5" release a distribution zipball is published
to install Modules on Windows. This zip archive ships an install and
an uninstall scripts ("INSTALL.bat" and "UNINSTALL.bat"). The zipball
can be built locally from Modules sources by running "make dist-win".

The Installing Modules on Windows document describes how to install
Modules on Windows from the distribution zipball.


Error stack trace
-----------------

Error messages will now embed a stack trace for unknown errors to help
localize the root cause of issues. This change applies to modulefile
evaluation:

   Loading foo/1.2
     Module ERROR: add-path cannot handle path equals to separator string
           while executing
       "append-path PATH :"
           (file "/path/to/modulefiles/foo/1.2" line 24)
       Please contact <root@localhost>

A stack trace is also returned when an unknown error occurs in
"modulecmd.tcl" script, which facilitates issue report and analysis:

   $ module load bar
   ERROR: invalid command name "badcommand"
         while executing
     "badcommand"
         (procedure "module" line 14)
         invoked from within
     "module load bar"
         ("eval" body line 1)
         invoked from within
     "eval $execcmdlist"
     Please report this issue at https://github.com/cea-hpc/modules/issues


Automatic default and latest symbolic versions
----------------------------------------------

When the implicit default mechanism and the Advanced module version
specifiers are both enabled, a "default" and a "latest" symbolic
versions are automatically defined for each module name.

This new feature gives the ability to select the highest version
available for a module, without knowing beforehand this version name:

   $ module load -v foo@latest
   Loading foo/1.10

The symbolic versions are automatically defined unless a symbolic
version, an alias or a regular module version already exists for these
"default" or "latest" version names.


v4.4
====

This new version is backward-compatible with previous version 4
releases. It fixes bugs but also introduces new functionalities that
are described in this section. See the 4.4 release notes for a
complete list of the changes between Modules v4.3 and v4.4.

Warning:

  Modules configuration option handling has been reworked internally
  to provide a unified way for all options to get initialized,
  retrieved or set. Existing site-specific configuration script should
  be reviewed to make use of the new "getConf", "setConf", "unsetConf"
  and "lappendConf" procedures to manipulate configuration options.


Specify modules in a case insensitive manner
--------------------------------------------

The ability to match module name in a case insensitive manner has been
added. This feature can be enabled at different level with the
following values set to the "icase" configuration option:

* "never": a case sensitive match is applied in any cases

* "search": a case insensitive match is applied to the "avail",
  "whatis" and "paths" sub-commands

* "always": a case insensitive match is applied to search contexts and
  also to the other module sub-commands and modulefile Tcl commands
  for the module specification they receive as argument.

It can help for instance to load a module without knowing the case
used to name its relative modulefile:

   $ module config icase always
   $ module load -v mysoftware
   Loading MySoftware/1.0

Insensitive case match activation can be controlled at configure time
with the "--with-icase" option, which could be passed any of the above
activation levels. This option could be superseded with the
"MODULES_ICASE" environment variable, which could be set through the
**config** sub-command with the "icase" option. Command-line switch
**--icase** supersedes in turns any other icase configurations. When
this command-line switch is passed, "icase" mode equals "always".


Extended default
----------------

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.


Advanced module version specifiers
----------------------------------

The ability to specify finer constraints on module version has been
added to Modules. It enables to filter the module selection to a given
version list or range by specifying after the module name a version
constraint prefixed by the "@" character.

This new feature leverages the version specifier syntax of the Spack
package manager as this syntax covers all the needs for a fine-grained
selection of module versions. It copes very well with command-line
typing, by avoiding characters having a special meaning on shells.
Moreover the users of Spack that also are users of Modules may already
be familiar with this syntax.

The mechanism introduced here is called *advanced module version
specifier* and it can be activated through the new configuration
option "advanced_version_spec". Constraints can be expressed to refine
the selection of module version to:

* a single version with the "@version" syntax, for instance
  "foo@1.2.3" syntax will select module "foo/1.2.3"

* a list of versions with the "@version1,version2,..." syntax, for
  instance "foo@1.2.3,1.10" will match modules "foo/1.2.3" and
  "foo/1.10"

* a range of versions with the "@version1:", "@:version2" and
  "@version1:version2" syntaxes, for instance "foo@1.2:" will select
  all versions of module "foo" greater than or equal to "1.2",
  "foo@:1.3" will select all versions less than or equal to "1.3" and
  "foo@1.2:1.3" matches all versions between "1.2" and "1.3" including
  "1.2" and "1.3" versions

This new feature enables for instance to list available versions of
module "foo" higher or equal to "1.2":

   $ module config advanced_version_spec 1
   $ 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 av foo@1.2:
   --------------- /path/to/modulefiles ---------------
   foo/1.2.1  foo/1.2.3  foo/1.10

Then choose to load for instance a version higher than or equal to
"1.2" and less than or equal to "1.3". Default version is selected if
it corresponds to a version included in the range, elsewhere the
highest version (also called latest version or implicit default) is
selected:

   $ module load -v foo@1.2:1.3
   Loading foo/1.2.3

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

   $ module config implicit_default 0
   $ module load -v foo@1.2:1.3
   ERROR: No default version defined for 'foo@1.2:1.3'

When advanced module version specifier is enabled, it 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
smoother dependencies between modules:

   $ module show bar@:2
   ----------------------------------------------------------
   /path/to/modulefiles/bar/2.3:

   prereq          foo@1.1.10,1.2.1
   ----------------------------------------------------------
   $ module load --auto bar@:2
   Loading bar/2.3
     Loading requirement: foo/1.2.1

Advanced specification of single version or list of versions may
benefit from the activation of the Extended default mechanism (range
of versions natively handles abbreviated versions):

   $ module config extended_default 1
   $ module load -v foo@1.2
   Loading foo/1.2.3
   $ module unload -v foo @1.2,1.5
   Unloading foo/1.2.3

Advanced module version specifier activation can be controlled at
configure time with the "--enable-advanced-version-spec" option. This
option could be superseded with the "MODULES_ADVANCED_VERSION_SPEC"
environment variable, which could be set through the **config** sub-
command with the "advanced_version_spec" option.


v4.3
====

This new version is backward-compatible with previous version 4
releases. It fixes bugs but also introduces new functionalities that
are described in this section. See the 4.3 release notes for a
complete list of the changes between Modules v4.2 and v4.3.


Modulepath rc file
------------------

A ".modulerc" file found at the root of an enabled modulepath
directory is now evaluated when modulepath is walked through to locate
modulefiles. This modulepath rc file gives for instance the ability to
define module alias whose name does not correspond to any module
directory in this modulepath. Thus this kind of module alias would not
be found unless if it is defined at the modulepath global scope.


Further I/O operations optimization
-----------------------------------

Additional work has been performed to save a significant number of
filesystem I/O operations made to search and evaluate modulefiles.

When fully read, the content of a modulefile is now cached in memory
to avoid new I/O operations in case this modulefile should be read one
more time during the same module command evaluation.

Except for "path", "paths", "list", "avail" and "aliases" module
commands always fully read a modulefile whether its full content is
needed or just its header to verify its validity. This way modulefiles
are only read once on commands that first check modulefile validity
then read again valid files to get their full content.

Last but not least, Modules Tcl extension library is introduced to
extend the Tcl language in order to provide more optimized I/O
commands to read a file or a directory content than native Tcl
commands do. This library is built and enabled in "modulecmd.tcl"
script with "--enable-libtclenvmodules" configure argument (it is
enabled by default). As this library is written in C, it must be
compiled and "--with-tcl" or "--with-tclinclude" configure arguments
may be used to indicate where to find Tcl development files.

Modules Tcl extension library greatly reduces the number of filesystem
I/O operations by removing unneeded "ioctl", "fcntl" and "lstat"
system calls done (by Tcl "open" command) to read each modulefile.
Directory content read is also improved by fetching hidden and regular
files in one pass. Moreover ".modulerc" and ".version" read access is
tested only if these files are found in the directory.


Colored output
--------------

The ability to graphically enhance some part of the produced output
has been added to improve readability. Among others, error, warning
and info message prefixes can be colored as well as modulepath, module
alias and symbolic version.

Color mode can be set to "never", "auto" or "always". When color mode
is set to "auto", output is colored only if the standard error output
channel is attached to a terminal.

Default color mode could be controlled at configure time with the "--
enable-color" and the "--disable-color" option, which respectively
correspond to the "auto" and "never" color mode. This default mode
could be superseded with the "CLICOLOR", "CLICOLOR_FORCE" and
"MODULES_COLOR" environment variables and the "--color" command-line
switch.

Color to apply to each element can be controlled with the
"MODULES_COLORS" environment variable or the "--with-dark-background-
colors" and "--with-light-background-colors" configure options. These
variable and options take as value a colon-separated list in the same
fashion "LS_COLORS" does. In this list, output item that should be
highlighted is designated by a key which is associated to a Select
Graphic Rendition (SGR) code.

The "MODULES_TERM_BACKGROUND" environment variable and the "--with-
terminal-background" configure option help Modules to determine if the
color set for dark background or the color set for light background
should be used to color output in case no specific color set is
defined with the "MODULES_COLORS" variable.

Output items able to be colorized and their relative key are:
highlighted element ("hi"), debug information ("db"), tag separator
("se"); Error ("er"), warning ("wa"), module error ("me") and info
("in") message prefixes; Modulepath ("mp"), directory ("di"), module
alias ("al"), module symbolic version ("sy"), module "default" version
("de") and modulefile command ("cm").

For instance the default color set for a terminal with dark background
is defined to:

   hi=1:db=2:se=2:er=91:wa=93:me=95:in=94:mp=1;94:di=94:al=96:sy=95:de=4:cm=92

When colored output is enabled and a specific graphical rendition is
defined for module *default* version, the "default" symbol is omitted
and instead the defined graphical rendition is applied to the relative
modulefile. When colored output is enabled and a specific graphical
rendition is defined for module alias, the "@" symbol is omitted.

"CLICOLOR" and "CLICOLOR_FORCE" environment variables are also honored
to define color mode. The "never" mode is set if "CLICOLOR" equals to
"0". If "CLICOLOR" is set to another value, it corresponds to the
"auto" mode. The "always" mode is set if "CLICOLOR_FORCE" is set to a
value different than "0". Color mode set with these two variables is
superseded by mode set with "MODULES_COLOR" environment variable.


Configure modulecmd with config sub-command
-------------------------------------------

The **config** sub-command has been added to "module" to help getting
or setting the **modulecmd.tcl** options. With no additional command-
line argument, this sub-command reports the current value of all
existing options with a mention to indicate if this value has been
overridden from a command-line switch or from an environment variable.

See the description of this sub-command in the module man page for a
complete reference on existing configuration options.

Most of the options can be altered by passing the option name and a
value to the sub-command. Setting an option by this mean overrides its
default value, set at installation time in **modulecmd.tcl** script,
by defining the environment variable which supersedes this default.:

   $ module config auto_handling 1
   $ module config auto_handling
   Modules Release 4.3.0 (2019-07-26)

   - Config. name ---------.- Value (set by if default overridden) ---------------
   auto_handling             1 (env-var)

Setting options with "module config" could be done in the Modules
initialization RC file to change default value of options when
"module" command is initialized.

When command-line switch "--reset" and an option name is passed to the
**config** sub-command, it restores default value for configuration
option by unsetting related environment variable.

With command-line switch "--dump-state", the **config** sub-command
reports, in addition to currently set options, the current state of
**modulecmd.tcl** script and Modules-related environment variables.
Providing the output of the "module config --dump-state" command when
submitting an issue to the Modules project will help to analyze the
situation.


Control module command verbosity
--------------------------------

The ability to control message verbosity has been added so "module"
command can be configured whether it should display more or less
information. Available verbosity levels from the least to the most
verbose are:

* "silent": turn off error, warning and informational messages but
  does not affect module command output result.

* "concise": enable error and warning messages but disable
  informational messages.

* "normal": turn on informational messages, like a report of the
  additional module evaluations triggered by loading or unloading
  modules, aborted evaluation issues or a report of each module
  evaluation occurring during a **restore** or **source** sub-
  commands.

* "verbose": add additional informational messages, like a systematic
  report of the loading or unloading module evaluations.

* "debug": print debugging messages about module command execution.

Default verbosity level can be controlled at configure time with the "
--with-verbosity" option, which could be passed any of the above level
names. This default verbosity level could be superseded with the
"MODULES_VERBOSITY" environment variable, which could be set through
the **config** sub-command with the "verbosity" option. Command-line
switches **--silent**, **--verbose** and **--debug** supersede in
turns any other verbosity configuration to respectively set module
command silent, verbose or in debug mode.


Other new sub-commands, command-line switches and environment variables
-----------------------------------------------------------------------

* The **avail** sub-command gets two new command-line switches:
  **--indepth** and **--no-indepth**. These options control whether
  search results should recursively include or not modulefiles from
  directories matching search query. Shell completion scripts have
  been updated to complete available modulefiles in the no in depth
  mode.

* The **MODULES_AVAIL_INDEPTH** environment variable defines if the
  **avail** sub-command should include or exclude by default the
  modulefiles from directories matching search query. Its value is
  superseded by the use of the **--indepth** and **--no-indepth**
  command-line switches.

* The **clear** sub-command, which was available on Modules version
  3.2, has been reintroduced. This sub-command resets the Modules
  runtime information but does not apply further changes to the
  environment at all. This sub-command now leverages the **--force**
  command-line switch to skip its confirmation dialog.

* The **MODULES_SITECONFIG** environment variable defines an
  additional siteconfig script which is loaded if it exists after the
  siteconfig script configured at build time in "modulecmd.tcl". This
  ability is enabled by default and could be disabled with configure
  option "--with-locked-configs=extra_siteconfig".

* The **MODULES_UNLOAD_MATCH_ORDER** environment variable sets whether
  the firstly or the lastly loaded module should be selected for
  unload when multiple loaded modules match unload request. Configure
  option "--with-unload-match-order" defines this setting which can be
  superseded by the environment variable. By default, lastly loaded
  module is selected and it is recommended to keep this behavior when
  used modulefiles express dependencies between each other.

* The **MODULES_IMPLICIT_DEFAULT** environment variable sets whether
  an implicit default version should be defined for modules with no
  default version explicitly defined. When enabled, which is the
  default behavior, a module version is automatically selected (latest
  one) when the generic name of the module is passed. When implicit
  default is disabled and no default version is explicitly defined for
  a module, the name of this module to evaluate should be fully
  qualified elsewhere an error is returned. Configure option "--
  enable-implicit-default" defines this setting which can be
  superseded by the environment variable. This superseding mechanism
  can be disabled with configure option "--with-locked-
  configs=implicit_default".

* The **MODULES_SEARCH_MATCH** environment variable defines the
  matching style to perform when searching for available modules. With
  **starts_with** value, modules whose name begins by search query
  string are returned. When search match style is set to **contains**,
  modules returned are those whose fully qualified name contains
  search query string. Configure option "--with-search-match" defines
  this setting which can be superseded by the environment variable,
  which in turns can be superseded by the **--starts-with** and
  **--contains** command-line switches of **avail** module sub-
  command.

* The **MODULES_SET_SHELL_STARTUP** environment variable controls
  whether or not shell startup file should be set to ensure "module"
  command is defined once shell has been initialized. When enabled,
  the "ENV" and "BASH_ENV" environment variables are set, when
  "module" function is defined, to the Modules bourne shell
  initialization script. Configure options "--enable-set-shell-
  startup" and "--disable-set-shell-startup" define this setting which
  can be superseded by the environment variable.

* When initializing the "module" command in a shell session,
  initialization configuration files stored in the defined
  configuration directory are taken into account if present instead of
  the configuration files stored in the initialization script
  directory. When they are stored in the configuration directory,
  these configuration files are named "initrc" and "modulespath"
  instead of respectively "modulerc" and ".modulespath". The location
  of the installation of those files can be controlled with configure
  option "--with-initconf-in", which accepts "etcdir" and "initdir"
  values.

* The **MODULES_WA_277** environment variable helps to define an
  alternative "module" alias on Tcsh shell when set to *1*. It
  workarounds an issue on Tcsh history mechanism occurring with
  default "module" command alias: erroneous history entries are
  recorded each time the "module" command is called. However the
  alternative definition of the module alias weakens shell evaluation
  of the code produced by modulefiles. Characters with special meaning
  for Tcsh shell (like *{* and *}*) may not be used anymore in shell
  alias definition elsewhere the evaluation of the code produced by
  modulefiles will return a syntax error.


v4.2
====

This new version is backward-compatible with previous version 4
releases. It fixes bugs but also introduces new functionalities that
are described in this section. See the 4.2 release notes for a
complete list of the changes between Modules v4.1 and v4.2.


Modulefile conflict constraints consistency
-------------------------------------------

With the **conflict** modulefile command, a given modulefile can list
the other modulefiles it conflicts with. To load this modulefile, the
modulefiles it conflicts with cannot be loaded.

This constraint was until now satisfied when loading the modulefile
declaring the **conflict** but it vanished as soon as this modulefile
was loaded. In the following example "a" modulefile declares a
conflict with "b":

   $ module load b a
   WARNING: a cannot be loaded due to a conflict.
   HINT: Might try "module unload b" first.
   $ module list
   Currently Loaded Modulefiles:
    1) b
   $ module purge
   $ module load a b
   $ module list
   Currently Loaded Modulefiles:
    1) a   2) b

Consistency of the declared **conflict** is now ensured to satisfy
this constraint even after the load of the modulefile declaring it.
This is achieved by keeping track of the conflict constraints of the
loaded modulefiles in an environment variable called
"MODULES_LMCONFLICT":

   $ module load a b
   ERROR: WARNING: b cannot be loaded due to a conflict.
   HINT: Might try "module unload a" first.
   $ module list
   Currently Loaded Modulefiles:
    1) a

An environment variable is used to keep track of this conflict
information to proceed the same way than used to keep track of the
loaded modulefiles with the "LOADEDMODULES" environment variable.

In case a conflict constraint toward a modulefile is set by an already
loaded modulefile, loading the conflicting modulefile will lead to a
load evaluation attempt in order for this modulefile to get the chance
to solve the constraint violation. If at the end of the load
evaluation, the conflict has not been solved, modulefile load will be
discarded.

Warning:

  On versions "4.2.0" and "4.2.1", a conflict constraint set by an
  already loaded modulefile forbade the load of the conflicting
  modulefile. This has been changed starting version "4.2.2" to better
  cope with behaviors of previous Modules version: an evaluation
  attempt of the conflicting modulefile is made to give it the
  opportunity to solve this conflict by using **module unload**
  modulefile command.


Modulefile prereq constraints consistency
-----------------------------------------

With the **prereq** modulefile command, a given modulefile can list
the other modulefiles it pre-requires. To load this modulefile, the
modulefiles it pre-requires must be loaded prior its own load.

This constraint was until now satisfied when loading the modulefile
declaring the **prereq** but, as for the declared **conflict**, it
vanished as soon as this modulefile was loaded. In the following
example "c" modulefile declares a prereq on "a":

   $ module load c
   WARNING: c cannot be loaded due to missing prereq.
   HINT: the following module must be loaded first: a
   $ module list
   No Modulefiles Currently Loaded.
   $ module load a c
   $ module list
   Currently Loaded Modulefiles:
    1) a   2) c
   $ module unload a
   $ module list
   Currently Loaded Modulefiles:
    1) c

Consistency of the declared **prereq** is now ensured to satisfy this
constraint even after the load of the modulefile declaring it. This is
achieved, like for the conflict consistency, by keeping track of the
prereq constraints of the loaded modulefiles in an environment
variable called "MODULES_LMPREREQ":

   $ module load a c
   $ module list
   Currently Loaded Modulefiles:
    1) a   2) c
   $ module unload a
   ERROR: WARNING: a cannot be unloaded due to a prereq.
   HINT: Might try "module unload c" first.
   $ module list
   Currently Loaded Modulefiles:
    1) a   2) c


By-passing module defined constraints
-------------------------------------

The ability to by-pass a **conflict** or a **prereq** constraint
defined by modulefiles is introduced with the "--force" command line
switch ("-f" for short notation) for the **load**, **unload** and
**switch** sub-commands.

With this new command line switch, a given modulefile is loaded even
if it conflicts with other loaded modulefiles or even if the
modulefiles it pre-requires are not loaded. Some example reusing the
same modulefiles "a", "b" and "c" than above:

   $ module load b
   $ module load --force a
   WARNING: a conflicts with b
   $ module list
   Currently Loaded Modulefiles:
    1) b   2) a
   $ module purge
   $ module load --force c
   WARNING: c requires a loaded
   $ module list
   Currently Loaded Modulefiles:
    1) c

"--force" also enables to unload a modulefile required by another
loaded modulefiles:

   $ module load a c
   $ module list
   Currently Loaded Modulefiles:
    1) a   2) c
   $ module unload --force a
   WARNING: a is required by c
   $ module list
   Currently Loaded Modulefiles:
    1) c

In a situation where some of the loaded modulefiles have unsatisfied
constraints corresponding to the **prereq** and **conflict** they
declare, the **save** and **reload** sub-commands do not perform and
return an error.


Automated module handling mode
------------------------------

An automatic management of the dependencies between modulefiles has
been added and it is called *automated module handling mode*. This new
mode consists in additional actions triggered when loading or
unloading a modulefile to satisfy the constraints it declares.

When loading a modulefile, following actions are triggered:

* Requirement Load (ReqLo): load of the modulefiles declared as a
  **prereq** of the loading modulefile.

* Dependent Reload (DepRe): reload of the modulefiles declaring a
  **prereq** onto loaded modulefile or declaring a **prereq** onto a
  modulefile part of this reloading batch.

When unloading a modulefile, following actions are triggered:

* Dependent Unload (DepUn): unload of the modulefiles declaring a non-
  optional **prereq** onto unloaded modulefile or declaring a non-
  optional **prereq** onto a modulefile part of this unloading batch.
  A **prereq** modulefile is considered optional if the **prereq**
  definition order is made of multiple modulefiles and at least one
  alternative modulefile is loaded.

* Useless Requirement Unload (UReqUn): unload of the **prereq**
  modulefiles that have been automatically loaded for either the
  unloaded modulefile, an unloaded dependent modulefile or a
  modulefile part of this useless requirement unloading batch.
  Modulefiles are added to this unloading batch only if they are not
  required by any other loaded modulefiles. "MODULES_LMNOTUASKED"
  environment variable helps to keep track of these automatically
  loaded modulefiles and to distinguish them from modulefiles asked by
  user.

* Dependent Reload (DepRe): reload of the modulefiles declaring a
  **conflict** or an optional **prereq** onto either the unloaded
  modulefile, an unloaded dependent or an unloaded useless requirement
  or declaring a **prereq** onto a modulefile part of this reloading
  batch.

In case a loaded modulefile has some of its declared constraints
unsatisfied (pre-required modulefile not loaded or conflicting
modulefile loaded for instance), this loaded modulefile is excluded
from the automatic reload actions described above.

For the specific case of the **switch** sub-command, where a
modulefile is unloaded to then load another modulefile. Dependent
modulefiles to Unload are merged into the Dependent modulefiles to
Reload that are reloaded after the load of the switched-to modulefile.

This automated module handling mode integrates concepts (like the
Dependent Reload mechanism) of the Flavours extension, which was
designed for Modules compatibility version. As a whole, automated
module handling mode can be seen as a generalization and as an
expansion of the Flavours concepts.

This new feature can be controlled at build time with the "--enable-
auto-handling" configure option. This default configuration can be
superseded at run-time with the "MODULES_AUTO_HANDLING" environment
variable or the command line switches "--auto" and "--no-auto".

By default, automated module handling mode is disabled and will stay
so until the next major release version (5.0) where it will be enabled
by default. This new feature is currently considered experimental and
the set of triggered actions will be refined over the next feature
releases.


Consistency of module load/unload commands in modulefile
--------------------------------------------------------

With the **module load** modulefile command, a given modulefile can
automatically load a modulefile it pre-requires. Similarly with the
**module unload** modulefile command, a given modulefile can
automatically unload a modulefile it conflicts with.

Both commands imply additional actions on the loaded environment
(loading or unloading extra modulefiles) that should cope with the
constraints defined by the loaded environment.

Additionally **module load** and **module unload** modulefile commands
express themselves constraints on loaded environment that should stay
satisfied to ensure consistency.

To ensure the consistency of **module load** modulefile command once
the modulefile defining it has been loaded, this command is
assimilated to a **prereq** command. Thus the defined constraint is
recorded in the "MODULES_LMPREREQ" environment variable. Same approach
is used for **module unload** modulefile command which is assimilated
to a **conflict** command. Thus the defined constraint is recorded in
the "MODULES_LMCONFLICT" environment variable.

To ensure the consistency of the loaded environment, the additional
actions of the **module load** and **module unload** modulefile
commands have been adapted in particular situations:

* When unloading modulefile, **module load** command will unload the
  modulefile it targets only if no other loaded modulefile requires it
  and if this target has not been explicitly loaded by user.

* When unloading modulefile, **module unload** command does nothing as
  the relative conflict registered at load time ensure environment
  consistency and will forbid conflicting modulefile load.

Please note that loading and unloading results may differ than from
previous Modules version now that consistency is checked:

* Modulefile targeted by a **module load** modulefile command may not
  be able to load due to a registered conflict in the currently loaded
  environment. Which in turn will break the load of the modulefile
  declaring the **module load** command.

* Modulefile targeted by a **module unload** modulefile command may
  not be able to unload due to a registered prereq in the loaded
  environment. Which in turn will break the load of the modulefile
  declaring the **module unload** command.

* If automated module handling mode is enabled, **module load**
  modulefile command is interpreted when unloading modulefile as part
  of the Useless Requirement Unload (UReqUn) mechanism not through
  modulefile evaluation. As a consequence, an error occurring when
  unloading the modulefile targeted by the **module load** command
  does not break the unload of the modulefile declaring this command.
  Moreover unload of the **module load** targets is done in the
  reverse loaded order, not in the **module load** command definition
  order.


Modulefile alias and symbolic modulefile name consistency
---------------------------------------------------------

With the **module-alias** and **module-version** modulefile commands,
alternative names can be given to a modulefile. When these names are
used to load for instance a modulefile, they are resolved to the
modulefile they target which is then processed for the load action.

Until now, the alias and symbolic version names were correctly
resolved for the **load** and **unload** actions and also for the
querying sub-commands (like **avail** or **whatis**). However this
alternative name information vanishes once the modulefile it resolves
to is loaded. As a consequence there was no consistency over these
alternative designations. In the following example "f" modulefile
declares a conflict on "e" alias which resolves to "d" modulefile:

   $ module load e
   $ module list
   Currently Loaded Modulefiles:
    1) d
   $ module info-loaded e
   $ module load f
   $ module list
   Currently Loaded Modulefiles:
    1) d   2) f

Consistency of the alternative names set on a modulefile with
**module-alias** and **module-version** commands is now ensured to
enable modulefile commands **prereq**, **conflict**, **is-loaded** and
**module-info loaded** using these alternative designations as
argument. This consistency is achieved, like for the conflict and
prereq consistencies, by keeping track of the alternative names of the
loaded modulefiles in an environment variable called
"MODULES_LMALTNAME":

   $ module load e
   $ module list
   Currently Loaded Modulefiles:
    1) d
   $ module info-loaded e
   d
   $ module load f
   WARNING: f cannot be loaded due to a conflict.
   HINT: Might try "module unload e" first.
   $ module list
   Currently Loaded Modulefiles:
    1) d


Environment variable change through modulefile evaluation context
-----------------------------------------------------------------

All environment variable edition commands ("setenv", "unsetenv",
"append-path", "prepend-path" and "remove-path") have been updated to:

* Reflect environment variable value change on the environment of the
  current modulefile Tcl interpreter. So using "$env(VAR)" will return
  the currently defined value for environment variable "VAR", not the
  one found prior modulefile evaluation.

* Clear environment variable content instead of unsetting it on the
  environment of the current modulefile Tcl interpreter to avoid
  raising error about accessing an undefined element in "$env()". Code
  is still produced to purely unset environment variable in shell
  environment.

Exception is made for the "whatis" evaluation mode: environment
variables targeted by variable edition commands are not set to the
defined value in the evaluation context during this "whatis"
evaluation. These variables are only initialized to an empty value if
undefined. This exception is made to save performances on this global
evaluation mode.


Express Modules compatibility of modulefile with versioned magic cookie
-----------------------------------------------------------------------

Any modulefile should start with the "#%Module" file signature (also
called the Modules magic cookie) and sometimes a version number may be
placed right after this string. Until now this version number
corresponded to a modulefile format version but it was never checked.

Starting with this new Modules release, this version number reflects
the minimum version of Modules required to interpret the modulefile.
If the version number is set along the magic cookie string it is now
checked and the modulefile is interpreted only if Modules version is
greater or equal to this version number. For instance, if a modulefile
begins with the "#%Module4.3" string, it can only be evaluated by
Modules version 4.3 and above. Elsewhere the modulefile is ignored
like files without the "#%Module" magic cookie set.


Improved module message report
------------------------------

Module sub-commands like "load", "unload" or "switch", may perform
multiple load or unload modulefile evaluations in a row. Also these
kind of evaluation modes may sometimes trigger additional load or
unload evaluations, when for instance a modulefile contains a "module
load" command.

To improve the readability of the module messages produced relatively
to a load or an unload evaluation, these messages are now stacked
under a *Loading* or an *Unloading* message block that gathers all the
messages produced for a given modulefile evaluation:

   $ module load --no-auto foo
   Loading foo/1.2
     ERROR: foo/1.2 cannot be loaded due to missing prereq.
       HINT: the following module must be loaded first: bar/4.5

In addition, foreground "load", "unload", "switch" and "restore"
actions (i.e., asked on the command-line) now report a summary of the
additional load and unload evaluations that were eventually triggered
in the process:

   $ module load --auto foo
   Loading foo/1.2
     Loading requirement: bar/4.5


New modulefile commands
-----------------------

2 new modulefile Tcl commands have been introduced:

* **set-function**: define a shell function on sh-kind and fish
  shells.

* **unset-function**: unset a shell function on sh-kind and fish
  shells.


v4.1
====

This new version is backward-compatible with previous version 4
releases. It fixes bugs but also introduces new functionalities that
are described in this section. See the 4.1 release notes for a
complete list of the changes between Modules v4.0 and v4.1.


Virtual modules
---------------

A virtual module stands for a module name associated to a modulefile.
The modulefile is the script interpreted when loading or unloading the
virtual module which appears or can be found with its virtual name.

The **module-virtual** modulefile command is introduced to give the
ability to define these virtual modules. This new command takes a
module name as first argument and a modulefile location as second
argument:

   module-virtual app/1.2.3 /path/to/virtualmod/app

With this feature it is now possible to dynamically define modulefiles
depending on the context.


Extend module command with site-specific Tcl code
-------------------------------------------------

"module" command can now be extended with site-specific Tcl code.
"modulecmd.tcl" now looks at a **siteconfig.tcl** file in an "etcdir"
defined at configure time (by default "$prefix/etc"). If it finds this
Tcl script file, it is sourced within "modulecmd.tcl" at the beginning
of the main procedure code.

"siteconfig.tcl" enables to supersede any global variable or procedure
definitions made in "modulecmd.tcl" with site-specific code. A module
sub-command can for instance be redefined to make it fit local needs
without having to touch the main "modulecmd.tcl".


Quarantine mechanism to protect module execution
------------------------------------------------

To protect the module command run-time environment from side effect
coming from the current environment definition a quarantine mechanism
is introduced. This mechanism, sets within module function definition
and shell initialization script, modifies the "modulecmd.tcl" run-time
environment to sanitize it.

The mechanism is piloted by environment variables. First of all
"MODULES_RUN_QUARANTINE", a space-separated list of environment
variable names. Every variable found in "MODULES_RUN_QUARANTINE" will
be set in quarantine during the "modulecmd.tcl" run-time. Their value
will be set empty or set to the value of the corresponding
"MODULES_RUNENV_<VAR>" environment variable if defined. Once
"modulecmd.tcl" is started it restores quarantine variables to their
original values.

"MODULES_RUN_QUARANTINE" and "MODULES_RUNENV_<VAR>" environment
variables can be defined at build time by using the following
configure option:

   --with-quarantine-vars='VARNAME[=VALUE] ...'

Quarantine mechanism is available for all supported shells except
"csh" and "tcsh".


Pager support
-------------

The informational messages Modules sends on the *stderr* channel may
sometimes be quite long. This is especially the case for the avail
sub-command when hundreds of modulefiles are handled. To improve the
readability of those messages, *stderr* output can now be piped into a
paging command.

This new feature can be controlled at build time with the "--with-
pager" and "--with-pager-opts" configure options. Default pager
command is set to "less" and its relative options are by default
"-eFKRX". Default configuration can be supersedes at run-time with
"MODULES_PAGER" environment variables or command-line switches ("--no-
pager", "--paginate").

Warning:

  On version "4.1.0", the "PAGER" environment variable was taken in
  consideration to supersede pager configuration at run-time. Since
  version "4.1.1", "PAGER" environment variable is ignored to avoid
  side effects coming from the system general pager configuration.


Module function to return value in scripting languages
------------------------------------------------------

On Tcl, Perl, Python, Ruby, CMake and R scripting shells, module
function was not returning value and until now an occurred error led
to raising a fatal exception.

To make "module" function more friendly to use on these scripting
shells it now returns a value. False in case of error, true if
everything goes well.

As a consequence, returned value of a module sub-command can be
checked. For instance in Python:

   if module('load', 'foo'):
     # success
   else:
     # failure


New modulefile commands
-----------------------

4 new modulefile Tcl commands have been introduced:

* **is-saved**: returns true or false whether a collection,
  corresponding to currently set collection target, exists or not.

* **is-used**: returns true or false whether a given directory is
  currently enabled in "MODULEPATH".

* **is-avail**: returns true or false whether a given modulefile
  exists in currently enabled module paths.

* **module-info loaded**: returns the exact name of the modulefile
  currently loaded corresponding to the name argument.

Multiple collections, paths or modulefiles can be passed respectively
to "is-saved", "is-used" and "is-avail" in which case true is returned
if at least one argument matches condition (acts as a OR boolean
operation). No argument may be passed to "is-loaded", "is-saved" and
"is-used" commands to return if anything is respectively loaded, saved
or used.

If no loaded modulefile matches the "module-info loaded" query, an
empty string is returned.


New module sub-commands
-----------------------

Modulefile-specific commands are sometimes wished to be used outside
of a modulefile context. Especially for the commands managing path
variables or commands querying current environment context. So the
following modulefile-specific commands have been made reachable as
module sub-commands with same arguments and properties as if called
from within a modulefile:

* **append-path**

* **prepend-path**

* **remove-path**

* **is-loaded**

* **info-loaded**

The "is-loaded" sub-command returns a boolean value. Small Python
example:

   if module('is-loaded', 'app'):
     print 'app is loaded'
   else:
     print 'app not loaded'

"info-loaded" returns a string value and is the sub-command
counterpart of the "module-info loaded" modulefile command:

   $ module load app/0.8
   $ module info-loaded app
   app/0.8


v4.0
====

Major evolution occurs with this v4.0 release as the traditional
*module* command implemented in C is replaced by the native Tcl
version. This full Tcl rewrite of the Modules package was started in
2002 and has now reached maturity to take over the binary version.
This flavor change enables to refine and push forward the *module*
concept.

This document provides an outlook of what is changing when migrating
from v3.2 to v4.0 by first describing the introduced new features.
Both v3.2 and v4.0 are quite similar and transition to the new major
version should be smooth. Slights differences may be noticed in a few
use-cases. So the second part of the document will help to learn about
them by listing the features that have been discontinued in this new
major release or the features where a behavior change can be noticed.


New features
------------

On its overall this major release brings a lot more robustness to the
*module* command with now more than 4000 non-regression tests crafted
to ensure correct operations over the time. This version 4.0 also
comes with fair amount of improved functionalities. The major new
features are described in this section.


Additional shells supported
~~~~~~~~~~~~~~~~~~~~~~~~~~~

Modules v4 introduces support for **fish**, **lisp**, **tcl** and
**R** code output.


Non-zero exit code in case of error
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

All module sub-commands will now return a non-zero exit code in case
of error whereas Modules v3.2 always returned zero exit code even if
issue occurred.


Output redirect
~~~~~~~~~~~~~~~

Traditionally the *module* command output text that should be seen by
the user on *stderr* since shell commands are output to *stdout* to
change shell's environment. Now on *sh*, *bash*, *ksh*, *zsh* and
*fish* shells, output text is redirected to *stdout* after shell
command evaluation if shell is in interactive mode.


Filtering avail output
~~~~~~~~~~~~~~~~~~~~~~

Results obtained from the **avail** sub-command can now be filtered to
only get the default version of each module name with use of the
**--default** or **-d** command line switch. Default version is either
the explicitly set default version or the highest numerically sorted
modulefile or module alias if no default version set.

It is also possible to filter results to only get the highest
numerically sorted version of each module name with use of the
**--latest** or **-L** command line switch.


Extended support for module alias and symbolic version
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Module aliases are now included in the result of the **avail**,
**whatis** and **apropos** sub-commands. They are displayed in the
module path section where they are defined or in a *global/user
modulerc* section for aliases set in user's or global "modulerc" file.
A **@** symbol is added in parenthesis next to their name to
distinguish them from modulefiles.

Search may be performed with an alias or a symbolic version-name
passed as argument on **avail**, **whatis** and **apropos** sub-
commands.

Modules v4 resolves module alias or symbolic version passed to
**unload** command to then remove the loaded modulefile pointed by the
mentioned alias or symbolic version.

A symbolic version sets on a module alias is now propagated toward the
resolution path to also apply to the relative modulefile if it still
correspond to the same module name.


Hiding modulefiles
~~~~~~~~~~~~~~~~~~

Visibility of modulefiles can be adapted by use of file mode bits or
file ownership. If a modulefile should only be used by a given subset
of persons, its mode an ownership can be tailored to provide read
rights to this group of people only. In this situation, module only
reports the modulefile, during an **avail** command for instance, if
this modulefile can be read by the current user.

These hidden modulefiles are simply ignored when walking through the
modulepath content. Access issues (permission denied) occur only when
trying to access directly a hidden modulefile or when accessing a
symbol or an alias targeting a hidden modulefile.


Improved modulefiles location
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

When looking for an implicit default in a modulefile directory,
aliases are now taken into account in addition to modulefiles and
directories to determine the highest numerically sorted element.

Modules v4 resolves module alias or symbolic version when it points to
a modulefile located in another modulepath.

Access issues (permission denied) are now distinguished from find
issues (cannot locate) when trying to access directly a directory or a
modulefile as done on **load**, **display** or **whatis** commands. In
addition, on this kind of access not readable ".modulerc" or
".version" files are ignored rather producing a missing magic cookie
error.


Module collection
~~~~~~~~~~~~~~~~~

Modules v4 introduces support for module *collections*. Collections
describe a sequence of **module use** then **module load** commands
that are interpreted by Modules to set the user environment as
described by this sequence. When a collection is activated, with the
**restore** sub-command, modulepaths and loaded modules are unused or
unloaded if they are not part or if they are not ordered the same way
as in the collection.

Collections are generated by the **save** sub-command that dumps the
current user environment state in terms of modulepaths and loaded
modules. By default collections are saved under the "$HOME/.module"
directory. Collections can be listed with **savelist** sub-command,
displayed with **saveshow** and removed with **saverm**.

Collections may be valid for a given target if they are suffixed. In
this case these collections can only be restored if their suffix
correspond to the current value of the "MODULES_COLLECTION_TARGET"
environment variable. Saving collection registers the target footprint
by suffixing the collection filename with
".$MODULES_COLLECTION_TARGET".


Path variable element counter
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Modules 4 provides path element counting feature which increases a
reference counter each time a given path entry is added to a given
path-like environment variable. As consequence a path entry element is
removed from a path-like variable only if the related element counter
is equal to 1. If this counter is greater than 1, path element is kept
in variable and reference counter is decreased by 1.

This feature allows shared usage of particular path elements. For
instance, modulefiles can append "/usr/local/bin" to "PATH", which is
not unloaded until all the modulefiles that loaded it unload too.


Optimized I/O operations
~~~~~~~~~~~~~~~~~~~~~~~~

Substantial work has been done to reduce the number of I/O operations
done during global modulefile analysis commands like **avail** or
**whatis**. "stat", "open", "read" and "close" I/O operations have
been cut down to the minimum required when walking through the
modulepath directories to check if files are modulefiles or to resolve
module aliases.

Interpretation of modulefiles and modulerc are handled by the minimum
required Tcl interpreters. Which means a configured Tcl interpreter is
reused as much as possible between each modulefile interpretation or
between each modulerc interpretation.


Sourcing modulefiles
~~~~~~~~~~~~~~~~~~~~

Modules 4 introduces the possibility to **source** a modulefile rather
loading it. When it is sourced, a modulefile is interpreted into the
shell environment but then it is not marked loaded in shell
environment which differ from **load** sub-command.

This functionality is used in shell initialization scripts once
**module** function is defined. There the "etc/modulerc" modulefile is
sourced to setup the initial state of the environment, composed of
*module use* and *module load* commands.


Removed features and substantial behavior changes
-------------------------------------------------

Following sections provide list of Modules v3.2 features that are
discontinued on Modules v4 or features with a substantial behavior
change that should be taken in consideration when migrating to v4.


Package initialization
~~~~~~~~~~~~~~~~~~~~~~

"MODULESBEGINENV" environment snapshot functionality is not supported
anymore on Modules v4. Modules collection mechanism should be used
instead to **save** and **restore** sets of enabled modulepaths and
loaded modulefiles.


Command line switches
~~~~~~~~~~~~~~~~~~~~~

Some command line switches are not supported anymore on v4.0. When
still using them, a warning message is displayed and the command is
ran with these unsupported switches ignored. Following command line
switches are concerned:

* "--force", "-f"

* "--human"

* "--verbose", "-v"

* "--silent", "-s"

* "--create", "-c"

* "--icase", "-i"

* "--userlvl" lvl, "-u" lvl


Module sub-commands
~~~~~~~~~~~~~~~~~~~

During an **help** sub-command, Modules v4 does not redirect output
made on stdout in *ModulesHelp* Tcl procedure to stderr. Moreover when
running **help**, version 4 interprets all the content of the
modulefile, then call the *ModulesHelp* procedure if it exists,
whereas Modules 3.2 only interprets the *ModulesHelp* procedure and
not the rest of the modulefile content.

When **load** is asked on an already loaded modulefiles, Modules v4
ignores this new load order whereas v3.2 refreshed shell alias
definitions found in this modulefile.

When **switching** on version 4 an *old* modulefile by a *new* one, no
error is raised if *old* modulefile is not currently loaded. In this
situation v3.2 threw an error and abort switch action. Additionally on
**switch** sub-command, *new* modulefile does not keep the position
held by *old* modulefile in loaded modules list on Modules v4 as it
was the case on v3.2. Same goes for path-like environment variables:
replaced path component is appended to the end or prepended to the
beginning of the relative path-like variable, not appended or
prepended relatively to the position hold by the swapped path
component.

During a **switch** command, version 4 interprets the swapped-out
modulefile in *unload* mode, so the sub-modulefiles loaded, with
"module load" order in the swapped-out modulefile are also unloaded
during the switch.

Modules 4 provides path element counting feature which increases a
reference counter each time a given path entry is added to a given
environment variable. This feature also applies to the "MODULEPATH"
environment variable. As consequence a modulepath entry element is
removed from the modulepath enabled list only if the related element
counter is equal to 1. When **unusing** a modulepath if its reference
counter is greater than 1, modulepath is kept enabled and reference
counter is decreased by 1.

On Modules 3.2 paths composing the "MODULEPATH" environment variable
may contain reference to environment variable. These variable
references are resolved dynamically when "MODULEPATH" is looked at
during module sub-command action. This feature has been discontinued
on Modules v4.

Following Modules sub-commands are not supported anymore on v4.0:

* "clear"

* "update"


Modules specific Tcl commands
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Modules v4 provides path element counting feature which increases a
reference counter each time a given path entry is added to a given
environment variable. As a consequence a path entry element is not
always removed from a path-like variable when calling to "remove-path"
or calling to "append-path" or "append-path" at unloading time. The
path element is removed only if its related element counter is equal
to 1. If this counter is greater than 1, path element is kept in
variable and reference counter is decreased by 1.

On Modules v4, **module-info mode** returns during an **unload** sub-
command the "unload" value instead of "remove" on Modules v3.2.
However if *mode* is tested against "remove" value, true will be
returned. During a **switch** sub-command on Modules v4, "unload" then
"load" is returned instead of "switch1" then "switch2" then "switch3"
on Modules v3.2. However if *mode* is tested against "switch" value,
true will be returned.

When using **set-alias**, Modules v3.2 defines a shell function when
variables are in use in alias value on Bourne shell derivatives,
Modules 4 always defines a shell alias never a shell function.

Some Modules specific Tcl commands are not supported anymore on v4.0.
When still using them, a warning message is displayed and these
unsupported Tcl commands are ignored. Following Modules specific Tcl
commands are concerned:

* "module-info flags"

* "module-info trace"

* "module-info tracepat"

* "module-info user"

* "module-log"

* "module-trace"

* "module-user"

* "module-verbosity"


Further reading
---------------

To get a complete list of the differences between Modules v3.2 and v4,
please read the Changes between versions document.

A significant number of issues reported for v3.2 have been closed on
v4. List of these closed issues can be found at:

https://github.com/cea-hpc/modules/milestone/1?closed=1
