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✏️ Editing: MIGRATING.txt

MIGRATING
*********

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.

Migrating from v4.4 to v4.5
===========================

This new version is backward-compatible with v4.4 and primarily fixes
bugs and adds new features.

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

Version 4.5 introduces new functionalities that are described in this
section.

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.

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

To get a complete list of the changes between Modules v4.4 and v4.5,
please read the Release notes document.

Migrating from v4.3 to v4.4
===========================

This new version is backward-compatible with v4.3 and primarily fixes
bugs and adds new features.

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.

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

Version 4.4 introduces new functionalities that are described in this
section.

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.

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

To get a complete list of the changes between Modules v4.3 and v4.4,
please read the Release notes document.

Migrating from v4.2 to v4.3
===========================

This new version is backward-compatible with v4.2 and primarily fixes
bugs and adds new features.

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

Version 4.3 introduces new functionalities that are described in this
section.

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.

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

To get a complete list of the changes between Modules v4.2 and v4.3,
please read the Release notes document.

Migrating from v4.1 to v4.2
===========================

This new version is backward-compatible with v4.1 and primarily fixes
bugs and adds new features.

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

Version 4.2 introduces new functionalities that are described in this
section.

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" 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 (ie. 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.

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

To get a complete list of the changes between Modules v4.1 and v4.2,
please read the Release notes document.

Migrating from v4.0 to v4.1
===========================

This new version is backward-compatible with v4.0 and primarily fixes
bugs and adds new features.

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

Version 4.1 introduces a bunch of new functionalities. These major new
features are described in this section.

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

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

To get a complete list of the changes between Modules v4.0 and v4.1,
please read the Release notes document.

Migrating from v3.2 to 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 Differences between versions 3.2 and 4 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

MR SKB