Help/command/list.rst

list
----

List operations.

Synopsis
^^^^^^^^

.. parsed-literal::

  `Reading`_
    list(`LENGTH`_ <list> <out-var>)
    list(`GET`_ <list> <element index> [<index> ...] <out-var>)
    list(`JOIN`_ <list> <glue> <out-var>)
    list(`SUBLIST`_ <list> <begin> <length> <out-var>)

  `Search`_
    list(`FIND`_ <list> <value> <out-var>)

  `Modification`_
    list(`APPEND`_ <list> [<element>...])
    list(`FILTER`_ <list> {INCLUDE | EXCLUDE} REGEX <regex>)
    list(`INSERT`_ <list> <index> [<element>...])
    list(`POP_BACK`_ <list> [<out-var>...])
    list(`POP_FRONT`_ <list> [<out-var>...])
    list(`PREPEND`_ <list> [<element>...])
    list(`REMOVE_ITEM`_ <list> <value>...)
    list(`REMOVE_AT`_ <list> <index>...)
    list(`REMOVE_DUPLICATES`_ <list>)
    list(`TRANSFORM`_ <list> <ACTION> [...])

  `Ordering`_
    list(`REVERSE`_ <list>)
    list(`SORT`_ <list> [...])

Introduction
^^^^^^^^^^^^

The list subcommands ``APPEND``, ``INSERT``, ``FILTER``, ``PREPEND``,
``POP_BACK``, ``POP_FRONT``, ``REMOVE_AT``, ``REMOVE_ITEM``,
``REMOVE_DUPLICATES``, ``REVERSE`` and ``SORT`` may create
new values for the list within the current CMake variable scope.  Similar to
the :command:`set` command, the LIST command creates new variable values in
the current scope, even if the list itself is actually defined in a parent
scope.  To propagate the results of these operations upwards, use
:command:`set` with ``PARENT_SCOPE``, :command:`set` with
``CACHE INTERNAL``, or some other means of value propagation.

.. note::

  A list in cmake is a ``;`` separated group of strings.  To create a
  list the set command can be used.  For example, ``set(var a b c d e)``
  creates a list with ``a;b;c;d;e``, and ``set(var "a b c d e")`` creates a
  string or a list with one item in it.   (Note macro arguments are not
  variables, and therefore cannot be used in LIST commands.)

.. note::

  When specifying index values, if ``<element index>`` is 0 or greater, it
  is indexed from the beginning of the list, with 0 representing the
  first list element.  If ``<element index>`` is -1 or lesser, it is indexed
  from the end of the list, with -1 representing the last list element.
  Be careful when counting with negative indices: they do not start from
  0.  -0 is equivalent to 0, the first list element.

Reading
^^^^^^^

.. _LENGTH:

.. code-block:: cmake

  list(LENGTH <list> <output variable>)

Returns the list's length.

.. _GET:

.. code-block:: cmake

  list(GET <list> <element index> [<element index> ...] <output variable>)

Returns the list of elements specified by indices from the list.

.. _JOIN:

.. code-block:: cmake

  list(JOIN <list> <glue> <output variable>)

.. versionadded:: 3.12

Returns a string joining all list's elements using the glue string.
To join multiple strings, which are not part of a list, use ``JOIN`` operator
from :command:`string` command.

.. _SUBLIST:

.. code-block:: cmake

  list(SUBLIST <list> <begin> <length> <output variable>)

.. versionadded:: 3.12

Returns a sublist of the given list.
If ``<length>`` is 0, an empty list will be returned.
If ``<length>`` is -1 or the list is smaller than ``<begin>+<length>`` then
the remaining elements of the list starting at ``<begin>`` will be returned.

Search
^^^^^^

.. _FIND:

.. code-block:: cmake

  list(FIND <list> <value> <output variable>)

Returns the index of the element specified in the list or -1
if it wasn't found.

Modification
^^^^^^^^^^^^

.. _APPEND:

.. code-block:: cmake

  list(APPEND <list> [<element> ...])

Appends elements to the list. If no variable named ``<list>`` exists in the
current scope its value is treated as empty and the elements are appended to
that empty list.

.. _FILTER:

.. code-block:: cmake

  list(FILTER <list> <INCLUDE|EXCLUDE> REGEX <regular_expression>)

.. versionadded:: 3.6

Includes or removes items from the list that match the mode's pattern.
In ``REGEX`` mode, items will be matched against the given regular expression.

For more information on regular expressions look under
:ref:`string(REGEX) <Regex Specification>`.

.. _INSERT:

.. code-block:: cmake

  list(INSERT <list> <element_index> <element> [<element> ...])

Inserts elements to the list to the specified index. It is an
error to specify an out-of-range index. Valid indexes are 0 to `N`
where `N` is the length of the list, inclusive. An empty list
has length 0. If no variable named ``<list>`` exists in the
current scope its value is treated as empty and the elements are
inserted in that empty list.

.. _POP_BACK:

.. code-block:: cmake

  list(POP_BACK <list> [<out-var>...])

.. versionadded:: 3.15

If no variable name is given, removes exactly one element. Otherwise,
with `N` variable names provided, assign the last `N` elements' values
to the given variables and then remove the last `N` values from
``<list>``.

.. _POP_FRONT:

.. code-block:: cmake

  list(POP_FRONT <list> [<out-var>...])

.. versionadded:: 3.15

If no variable name is given, removes exactly one element. Otherwise,
with `N` variable names provided, assign the first `N` elements' values
to the given variables and then remove the first `N` values from
``<list>``.

.. _PREPEND:

.. code-block:: cmake

  list(PREPEND <list> [<element> ...])

.. versionadded:: 3.15

Insert elements to the 0th position in the list. If no variable named
``<list>`` exists in the current scope its value is treated as empty and
the elements are prepended to that empty list.

.. _REMOVE_ITEM:

.. code-block:: cmake

  list(REMOVE_ITEM <list> <value> [<value> ...])

Removes all instances of the given items from the list.

.. _REMOVE_AT:

.. code-block:: cmake

  list(REMOVE_AT <list> <index> [<index> ...])

Removes items at given indices from the list.

.. _REMOVE_DUPLICATES:

.. code-block:: cmake

  list(REMOVE_DUPLICATES <list>)

Removes duplicated items in the list. The relative order of items is preserved,
but if duplicates are encountered, only the first instance is preserved.

.. _TRANSFORM:

.. code-block:: cmake

  list(TRANSFORM <list> <ACTION> [<SELECTOR>]
                        [OUTPUT_VARIABLE <output variable>])

.. versionadded:: 3.12

Transforms the list by applying an action to all or, by specifying a
``<SELECTOR>``, to the selected elements of the list, storing the result
in-place or in the specified output variable.

.. note::

   The ``TRANSFORM`` sub-command does not change the number of elements in the
   list. If a ``<SELECTOR>`` is specified, only some elements will be changed,
   the other ones will remain the same as before the transformation.

``<ACTION>`` specifies the action to apply to the elements of the list.
The actions have exactly the same semantics as sub-commands of the
:command:`string` command.  ``<ACTION>`` must be one of the following:

``APPEND``, ``PREPEND``: Append, prepend specified value to each element of
the list.

  .. code-block:: cmake

    list(TRANSFORM <list> <APPEND|PREPEND> <value> ...)

``TOUPPER``, ``TOLOWER``: Convert each element of the list to upper, lower
characters.

  .. code-block:: cmake

    list(TRANSFORM <list> <TOLOWER|TOUPPER> ...)

``STRIP``: Remove leading and trailing spaces from each element of the
list.

  .. code-block:: cmake

    list(TRANSFORM <list> STRIP ...)

``GENEX_STRIP``: Strip any
:manual:`generator expressions <cmake-generator-expressions(7)>` from each
element of the list.

  .. code-block:: cmake

    list(TRANSFORM <list> GENEX_STRIP ...)

``REPLACE``: Match the regular expression as many times as possible and
substitute the replacement expression for the match for each element
of the list
(Same semantic as ``REGEX REPLACE`` from :command:`string` command).

  .. code-block:: cmake

    list(TRANSFORM <list> REPLACE <regular_expression>
                                  <replace_expression> ...)

``<SELECTOR>`` determines which elements of the list will be transformed.
Only one type of selector can be specified at a time.  When given,
``<SELECTOR>`` must be one of the following:

``AT``: Specify a list of indexes.

  .. code-block:: cmake

    list(TRANSFORM <list> <ACTION> AT <index> [<index> ...] ...)

``FOR``: Specify a range with, optionally, an increment used to iterate over
the range.

  .. code-block:: cmake

    list(TRANSFORM <list> <ACTION> FOR <start> <stop> [<step>] ...)

``REGEX``: Specify a regular expression. Only elements matching the regular
expression will be transformed.

  .. code-block:: cmake

    list(TRANSFORM <list> <ACTION> REGEX <regular_expression> ...)


Ordering
^^^^^^^^

.. _REVERSE:

.. code-block:: cmake

  list(REVERSE <list>)

Reverses the contents of the list in-place.

.. _SORT:

.. code-block:: cmake

  list(SORT <list> [COMPARE <compare>] [CASE <case>] [ORDER <order>])

Sorts the list in-place alphabetically.

.. versionadded:: 3.13
  Added the ``COMPARE``, ``CASE``, and ``ORDER`` options.

.. versionadded:: 3.18
  Added the ``COMPARE NATURAL`` option.

Use the ``COMPARE`` keyword to select the comparison method for sorting.
The ``<compare>`` option should be one of:

* ``STRING``: Sorts a list of strings alphabetically.  This is the
  default behavior if the ``COMPARE`` option is not given.
* ``FILE_BASENAME``: Sorts a list of pathnames of files by their basenames.
* ``NATURAL``: Sorts a list of strings using natural order
  (see ``strverscmp(3)`` manual), i.e. such that contiguous digits
  are compared as whole numbers.
  For example: the following list `10.0 1.1 2.1 8.0 2.0 3.1`
  will be sorted as `1.1 2.0 2.1 3.1 8.0 10.0` if the ``NATURAL``
  comparison is selected where it will be sorted as
  `1.1 10.0 2.0 2.1 3.1 8.0` with the ``STRING`` comparison.

Use the ``CASE`` keyword to select a case sensitive or case insensitive
sort mode.  The ``<case>`` option should be one of:

* ``SENSITIVE``: List items are sorted in a case-sensitive manner.  This is
  the default behavior if the ``CASE`` option is not given.
* ``INSENSITIVE``: List items are sorted case insensitively.  The order of
  items which differ only by upper/lowercase is not specified.

To control the sort order, the ``ORDER`` keyword can be given.
The ``<order>`` option should be one of:

* ``ASCENDING``: Sorts the list in ascending order.  This is the default
  behavior when the ``ORDER`` option is not given.
* ``DESCENDING``: Sorts the list in descending order.