Help/command/add_custom_command.rst - master - niceSOFT/cmake

Help/command/add_custom_command.rst
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Daksh Mamodiya
Help: Clarify add_custom_command COMMENT display timing
27 июл 2026, 18:42
27 июл 2026, 18:429d9733a
add_custom_command
------------------

Add a custom build rule to the generated build system.

Synopsis
^^^^^^^^

.. parsed-literal::
  `Generating Files`_
    add_custom_command(`OUTPUT`_ <output1> [<output2> ...]
                       COMMAND <command1> [ARGS] [<args1>...]
                       [...])

  `Build Events`_
    add_custom_command(`TARGET`_ <target>
                       PRE_BUILD | PRE_LINK | POST_BUILD
                       [...])

Generating Files
^^^^^^^^^^^^^^^^

.. signature::
  add_custom_command(OUTPUT <output1> [<output2> ...]
                     COMMAND <command1> [ARGS] [<args1>...]
                     [...])

  Add a custom command to produce an output:

  .. code-block:: cmake

    add_custom_command(OUTPUT <output1> [<output2> ...]
                       COMMAND <command1> [ARGS] [<args1>...]
                       [COMMAND <command2> [ARGS] [<args2>...]] ...
                       [MAIN_DEPENDENCY depend]
                       [DEPENDS <depends>...]
                       [BYPRODUCTS <files>...]
                       [IMPLICIT_DEPENDS <lang1> <depend1>
                                        [<lang2> <depend2>] ...]
                       [WORKING_DIRECTORY <dir>]
                       [COMMENT <comment>]
                       [DEPFILE <depfile>]
                       [JOB_POOL <job_pool>]
                       [JOB_SERVER_AWARE <bool>]
                       [VERBATIM] [APPEND] [USES_TERMINAL]
                       [CODEGEN]
                       [COMMAND_EXPAND_LISTS]
                       [DEPENDS_EXPLICIT_ONLY])

  This defines a command to generate specified ``OUTPUT`` file(s).
  A target created in the same directory (``CMakeLists.txt`` file)
  that specifies any output of the custom command as a source file
  is given a rule to generate the file using the command at build time.

  Do not list the output in more than one independent target that
  may build in parallel or the instances of the rule may conflict.
  Instead, use the :command:`add_custom_target` command to drive the
  command and make the other targets depend on that one.  See the
  `Example: Generating Files for Multiple Targets`_ below.

  The options are:

  ``APPEND``
    Append the ``COMMAND`` and ``DEPENDS`` option values to the custom
    command for the first output specified.  There must have already
    been a previous call to this command with the same output.

    If the previous call specified the output via a generator expression,
    the output specified by the current call must match in at least one
    configuration after evaluating generator expressions.  In this case,
    the appended commands and dependencies apply to all configurations.

    The ``COMMENT``, ``MAIN_DEPENDENCY``, and ``WORKING_DIRECTORY``
    options are currently ignored when ``APPEND`` is given, but may be
    used in the future.

  ``BYPRODUCTS``
    .. versionadded:: 3.2

    Specify the files the command is expected to produce but whose
    modification time may or may not be newer than the dependencies.
    If a byproduct name is a relative path it will be interpreted
    relative to the build tree directory corresponding to the
    current source directory.
    Each byproduct file will be marked with the :prop_sf:`GENERATED`
    source file property automatically.

    *See policy* :policy:`CMP0058` *for the motivation behind this feature.*

    Explicit specification of byproducts is supported by the
    :generator:`Ninja` generator to tell the ``ninja`` build tool
    how to regenerate byproducts when they are missing.  It is
    also useful when other build rules (e.g. custom commands)
    depend on the byproducts.  Ninja requires a build rule for any
    generated file on which another rule depends even if there are
    order-only dependencies to ensure the byproducts will be
    available before their dependents build.

    The :ref:`Makefile Generators` will remove ``BYPRODUCTS`` and other
    :prop_sf:`GENERATED` files during ``make clean``.

    This keyword cannot be used with ``APPEND`` (see policy :policy:`CMP0175`).
    All byproducts must be set in the first call to
    ``add_custom_command(OUTPUT...)`` for the output files.

    .. versionadded:: 3.20
      Arguments to ``BYPRODUCTS`` may use a restricted set of
      :manual:`generator expressions <cmake-generator-expressions(7)>`.
      :ref:`Target-dependent expressions <Target-Dependent Expressions>`
      are not permitted.

    .. versionchanged:: 3.28
      In targets using :ref:`file sets`, custom command byproducts are now
      considered private unless they are listed in a non-private file set.
      See policy :policy:`CMP0154`.

  ``COMMAND``
    Specify the command-line(s) to execute at build time.
    At least one ``COMMAND`` would normally be given, but certain patterns
    may omit it, such as adding commands in separate calls using ``APPEND``.

    If more than one ``COMMAND`` is specified, they will be executed in order,
    but *not* necessarily composed into a stateful shell or batch script.
    To run a full script, use the :command:`configure_file` command or the
    :command:`file(GENERATE)` command to create it, and then specify
    a ``COMMAND`` to launch it.

    The optional ``ARGS`` argument is for backward compatibility and
    will be ignored.

    If ``COMMAND`` specifies an executable target name (created by the
    :command:`add_executable` command), it will automatically be replaced
    by the location of the executable created at build time if either of
    the following is true:

    * The target is not being cross-compiled (i.e. the
      :variable:`CMAKE_CROSSCOMPILING` variable is not set to true).
    * .. versionadded:: 3.6
        The target is being cross-compiled and an emulator is provided (i.e.
        its :prop_tgt:`CROSSCOMPILING_EMULATOR` target property is set).
        In this case, the contents of :prop_tgt:`CROSSCOMPILING_EMULATOR` will be
        prepended to the command before the location of the target executable.

    If neither of the above conditions are met, it is assumed that the
    command name is a program to be found on the ``PATH`` at build time.

    Arguments to ``COMMAND`` may use
    :manual:`generator expressions <cmake-generator-expressions(7)>`.
    Use the :genex:`TARGET_FILE` generator expression to refer to the location
    of a target later in the command line (i.e. as a command argument rather
    than as the command to execute).

    Whenever one of the following target based generator expressions are used as
    a command to execute or is mentioned in a command argument, a target-level
    dependency will be added automatically so that the mentioned target will be
    built before any target using this custom command
    (see policy :policy:`CMP0112`).

    * ``TARGET_FILE``
    * ``TARGET_LINKER_FILE``
    * ``TARGET_SONAME_FILE``
    * ``TARGET_PDB_FILE``

    This target-level dependency does NOT add a file-level dependency that would
    cause the custom command to re-run whenever the executable is recompiled.
    List target names with the ``DEPENDS`` option to add such file-level
    dependencies.

  ``COMMENT``
    Display the given message associated with running the commands at build
    time.  The message is passed to the native build tool, which controls when
    and how it is shown, so its exact timing relative to the commands is not
    guaranteed.  This will be ignored if ``APPEND`` is given, although a future
    version may use it.

    .. versionadded:: 3.26
      Arguments to ``COMMENT`` may use
      :manual:`generator expressions <cmake-generator-expressions(7)>`.

  ``DEPENDS``
    Specify files on which the command depends.  Each argument is converted
    to a dependency as follows:

    1. If the argument is the name of a target (created by the
       :command:`add_custom_target`, :command:`add_executable`, or
       :command:`add_library` command) a target-level dependency is
       created to make sure the target is built before any target
       using this custom command.  Additionally, if the target is an
       executable or library, a file-level dependency is created to
       cause the custom command to re-run whenever the target is
       recompiled.

       .. versionchanged:: 4.4

         Previously an executable target could be specified using the name
         of the target with ``.exe`` appended.  This is no longer allowed.
         See policy :policy:`CMP0212`.

    2. If the argument is an absolute path, a file-level dependency
       is created on that path.

    3. If the argument is the name of a source file that has been
       added to a target or on which a source file property has been set,
       a file-level dependency is created on that source file.

    4. If the argument is a relative path and it exists in the current
       source directory, a file-level dependency is created on that
       file in the current source directory.

    5. Otherwise, a file-level dependency is created on that path relative
       to the current binary directory.

    If any dependency is an ``OUTPUT`` of another custom command in the same
    directory (``CMakeLists.txt`` file), CMake automatically brings the other
    custom command into the target in which this command is built.

    .. versionadded:: 3.16
      A target-level dependency is added if any dependency is listed as
      ``BYPRODUCTS`` of a target or any of its build events in the same
      directory to ensure the byproducts will be available.

    If ``DEPENDS`` is not specified, the command will run whenever
    the ``OUTPUT`` is missing; if the command does not actually
    create the ``OUTPUT``, the rule will always run.

    .. versionadded:: 3.1
      Arguments to ``DEPENDS`` may use
      :manual:`generator expressions <cmake-generator-expressions(7)>`.

  ``COMMAND_EXPAND_LISTS``
    .. versionadded:: 3.8

    Lists in ``COMMAND`` arguments will be expanded, including those
    created with
    :manual:`generator expressions <cmake-generator-expressions(7)>`,
    allowing ``COMMAND`` arguments such as
    ``${CC} "-I$<JOIN:$<TARGET_PROPERTY:foo,INCLUDE_DIRECTORIES>,;-I>" foo.cc``
    to be properly expanded.

    This keyword cannot be used with ``APPEND`` (see policy :policy:`CMP0175`).
    If the appended commands need this option to be set, it must be set on the
    first call to ``add_custom_command(OUTPUT...)`` for the output files.

  ``CODEGEN``
    .. versionadded:: 3.31

    Adds the custom command to a global ``codegen`` target that can be
    used to execute the custom command while avoiding the majority of the
    build graph.

    This option is supported only by :ref:`Ninja Generators` and
    :ref:`Makefile Generators`, and is ignored by other generators.
    Furthermore, this option is allowed only if policy :policy:`CMP0171`
    is set to ``NEW``.

    This keyword cannot be used with ``APPEND`` (see policy :policy:`CMP0175`).
    It can only be set on the first call to ``add_custom_command(OUTPUT...)``
    for the output files.

  ``IMPLICIT_DEPENDS``
    Request scanning of implicit dependencies of an input file.
    The language given specifies the programming language whose
    corresponding dependency scanner should be used.
    Currently only ``C`` and ``CXX`` language scanners are supported.
    The language has to be specified for every file in the
    ``IMPLICIT_DEPENDS`` list.  Dependencies discovered from the
    scanning are added to those of the custom command at build time.
    Note that the ``IMPLICIT_DEPENDS`` option is currently supported
    only for Makefile generators and will be ignored by other generators.

    .. note::

      This option cannot be specified at the same time as ``DEPFILE`` option.

  ``JOB_POOL``
    .. versionadded:: 3.15

    Specify a :prop_gbl:`pool <JOB_POOLS>` for the :generator:`Ninja`
    generator. Incompatible with ``USES_TERMINAL``, which implies
    the ``console`` pool.
    Using a pool that is not defined by :prop_gbl:`JOB_POOLS` causes
    an error by ninja at build time.

    This keyword cannot be used with ``APPEND`` (see policy :policy:`CMP0175`).
    Job pools can only be specified in the first call to
    ``add_custom_command(OUTPUT...)`` for the output files.

  ``JOB_SERVER_AWARE``
    .. versionadded:: 3.28

    Specify that the command is GNU Make job server aware.

    For the :generator:`Unix Makefiles`, :generator:`MSYS Makefiles`, and
    :generator:`MinGW Makefiles` generators this will add the ``+`` prefix to the
    recipe line. See the `GNU Make Documentation`_ for more information.

    This option is silently ignored by other generators.

    This keyword cannot be used with ``APPEND`` (see policy :policy:`CMP0175`).
    Job server awareness can only be specified in the first call to
    ``add_custom_command(OUTPUT...)`` for the output files.

  .. _`GNU Make Documentation`: https://www.gnu.org/software/make/manual/html_node/MAKE-Variable.html

  ``MAIN_DEPENDENCY``
    Specify the primary input source file to the command.  This is
    treated just like any value given to the ``DEPENDS`` option
    but also suggests to :ref:`Visual Studio Generators` where to hang
    the custom command. Each source file may have at most one command
    specifying it as its main dependency. A compile command (i.e. for a
    library or an executable) counts as an implicit main dependency which
    gets silently overwritten by a custom command specification.

    This option is currently ignored if ``APPEND`` is given, but a future
    version may use it.

  ``OUTPUT``
    Specify the output files the command is expected to produce.
    Each output file will be marked with the :prop_sf:`GENERATED`
    source file property automatically.
    If the output of the custom command is not actually created
    as a file on disk it should be marked with the :prop_sf:`SYMBOLIC`
    source file property.

    If an output file name is a relative path, its absolute path is
    determined by interpreting it relative to:

    1. the build directory corresponding to the current source directory
       (:variable:`CMAKE_CURRENT_BINARY_DIR`), or

    2. the current source directory (:variable:`CMAKE_CURRENT_SOURCE_DIR`).

    The path in the build directory is preferred unless the path in the
    source tree is mentioned as an absolute source file path elsewhere
    in the current directory.

    The output file path may not contain ``<`` or ``>`` characters.

    .. versionadded:: 3.20
      Arguments to ``OUTPUT`` may use a restricted set of
      :manual:`generator expressions <cmake-generator-expressions(7)>`.
      :ref:`Target-dependent expressions <Target-Dependent Expressions>`
      are not permitted.

    .. versionchanged:: 3.28
      In targets using :ref:`file sets`, custom command outputs are now
      considered private unless they are listed in a non-private file set.
      See policy :policy:`CMP0154`.

    .. versionchanged:: 3.30
      The output file path may now use ``#`` characters, except
      when using the :generator:`Borland Makefiles` generator.

  ``USES_TERMINAL``
    .. versionadded:: 3.2

    The command will be given direct access to the terminal if possible.
    With the :generator:`Ninja` generator, this places the command in
    the ``console`` :prop_gbl:`pool <JOB_POOLS>`.

    This keyword cannot be used with ``APPEND`` (see policy :policy:`CMP0175`).
    If the appended commands need access to the terminal, it must be set on
    the first call to ``add_custom_command(OUTPUT...)`` for the output files.

  ``VERBATIM``
    All arguments to the commands will be escaped properly for the
    build tool so that the invoked command receives each argument
    unchanged.  Note that one level of escapes is still used by the
    CMake language processor before add_custom_command even sees the
    arguments.  Use of ``VERBATIM`` is recommended as it enables
    correct behavior.  When ``VERBATIM`` is not given the behavior
    is platform specific because there is no protection of
    tool-specific special characters.

    This keyword cannot be used with ``APPEND`` (see policy :policy:`CMP0175`).
    If the appended commands need to be treated as ``VERBATIM``, it must be set
    on the first call to ``add_custom_command(OUTPUT...)`` for the output files.

  ``WORKING_DIRECTORY``
    Execute the command with the given current working directory.
    If it is a relative path, it will be interpreted relative to the
    build tree directory corresponding to the current source directory.
    If not specified, set to :variable:`CMAKE_CURRENT_BINARY_DIR`.

    This option is currently ignored if ``APPEND`` is given, but a future
    version may use it.

    .. versionadded:: 3.13
      Arguments to ``WORKING_DIRECTORY`` may use
      :manual:`generator expressions <cmake-generator-expressions(7)>`.

  ``DEPFILE``
    .. versionadded:: 3.7

    Specify a depfile which holds dependencies for the custom command. It is
    usually emitted by the custom command itself.  This keyword may only be used
    if the generator supports it, as detailed below.

    The expected format, compatible with what is generated by ``gcc`` with the
    option ``-M``, is independent of the generator or platform.

    The formal syntax, as specified using
    `BNF <https://en.wikipedia.org/wiki/Backus%E2%80%93Naur_form>`_ notation with
    the regular extensions, is the following:

    .. raw:: latex

      \begin{small}

    .. productionlist:: depfile
      depfile: `rule`*
      rule: `targets` (':' (`separator` `dependencies`?)?)? `eol`
      targets: `target` (`separator` `target`)* `separator`*
      target: `pathname`
      dependencies: `dependency` (`separator` `dependency`)* `separator`*
      dependency: `pathname`
      separator: (`space` | `line_continue`)+
      line_continue: '\' `eol`
      space: ' ' | '\t'
      pathname: `character`+
      character: `std_character` | `dollar` | `hash` | `whitespace`
      std_character: <any character except '$', '#' or ' '>
      dollar: '$$'
      hash: '\#'
      whitespace: '\ '
      eol: '\r'? '\n'

    .. raw:: latex

      \end{small}

    .. note::

      As part of ``pathname``, any slash and backslash is interpreted as
      a directory separator.

    .. versionadded:: 3.7
      The :generator:`Ninja` generator supports ``DEPFILE`` since the keyword
      was first added.

    .. versionadded:: 3.17
      Added the :generator:`Ninja Multi-Config` generator, which included
      support for the ``DEPFILE`` keyword.

    .. versionadded:: 3.20
      Added support for :ref:`Makefile Generators`.

      .. note::

        ``DEPFILE`` cannot be specified at the same time as the
        ``IMPLICIT_DEPENDS`` option for :ref:`Makefile Generators`.

    .. versionadded:: 3.21
      Added support for :ref:`Visual Studio Generators` with VS 2012 and above,
      and for the :generator:`Xcode` generator.  Support for
      :manual:`generator expressions <cmake-generator-expressions(7)>` was also
      added.

    .. versionadded:: 3.29
      The :ref:`Ninja Generators` will now incorporate the dependencies into its
      "deps log" database if the file is not listed in ``OUTPUTS`` or
      ``BYPRODUCTS``.

    Using ``DEPFILE`` with generators other than those listed above is an error.

    If the ``DEPFILE`` argument is relative, it should be relative to
    :variable:`CMAKE_CURRENT_BINARY_DIR`, and any relative paths inside the
    ``DEPFILE`` should also be relative to :variable:`CMAKE_CURRENT_BINARY_DIR`.
    See policy :policy:`CMP0116`, which is always ``NEW`` for
    :ref:`Makefile Generators`, :ref:`Visual Studio Generators`,
    and the :generator:`Xcode` generator.

    This keyword cannot be used with ``APPEND`` (see policy :policy:`CMP0175`).
    Depfiles can only be set on the first call to
    ``add_custom_command(OUTPUT...)`` for the output files.

  ``DEPENDS_EXPLICIT_ONLY``

    .. versionadded:: 3.27

    Indicates that the command's ``DEPENDS`` argument represents all files
    required by the command and implicit dependencies are not required.

    Without this option, if any target uses the output of the custom command,
    CMake will consider that target's dependencies as implicit dependencies for
    the custom command in case this custom command requires files implicitly
    created by those targets.

    This option can be enabled on all custom commands by setting
    :variable:`CMAKE_ADD_CUSTOM_COMMAND_DEPENDS_EXPLICIT_ONLY` to ``ON``.

    This keyword cannot be used with ``APPEND`` (see policy :policy:`CMP0175`).
    It can only be set on the first call to ``add_custom_command(OUTPUT...)``
    for the output files.

    Only the :ref:`Ninja Generators` actually use this information to remove
    unnecessary implicit dependencies.

    See also the :prop_tgt:`OPTIMIZE_DEPENDENCIES` target property, which may
    provide another way for reducing the impact of target dependencies in some
    scenarios.

Examples: Generating Files
^^^^^^^^^^^^^^^^^^^^^^^^^^

Custom commands may be used to generate source files.
For example, the code:

.. code-block:: cmake

  add_custom_command(
    OUTPUT out.c
    COMMAND someTool -i ${CMAKE_CURRENT_SOURCE_DIR}/in.txt
                     -o out.c
    DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/in.txt
    VERBATIM)
  add_library(myLib out.c)

adds a custom command to run ``someTool`` to generate ``out.c`` and then
compile the generated source as part of a library.  The generation rule
will re-run whenever ``in.txt`` changes.

.. versionadded:: 3.20
  One may use generator expressions to specify per-configuration outputs.
  For example, the code:

  .. code-block:: cmake

    add_custom_command(
      OUTPUT "out-$<CONFIG>.c"
      COMMAND someTool -i ${CMAKE_CURRENT_SOURCE_DIR}/in.txt
                       -o "out-$<CONFIG>.c"
                       -c "$<CONFIG>"
      DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/in.txt
      VERBATIM)
    add_library(myLib "out-$<CONFIG>.c")

  adds a custom command to run ``someTool`` to generate ``out-<config>.c``,
  where ``<config>`` is the build configuration, and then compile the generated
  source as part of a library.

.. versionadded:: 3.31
  Use the ``CODEGEN`` option to add a custom command's outputs to the builtin
  ``codegen`` target.  This is useful to make generated code available for
   static analysis without building the entire project.  For example:

  .. code-block:: cmake

    add_executable(someTool someTool.c)

    add_custom_command(
      OUTPUT out.c
      COMMAND someTool -o out.c
      CODEGEN)

    add_library(myLib out.c)

  A user may build the ``codegen`` target to generate ``out.c``.
  ``someTool`` is built as dependency, but ``myLib`` is not built at all.

Example: Generating Files for Multiple Targets
""""""""""""""""""""""""""""""""""""""""""""""

If multiple independent targets need the same custom command output,
it must be attached to a single custom target on which they all depend.
Consider the following example:

.. code-block:: cmake

  add_custom_command(
    OUTPUT table.csv
    COMMAND makeTable -i ${CMAKE_CURRENT_SOURCE_DIR}/input.dat
                      -o table.csv
    DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/input.dat
    VERBATIM)
  add_custom_target(generate_table_csv DEPENDS table.csv)

  add_custom_command(
    OUTPUT foo.cxx
    COMMAND genFromTable -i table.csv -case foo -o foo.cxx
    DEPENDS table.csv           # file-level dependency
            generate_table_csv  # target-level dependency
    VERBATIM)
  add_library(foo foo.cxx)

  add_custom_command(
    OUTPUT bar.cxx
    COMMAND genFromTable -i table.csv -case bar -o bar.cxx
    DEPENDS table.csv           # file-level dependency
            generate_table_csv  # target-level dependency
    VERBATIM)
  add_library(bar bar.cxx)

Output ``foo.cxx`` is needed only by target ``foo`` and output ``bar.cxx``
is needed only by target ``bar``, but *both* targets need ``table.csv``,
transitively.  Since ``foo`` and ``bar`` are independent targets that may
build concurrently, we prevent them from racing to generate ``table.csv``
by placing its custom command in a separate target, ``generate_table_csv``.
The custom commands generating ``foo.cxx`` and ``bar.cxx`` each specify a
target-level dependency on ``generate_table_csv``, so the targets using them,
``foo`` and ``bar``, will not build until after target ``generate_table_csv``
is built.

Build Events
^^^^^^^^^^^^

.. signature::
  add_custom_command(TARGET <target>
                     PRE_BUILD | PRE_LINK | POST_BUILD
                     [...])

  Add a build event to a target such as a
  library or executable.  This is useful for performing an operation
  before or after building the target.  The command becomes part of the
  target and will only execute when the target itself is built.  If the
  target is already built, the command will not execute.

  .. code-block:: cmake

    add_custom_command(TARGET <target>
                       PRE_BUILD | PRE_LINK | POST_BUILD
                       COMMAND <command1> [ARGS] [<args1>...]
                       [COMMAND <command2> [ARGS] [<args2>...]] ...
                       [BYPRODUCTS <files>...]
                       [WORKING_DIRECTORY <dir>]
                       [COMMENT <comment>]
                       [VERBATIM]
                       [COMMAND_EXPAND_LISTS]
                       [USES_TERMINAL])

  This defines a new command that will be associated with building the
  specified ``<target>``.  The ``<target>`` must be defined in the current
  directory; targets defined in other directories may not be specified.

  When the command will happen is determined by which
  of the following is specified:

  ``PRE_BUILD``
    This option has unique behavior for the :ref:`Visual Studio Generators`.
    When using one of the Visual Studio generators, the command will run before
    any other rules are executed within the target.  With all other generators,
    this option behaves the same as ``PRE_LINK`` instead.  Because of this,
    it is recommended to avoid using ``PRE_BUILD`` except when it is known that
    a Visual Studio generator is being used.
  ``PRE_LINK``
    Run after sources have been compiled but before linking the binary
    or running the librarian or archiver tool of a static library.
    This is not defined for targets created by the
    :command:`add_custom_target` command.
  ``POST_BUILD``
    Run after all other rules within the target have been executed.

  Projects should always specify one of the above three keywords when using
  the ``TARGET`` form.  See policy :policy:`CMP0175`.

  All other keywords shown in the signature above have the same meaning as they
  do for the :command:`add_custom_command(OUTPUT)` form of the command.
  At least one ``COMMAND`` must be given, see policy :policy:`CMP0175`.

.. note::
  Because generator expressions can be used in custom commands,
  it is possible to define ``COMMAND`` lines or whole custom commands
  which evaluate to empty strings for certain configurations.
  For :ref:`Visual Studio Generators` these command
  lines or custom commands will be omitted for the specific
  configuration and no "empty-string-command" will be added.

  This allows adding individual build events for every configuration.

.. versionadded:: 3.21
  Support for target-dependent generator expressions.

.. versionadded:: 3.29
  The ``<target>`` may be an :ref:`ALIAS target <Alias Targets>`.

Examples: Build Events
^^^^^^^^^^^^^^^^^^^^^^

A ``POST_BUILD`` event may be used to post-process a binary after linking.
For example, the code:

.. code-block:: cmake

  add_executable(myExe myExe.c)
  add_custom_command(
    TARGET myExe POST_BUILD
    COMMAND someHasher -i "$<TARGET_FILE:myExe>"
                       -o "$<TARGET_FILE:myExe>.hash"
    VERBATIM)

will run ``someHasher`` to produce a ``.hash`` file next to the executable
after linking.

.. versionadded:: 3.20
  One may use generator expressions to specify per-configuration byproducts.
  For example, the code:

  .. code-block:: cmake

    add_library(myPlugin MODULE myPlugin.c)
    add_custom_command(
      TARGET myPlugin POST_BUILD
      COMMAND someHasher -i "$<TARGET_FILE:myPlugin>"
                         --as-code "myPlugin-hash-$<CONFIG>.c"
      BYPRODUCTS "myPlugin-hash-$<CONFIG>.c"
      VERBATIM)
    add_executable(myExe myExe.c "myPlugin-hash-$<CONFIG>.c")

  will run ``someHasher`` after linking ``myPlugin``, e.g. to produce a ``.c``
  file containing code to check the hash of ``myPlugin`` that the ``myExe``
  executable can use to verify it before loading.

Ninja Multi-Config
^^^^^^^^^^^^^^^^^^

.. versionadded:: 3.20

  ``add_custom_command`` supports the :generator:`Ninja Multi-Config`
  generator's cross-config capabilities. See the generator documentation
  for more information.

See Also
^^^^^^^^

* :command:`add_custom_target`