CMake/Help/command/file.rst

file
----

File manipulation command.

Synopsis
^^^^^^^^

.. parsed-literal::

  `Reading`_
    file(`READ`_ <filename> <out-var> [...])
    file(`STRINGS`_ <filename> <out-var> [...])
    file(`\<HASH\> <HASH_>`_ <filename> <out-var>)
    file(`TIMESTAMP`_ <filename> <out-var> [...])

  `Writing`_
    file({`WRITE`_ | `APPEND`_} <filename> <content>...)
    file({`TOUCH`_ | `TOUCH_NOCREATE`_} [<file>...])
    file(`GENERATE`_ OUTPUT <output-file> [...])

  `Filesystem`_
    file({`GLOB`_ | `GLOB_RECURSE`_} <out-var> [...] [<globbing-expr>...])
    file(`RENAME`_ <oldname> <newname>)
    file({`REMOVE`_ | `REMOVE_RECURSE`_ } [<files>...])
    file(`MAKE_DIRECTORY`_ [<dir>...])
    file({`COPY`_ | `INSTALL`_} <file>... DESTINATION <dir> [...])
    file(`SIZE`_ <filename> <out-var>)
    file(`READ_SYMLINK`_ <linkname> <out-var>)
    file(`CREATE_LINK`_ <original> <linkname> [...])

  `Path Conversion`_
    file(`RELATIVE_PATH`_ <out-var> <directory> <file>)
    file({`TO_CMAKE_PATH`_ | `TO_NATIVE_PATH`_} <path> <out-var>)

  `Transfer`_
    file(`DOWNLOAD`_ <url> <file> [...])
    file(`UPLOAD`_ <file> <url> [...])

  `Locking`_
    file(`LOCK`_ <path> [...])

Reading
^^^^^^^

.. _READ:

.. code-block:: cmake

  file(READ <filename> <variable>
       [OFFSET <offset>] [LIMIT <max-in>] [HEX])

Read content from a file called ``<filename>`` and store it in a
``<variable>``.  Optionally start from the given ``<offset>`` and
read at most ``<max-in>`` bytes.  The ``HEX`` option causes data to
be converted to a hexadecimal representation (useful for binary data).

.. _STRINGS:

.. code-block:: cmake

  file(STRINGS <filename> <variable> [<options>...])

Parse a list of ASCII strings from ``<filename>`` and store it in
``<variable>``.  Binary data in the file are ignored.  Carriage return
(``\r``, CR) characters are ignored.  The options are:

``LENGTH_MAXIMUM <max-len>``
 Consider only strings of at most a given length.

``LENGTH_MINIMUM <min-len>``
 Consider only strings of at least a given length.

``LIMIT_COUNT <max-num>``
 Limit the number of distinct strings to be extracted.

``LIMIT_INPUT <max-in>``
 Limit the number of input bytes to read from the file.

``LIMIT_OUTPUT <max-out>``
 Limit the number of total bytes to store in the ``<variable>``.

``NEWLINE_CONSUME``
 Treat newline characters (``\n``, LF) as part of string content
 instead of terminating at them.

``NO_HEX_CONVERSION``
 Intel Hex and Motorola S-record files are automatically converted to
 binary while reading unless this option is given.

``REGEX <regex>``
 Consider only strings that match the given regular expression.

``ENCODING <encoding-type>``
 Consider strings of a given encoding.  Currently supported encodings are:
 UTF-8, UTF-16LE, UTF-16BE, UTF-32LE, UTF-32BE.  If the ENCODING option
 is not provided and the file has a Byte Order Mark, the ENCODING option
 will be defaulted to respect the Byte Order Mark.

For example, the code

.. code-block:: cmake

  file(STRINGS myfile.txt myfile)

stores a list in the variable ``myfile`` in which each item is a line
from the input file.

.. _HASH:

.. code-block:: cmake

  file(<HASH> <filename> <variable>)

Compute a cryptographic hash of the content of ``<filename>`` and
store it in a ``<variable>``.  The supported ``<HASH>`` algorithm names
are those listed by the :ref:`string(\<HASH\>) <Supported Hash Algorithms>`
command.

.. _TIMESTAMP:

.. code-block:: cmake

  file(TIMESTAMP <filename> <variable> [<format>] [UTC])

Compute a string representation of the modification time of ``<filename>``
and store it in ``<variable>``.  Should the command be unable to obtain a
timestamp variable will be set to the empty string ("").

See the :command:`string(TIMESTAMP)` command for documentation of
the ``<format>`` and ``UTC`` options.

Writing
^^^^^^^

.. _WRITE:
.. _APPEND:

.. code-block:: cmake

  file(WRITE <filename> <content>...)
  file(APPEND <filename> <content>...)

Write ``<content>`` into a file called ``<filename>``.  If the file does
not exist, it will be created.  If the file already exists, ``WRITE``
mode will overwrite it and ``APPEND`` mode will append to the end.
Any directories in the path specified by ``<filename>`` that do not
exist will be created.

If the file is a build input, use the :command:`configure_file` command
to update the file only when its content changes.

.. _TOUCH:
.. _TOUCH_NOCREATE:

.. code-block:: cmake

  file(TOUCH [<files>...])
  file(TOUCH_NOCREATE [<files>...])

Create a file with no content if it does not yet exist. If the file already
exists, its access and/or modification will be updated to the time when the
function call is executed.

Use TOUCH_NOCREATE to touch a file if it exists but not create it. If a file
does not exist it will be silently ignored.

With TOUCH and TOUCH_NOCREATE the contents of an existing file will not be
modified.

.. _GENERATE:

.. code-block:: cmake

  file(GENERATE OUTPUT output-file
       <INPUT input-file|CONTENT content>
       [CONDITION expression])

Generate an output file for each build configuration supported by the current
:manual:`CMake Generator <cmake-generators(7)>`.  Evaluate
:manual:`generator expressions <cmake-generator-expressions(7)>`
from the input content to produce the output content.  The options are:

``CONDITION <condition>``
  Generate the output file for a particular configuration only if
  the condition is true.  The condition must be either ``0`` or ``1``
  after evaluating generator expressions.

``CONTENT <content>``
  Use the content given explicitly as input.

``INPUT <input-file>``
  Use the content from a given file as input.
  A relative path is treated with respect to the value of
  :variable:`CMAKE_CURRENT_SOURCE_DIR`.  See policy :policy:`CMP0070`.

``OUTPUT <output-file>``
  Specify the output file name to generate.  Use generator expressions
  such as ``$<CONFIG>`` to specify a configuration-specific output file
  name.  Multiple configurations may generate the same output file only
  if the generated content is identical.  Otherwise, the ``<output-file>``
  must evaluate to an unique name for each configuration.
  A relative path (after evaluating generator expressions) is treated
  with respect to the value of :variable:`CMAKE_CURRENT_BINARY_DIR`.
  See policy :policy:`CMP0070`.

Exactly one ``CONTENT`` or ``INPUT`` option must be given.  A specific
``OUTPUT`` file may be named by at most one invocation of ``file(GENERATE)``.
Generated files are modified and their timestamp updated on subsequent cmake
runs only if their content is changed.

Note also that ``file(GENERATE)`` does not create the output file until the
generation phase. The output file will not yet have been written when the
``file(GENERATE)`` command returns, it is written only after processing all
of a project's ``CMakeLists.txt`` files.

Filesystem
^^^^^^^^^^

.. _GLOB:
.. _GLOB_RECURSE:

.. code-block:: cmake

  file(GLOB <variable>
       [LIST_DIRECTORIES true|false] [RELATIVE <path>] [CONFIGURE_DEPENDS]
       [<globbing-expressions>...])
  file(GLOB_RECURSE <variable> [FOLLOW_SYMLINKS]
       [LIST_DIRECTORIES true|false] [RELATIVE <path>] [CONFIGURE_DEPENDS]
       [<globbing-expressions>...])

Generate a list of files that match the ``<globbing-expressions>`` and
store it into the ``<variable>``.  Globbing expressions are similar to
regular expressions, but much simpler.  If ``RELATIVE`` flag is
specified, the results will be returned as relative paths to the given
path.  The results will be ordered lexicographically.

If the ``CONFIGURE_DEPENDS`` flag is specified, CMake will add logic
to the main build system check target to rerun the flagged ``GLOB`` commands
at build time. If any of the outputs change, CMake will regenerate the build
system.

By default ``GLOB`` lists directories - directories are omitted in result if
``LIST_DIRECTORIES`` is set to false.

.. note::
  We do not recommend using GLOB to collect a list of source files from
  your source tree.  If no CMakeLists.txt file changes when a source is
  added or removed then the generated build system cannot know when to
  ask CMake to regenerate.
  The ``CONFIGURE_DEPENDS`` flag may not work reliably on all generators, or if
  a new generator is added in the future that cannot support it, projects using
  it will be stuck. Even if ``CONFIGURE_DEPENDS`` works reliably, there is
  still a cost to perform the check on every rebuild.

Examples of globbing expressions include::

  *.cxx      - match all files with extension cxx
  *.vt?      - match all files with extension vta,...,vtz
  f[3-5].txt - match files f3.txt, f4.txt, f5.txt

The ``GLOB_RECURSE`` mode will traverse all the subdirectories of the
matched directory and match the files.  Subdirectories that are symlinks
are only traversed if ``FOLLOW_SYMLINKS`` is given or policy
:policy:`CMP0009` is not set to ``NEW``.

By default ``GLOB_RECURSE`` omits directories from result list - setting
``LIST_DIRECTORIES`` to true adds directories to result list.
If ``FOLLOW_SYMLINKS`` is given or policy :policy:`CMP0009` is not set to
``OLD`` then ``LIST_DIRECTORIES`` treats symlinks as directories.

Examples of recursive globbing include::

  /dir/*.py  - match all python files in /dir and subdirectories

.. _RENAME:

.. code-block:: cmake

  file(RENAME <oldname> <newname>)

Move a file or directory within a filesystem from ``<oldname>`` to
``<newname>``, replacing the destination atomically.

.. _REMOVE:
.. _REMOVE_RECURSE:

.. code-block:: cmake

  file(REMOVE [<files>...])
  file(REMOVE_RECURSE [<files>...])

Remove the given files.  The ``REMOVE_RECURSE`` mode will remove the given
files and directories, also non-empty directories. No error is emitted if a
given file does not exist.

.. _MAKE_DIRECTORY:

.. code-block:: cmake

  file(MAKE_DIRECTORY [<directories>...])

Create the given directories and their parents as needed.

.. _COPY:
.. _INSTALL:

.. code-block:: cmake

  file(<COPY|INSTALL> <files>... DESTINATION <dir>
       [FILE_PERMISSIONS <permissions>...]
       [DIRECTORY_PERMISSIONS <permissions>...]
       [NO_SOURCE_PERMISSIONS] [USE_SOURCE_PERMISSIONS]
       [FILES_MATCHING]
       [[PATTERN <pattern> | REGEX <regex>]
        [EXCLUDE] [PERMISSIONS <permissions>...]] [...])

The ``COPY`` signature copies files, directories, and symlinks to a
destination folder.  Relative input paths are evaluated with respect
to the current source directory, and a relative destination is
evaluated with respect to the current build directory.  Copying
preserves input file timestamps, and optimizes out a file if it exists
at the destination with the same timestamp.  Copying preserves input
permissions unless explicit permissions or ``NO_SOURCE_PERMISSIONS``
are given (default is ``USE_SOURCE_PERMISSIONS``).

See the :command:`install(DIRECTORY)` command for documentation of
permissions, ``FILES_MATCHING``, ``PATTERN``, ``REGEX``, and
``EXCLUDE`` options.  Copying directories preserves the structure
of their content even if options are used to select a subset of
files.

The ``INSTALL`` signature differs slightly from ``COPY``: it prints
status messages (subject to the :variable:`CMAKE_INSTALL_MESSAGE` variable),
and ``NO_SOURCE_PERMISSIONS`` is default.
Installation scripts generated by the :command:`install` command
use this signature (with some undocumented options for internal use).

.. _SIZE:

.. code-block:: cmake

  file(SIZE <filename> <variable>)

Determine the file size of the ``<filename>`` and put the result in
``<variable>`` variable. Requires that ``<filename>`` is a valid path
pointing to a file and is readable.

.. _READ_SYMLINK:

.. code-block:: cmake

  file(READ_SYMLINK <linkname> <variable>)

This subcommand queries the symlink ``<linkname>`` and stores the path it
points to in the result ``<variable>``.  If ``<linkname>`` does not exist or
is not a symlink, CMake issues a fatal error.

Note that this command returns the raw symlink path and does not resolve
a relative path.  The following is an example of how to ensure that an
absolute path is obtained:

.. code-block:: cmake

  set(linkname "/path/to/foo.sym")
  file(READ_SYMLINK "${linkname}" result)
  if(NOT IS_ABSOLUTE "${result}")
    get_filename_component(dir "${linkname}" DIRECTORY)
    set(result "${dir}/${result}")
  endif()

.. _CREATE_LINK:

.. code-block:: cmake

  file(CREATE_LINK <original> <linkname>
       [RESULT <result>] [COPY_ON_ERROR] [SYMBOLIC])

Create a link ``<linkname>`` that points to ``<original>``.
It will be a hard link by default, but providing the ``SYMBOLIC`` option
results in a symbolic link instead.  Hard links require that ``original``
exists and is a file, not a directory.  If ``<linkname>`` already exists,
it will be overwritten.

The ``<result>`` variable, if specified, receives the status of the operation.
It is set to ``0`` upon success or an error message otherwise.  If ``RESULT``
is not specified and the operation fails, a fatal error is emitted.

Specifying ``COPY_ON_ERROR`` enables copying the file as a fallback if
creating the link fails.  It can be useful for handling situations such as
``<original>`` and ``<linkname>`` being on different drives or mount points,
which would make them unable to support a hard link.

Path Conversion
^^^^^^^^^^^^^^^

.. _RELATIVE_PATH:

.. code-block:: cmake

  file(RELATIVE_PATH <variable> <directory> <file>)

Compute the relative path from a ``<directory>`` to a ``<file>`` and
store it in the ``<variable>``.

.. _TO_CMAKE_PATH:
.. _TO_NATIVE_PATH:

.. code-block:: cmake

  file(TO_CMAKE_PATH "<path>" <variable>)
  file(TO_NATIVE_PATH "<path>" <variable>)

The ``TO_CMAKE_PATH`` mode converts a native ``<path>`` into a cmake-style
path with forward-slashes (``/``).  The input can be a single path or a
system search path like ``$ENV{PATH}``.  A search path will be converted
to a cmake-style list separated by ``;`` characters.

The ``TO_NATIVE_PATH`` mode converts a cmake-style ``<path>`` into a native
path with platform-specific slashes (``\`` on Windows and ``/`` elsewhere).

Always use double quotes around the ``<path>`` to be sure it is treated
as a single argument to this command.

Transfer
^^^^^^^^

.. _DOWNLOAD:
.. _UPLOAD:

.. code-block:: cmake

  file(DOWNLOAD <url> <file> [<options>...])
  file(UPLOAD   <file> <url> [<options>...])

The ``DOWNLOAD`` mode downloads the given ``<url>`` to a local ``<file>``.
The ``UPLOAD`` mode uploads a local ``<file>`` to a given ``<url>``.

Options to both ``DOWNLOAD`` and ``UPLOAD`` are:

``INACTIVITY_TIMEOUT <seconds>``
  Terminate the operation after a period of inactivity.

``LOG <variable>``
  Store a human-readable log of the operation in a variable.

``SHOW_PROGRESS``
  Print progress information as status messages until the operation is
  complete.

``STATUS <variable>``
  Store the resulting status of the operation in a variable.
  The status is a ``;`` separated list of length 2.
  The first element is the numeric return value for the operation,
  and the second element is a string value for the error.
  A ``0`` numeric error means no error in the operation.

``TIMEOUT <seconds>``
  Terminate the operation after a given total time has elapsed.

``USERPWD <username>:<password>``
  Set username and password for operation.

``HTTPHEADER <HTTP-header>``
  HTTP header for operation. Suboption can be repeated several times.

``NETRC <level>``
  Specify whether the .netrc file is to be used for operation.  If this
  option is not specified, the value of the ``CMAKE_NETRC`` variable
  will be used instead.
  Valid levels are:

  ``IGNORED``
    The .netrc file is ignored.
    This is the default.
  ``OPTIONAL``
    The .netrc file is optional, and information in the URL is preferred.
    The file will be scanned to find which ever information is not specified
    in the URL.
  ``REQUIRED``
    The .netrc file is required, and information in the URL is ignored.

``NETRC_FILE <file>``
  Specify an alternative .netrc file to the one in your home directory,
  if the ``NETRC`` level is ``OPTIONAL`` or ``REQUIRED``. If this option
  is not specified, the value of the ``CMAKE_NETRC_FILE`` variable will
  be used instead.

If neither ``NETRC`` option is given CMake will check variables
``CMAKE_NETRC`` and ``CMAKE_NETRC_FILE``, respectively.

Additional options to ``DOWNLOAD`` are:

``EXPECTED_HASH ALGO=<value>``

  Verify that the downloaded content hash matches the expected value, where
  ``ALGO`` is one of the algorithms supported by ``file(<HASH>)``.
  If it does not match, the operation fails with an error.

``EXPECTED_MD5 <value>``
  Historical short-hand for ``EXPECTED_HASH MD5=<value>``.

``TLS_VERIFY <ON|OFF>``
  Specify whether to verify the server certificate for ``https://`` URLs.
  The default is to *not* verify.

``TLS_CAINFO <file>``
  Specify a custom Certificate Authority file for ``https://`` URLs.

For ``https://`` URLs CMake must be built with OpenSSL support.  ``TLS/SSL``
certificates are not checked by default.  Set ``TLS_VERIFY`` to ``ON`` to
check certificates and/or use ``EXPECTED_HASH`` to verify downloaded content.
If neither ``TLS`` option is given CMake will check variables
``CMAKE_TLS_VERIFY`` and ``CMAKE_TLS_CAINFO``, respectively.

Locking
^^^^^^^

.. _LOCK:

.. code-block:: cmake

  file(LOCK <path> [DIRECTORY] [RELEASE]
       [GUARD <FUNCTION|FILE|PROCESS>]
       [RESULT_VARIABLE <variable>]
       [TIMEOUT <seconds>])

Lock a file specified by ``<path>`` if no ``DIRECTORY`` option present and file
``<path>/cmake.lock`` otherwise. File will be locked for scope defined by
``GUARD`` option (default value is ``PROCESS``). ``RELEASE`` option can be used
to unlock file explicitly. If option ``TIMEOUT`` is not specified CMake will
wait until lock succeed or until fatal error occurs. If ``TIMEOUT`` is set to
``0`` lock will be tried once and result will be reported immediately. If
``TIMEOUT`` is not ``0`` CMake will try to lock file for the period specified
by ``<seconds>`` value. Any errors will be interpreted as fatal if there is no
``RESULT_VARIABLE`` option. Otherwise result will be stored in ``<variable>``
and will be ``0`` on success or error message on failure.

Note that lock is advisory - there is no guarantee that other processes will
respect this lock, i.e. lock synchronize two or more CMake instances sharing
some modifiable resources. Similar logic applied to ``DIRECTORY`` option -
locking parent directory doesn't prevent other ``LOCK`` commands to lock any
child directory or file.

Trying to lock file twice is not allowed.  Any intermediate directories and
file itself will be created if they not exist.  ``GUARD`` and ``TIMEOUT``
options ignored on ``RELEASE`` operation.