file — CMake 3.12.0 Documentation

# file

File manipulation command.

## Synopsis

    Reading
      file(READ <filename> <out-var> [...])
      file(STRINGS <filename> <out-var> [...])
      file(<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> [...])

    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

    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).

    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

    file(STRINGS myfile.txt myfile)

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

    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 string(<HASH>) command.

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

## Writing

    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 `configure_file()` command to update the file only when its content changes.

    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.

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

Generate an output file for each build configuration supported by the current `CMake Generator`. Evaluate `generator expressions` 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 `CMAKE_CURRENT_SOURCE_DIR`. See 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 `CMAKE_CURRENT_BINARY_DIR`. See 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

    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 `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 `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

    file(RENAME <oldname> <newname>)

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

    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.

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

Create the given directories and their parents as needed.

    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 `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 `CMAKE_INSTALL_MESSAGE` variable), and `NO_SOURCE_PERMISSIONS` is default. Installation scripts generated by the `install()` command use this signature (with some undocumented options for internal use).

## Path Conversion

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

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

    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

    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

    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.