CMake/Help/command/string.rst

string
------

String operations.

Synopsis
^^^^^^^^

.. parsed-literal::

  `Search and Replace`_
    string(`FIND`_ <string> <substring> <out-var> [...])
    string(`REPLACE`_ <match-string> <replace-string> <out-var> <input>...)
    string(`REGEX MATCH`_ <match-regex> <out-var> <input>...)
    string(`REGEX MATCHALL`_ <match-regex> <out-var> <input>...)
    string(`REGEX REPLACE`_ <match-regex> <replace-expr> <out-var> <input>...)

  `Manipulation`_
    string(`APPEND`_ <string-var> [<input>...])
    string(`PREPEND`_ <string-var> [<input>...])
    string(`CONCAT`_ <out-var> [<input>...])
    string(`JOIN`_ <glue> <out-var> [<input>...])
    string(`TOLOWER`_ <string> <out-var>)
    string(`TOUPPER`_ <string> <out-var>)
    string(`LENGTH <LENGTH_>`_ <string> <out-var>)
    string(`SUBSTRING`_ <string> <begin> <length> <out-var>)
    string(`STRIP`_ <string> <out-var>)
    string(`GENEX_STRIP`_ <string> <out-var>)
    string(`REPEAT`_ <string> <count> <out-var>)

  `Comparison`_
    string(`COMPARE`_ <op> <string1> <string2> <out-var>)

  `Hashing`_
    string(`\<HASH\>`_ <out-var> <input>)

  `Generation`_
    string(`ASCII`_ <number>... <out-var>)
    string(`HEX`_ <string> <out-var>)
    string(`CONFIGURE`_ <string> <out-var> [...])
    string(`MAKE_C_IDENTIFIER`_ <string> <out-var>)
    string(`RANDOM`_ [<option>...] <out-var>)
    string(`TIMESTAMP`_ <out-var> [<format string>] [UTC])
    string(`UUID`_ <out-var> ...)

  `JSON`_
    string(JSON <out-var> [ERROR_VARIABLE <error-var>]
           {`GET <JSON GET_>`_ | `TYPE <JSON TYPE_>`_ | `LENGTH <JSON LENGTH_>`_ | `REMOVE <JSON REMOVE_>`_}
           <json-string> <member|index> [<member|index> ...])
    string(JSON <out-var> [ERROR_VARIABLE <error-var>]
           `MEMBER <JSON MEMBER_>`_ <json-string>
           [<member|index> ...] <index>)
    string(JSON <out-var> [ERROR_VARIABLE <error-var>]
           `SET <JSON SET_>`_ <json-string>
           <member|index> [<member|index> ...] <value>)
    string(JSON <out-var> [ERROR_VARIABLE <error-var>]
           `EQUAL <JSON EQUAL_>`_ <json-string1> <json-string2>)

Search and Replace
^^^^^^^^^^^^^^^^^^

Search and Replace With Plain Strings
"""""""""""""""""""""""""""""""""""""

.. signature::
  string(FIND <string> <substring> <output_variable> [REVERSE])

  Return the position where the given ``<substring>`` was found in
  the supplied ``<string>``.  If the ``REVERSE`` flag was used, the command
  will search for the position of the last occurrence of the specified
  ``<substring>``.  If the ``<substring>`` is not found, a position of -1 is
  returned.

  The ``string(FIND)`` subcommand treats all strings as ASCII-only characters.
  The index stored in ``<output_variable>`` will also be counted in bytes,
  so strings containing multi-byte characters may lead to unexpected results.

.. signature::
  string(REPLACE <match_string>
         <replace_string> <output_variable>
         <input> [<input>...])

  Replace all occurrences of ``<match_string>`` in the ``<input>``
  with ``<replace_string>`` and store the result in the ``<output_variable>``.

Search and Replace With Regular Expressions
"""""""""""""""""""""""""""""""""""""""""""

.. signature::
  string(REGEX MATCH <regular_expression>
         <output_variable> <input> [<input>...])

  Match the ``<regular_expression>`` once and store the match in the
  ``<output_variable>``.
  All ``<input>`` arguments are concatenated before matching.
  Regular expressions are specified in the subsection just below.

.. signature::
  string(REGEX MATCHALL <regular_expression>
         <output_variable> <input> [<input>...])

  Match the ``<regular_expression>`` as many times as possible and store the
  matches in the ``<output_variable>`` as a list.
  All ``<input>`` arguments are concatenated before matching.

.. signature::
  string(REGEX REPLACE <regular_expression>
         <replacement_expression> <output_variable>
         <input> [<input>...])

  Match the ``<regular_expression>`` as many times as possible and substitute
  the ``<replacement_expression>`` for the match in the output.
  All ``<input>`` arguments are concatenated before matching.

  The ``<replacement_expression>`` may refer to parenthesis-delimited
  subexpressions of the match using ``\1``, ``\2``, ..., ``\9``.  Note that
  two backslashes (``\\1``) are required in CMake code to get a backslash
  through argument parsing.

.. versionchanged:: 4.1
  The ``^`` anchor now matches only at the beginning of the input
  string instead of the beginning of each repeated search.
  See policy :policy:`CMP0186`.

  The replacement expression may contain references to subexpressions that
  didn't match anything. Previously, such references triggered an error.

.. _`Regex Specification`:

Regex Specification
"""""""""""""""""""

The following characters have special meaning in regular expressions:

``^``
  Matches at beginning of input
``$``
  Matches at end of input
``.``
  Matches any single character
``\<char>``
  Matches the single character specified by ``<char>``.  Use this to
  match special regex characters, e.g. ``\.`` for a literal ``.``
  or ``\\`` for a literal backslash ``\``.  Escaping a non-special
  character is unnecessary but allowed, e.g. ``\a`` matches ``a``.
``[ ]``
  Matches any character(s) inside the brackets.
  To match a literal ``]``, make it the first character, e.g., ``[]ab]``.
``[^ ]``
  Matches any character(s) not inside the brackets.
  To not match a literal ``]``, make it the first character, e.g., ``[^]ab]``.
``-``
  Inside brackets, specifies an inclusive range between characters on
  either side, e.g., ``[a-f]`` is ``[abcdef]``.
  To match a literal ``-`` using brackets, make it the first or the last
  character, e.g., ``[+*/-]`` matches basic mathematical operators.
``*``
  Matches preceding pattern zero or more times
``+``
  Matches preceding pattern one or more times
``?``
  Matches preceding pattern zero or once only
``|``
  Matches a pattern on either side of the ``|``
``()``
  Saves a matched subexpression, which can be referenced
  in the ``REGEX REPLACE`` operation.

  .. versionadded:: 3.9
    All regular expression-related commands, including e.g.
    :command:`if(MATCHES)`, save subgroup matches in the variables
    :variable:`CMAKE_MATCH_<n>` for ``<n>`` 0..9.

.. noqa: spellcheck off

``*``, ``+`` and ``?`` have higher precedence than concatenation.  ``|``
has lower precedence than concatenation.  This means that the regular
expression ``^ab+d$`` matches ``abbd`` but not ``ababd``, and the regular
expression ``^(ab|cd)$`` matches ``ab`` but not ``abd``.

.. noqa: spellcheck on

CMake language :ref:`Escape Sequences` such as ``\t``, ``\r``, ``\n``,
and ``\\`` may be used to construct literal tabs, carriage returns,
newlines, and backslashes (respectively) to pass in a regex.  For example:

* The quoted argument ``"[ \t\r\n]"`` specifies a regex that matches
  any single whitespace character.
* The quoted argument ``"[/\\]"`` specifies a regex that matches
  a single forward slash ``/`` or backslash ``\``.
* The quoted argument ``"[A-Za-z0-9_]"`` specifies a regex that matches
  any single "word" character in the C locale.
* The quoted argument ``"\\(\\a\\+b\\)"`` specifies a regex that matches
  the exact string ``(a+b)``.  Each ``\\`` is parsed in a quoted argument
  as just ``\``, so the regex itself is actually ``\(\a\+\b\)``.  This
  can alternatively be specified in a :ref:`bracket argument` without
  having to escape the backslashes, e.g. ``[[\(\a\+\b\)]]``.

Manipulation
^^^^^^^^^^^^

.. signature::
  string(APPEND <string_variable> [<input>...])

  .. versionadded:: 3.4

  Append all the ``<input>`` arguments to the string.

.. signature::
  string(PREPEND <string_variable> [<input>...])

  .. versionadded:: 3.10

  Prepend all the ``<input>`` arguments to the string.

.. signature::
  string(CONCAT <output_variable> [<input>...])

  Concatenate all the ``<input>`` arguments together and store
  the result in the named ``<output_variable>``.

.. signature::
  string(JOIN <glue> <output_variable> [<input>...])

  .. versionadded:: 3.12

  Join all the ``<input>`` arguments together using the ``<glue>``
  string and store the result in the named ``<output_variable>``.

  To join a list's elements, prefer to use the ``JOIN`` operator
  from the :command:`list` command.  This allows for the elements to have
  special characters like ``;`` in them.

.. signature::
  string(TOLOWER <string> <output_variable>)

  Convert ``<string>`` to lower characters.

.. signature::
  string(TOUPPER <string> <output_variable>)

  Convert ``<string>`` to upper characters.

.. signature::
  string(LENGTH <string> <output_variable>)

  Store in an ``<output_variable>`` a given string's length in bytes.
  Note that this means if ``<string>`` contains multi-byte characters,
  the result stored in ``<output_variable>`` will *not* be
  the number of characters.

.. signature::
  string(SUBSTRING <string> <begin> <length> <output_variable>)

  Store in an ``<output_variable>`` a substring of a given ``<string>``.  If
  ``<length>`` is ``-1`` the remainder of the string starting at ``<begin>``
  will be returned.

  .. versionchanged:: 3.2
    If ``<string>`` is shorter than ``<length>``
    then the end of the string is used instead.
    Previous versions of CMake reported an error in this case.

  Both ``<begin>`` and ``<length>`` are counted in bytes, so care must
  be exercised if ``<string>`` could contain multi-byte characters.

.. signature::
  string(STRIP <string> <output_variable>)

  Store in an ``<output_variable>`` a substring of a given ``<string>``
  with leading and trailing spaces removed.

.. signature::
  string(GENEX_STRIP <string> <output_variable>)

  .. versionadded:: 3.1

  Strip any :manual:`generator expressions <cmake-generator-expressions(7)>`
  from the input ``<string>`` and store the result
  in the ``<output_variable>``.

.. signature::
  string(REPEAT <string> <count> <output_variable>)

  .. versionadded:: 3.15

  Produce the output string as the input ``<string>``
  repeated ``<count>`` times.

Comparison
^^^^^^^^^^

.. _COMPARE:

.. signature::
  string(COMPARE LESS <string1> <string2> <output_variable>)
  string(COMPARE GREATER <string1> <string2> <output_variable>)
  string(COMPARE EQUAL <string1> <string2> <output_variable>)
  string(COMPARE NOTEQUAL <string1> <string2> <output_variable>)
  string(COMPARE LESS_EQUAL <string1> <string2> <output_variable>)
  string(COMPARE GREATER_EQUAL <string1> <string2> <output_variable>)

  Compare the strings and store true or false in the ``<output_variable>``.

  .. versionadded:: 3.7
    Added the ``LESS_EQUAL`` and ``GREATER_EQUAL`` options.

.. _`Supported Hash Algorithms`:

Hashing
^^^^^^^

.. signature::
  string(<HASH> <output_variable> <input>)
  :target: <HASH>

  Compute a cryptographic hash of the ``<input>`` string.
  The supported ``<HASH>`` algorithm names are:

  ``MD5``
    Message-Digest Algorithm 5, RFC 1321.
  ``SHA1``
    US Secure Hash Algorithm 1, RFC 3174.
  ``SHA224``
    US Secure Hash Algorithms, RFC 4634.
  ``SHA256``
    US Secure Hash Algorithms, RFC 4634.
  ``SHA384``
    US Secure Hash Algorithms, RFC 4634.
  ``SHA512``
    US Secure Hash Algorithms, RFC 4634.
  ``SHA3_224``
    Keccak SHA-3.
  ``SHA3_256``
    Keccak SHA-3.
  ``SHA3_384``
    Keccak SHA-3.
  ``SHA3_512``
    Keccak SHA-3.

  .. versionadded:: 3.8
    Added the ``SHA3_*`` hash algorithms.

Generation
^^^^^^^^^^

.. signature::
  string(ASCII <number> [<number> ...] <output_variable>)

  Convert all numbers into corresponding ASCII characters.

.. signature::
  string(HEX <string> <output_variable>)

  .. versionadded:: 3.18

  Convert each byte in the input ``<string>`` to its hexadecimal representation
  and store the concatenated hex digits in the ``<output_variable>``.
  Letters in the output (``a`` through ``f``) are in lowercase.

.. signature::
  string(CONFIGURE <string> <output_variable>
         [@ONLY] [ESCAPE_QUOTES])

  Transform a ``<string>`` like :command:`configure_file` transforms a file.

.. signature::
  string(MAKE_C_IDENTIFIER <string> <output_variable>)

  Convert each non-alphanumeric character in the input ``<string>`` to an
  underscore and store the result in the ``<output_variable>``.  If the first
  character of the ``<string>`` is a digit, an underscore will also be
  prepended to the result.

.. signature::
  string(RANDOM [LENGTH <length>] [ALPHABET <alphabet>]
         [RANDOM_SEED <seed>] <output_variable>)

  Return a random string of given ``<length>`` consisting of
  characters from the given ``<alphabet>``.  Default length is 5 characters
  and default alphabet is all numbers and upper and lower case letters.
  If an integer ``RANDOM_SEED`` is given, its value will be used to seed the
  random number generator.

.. signature::
  string(TIMESTAMP <output_variable> [<format_string>] [UTC])

  Write a string representation of the current date
  and/or time to the ``<output_variable>``.

  If the command is unable to obtain a timestamp, the ``<output_variable>``
  will be set to the empty string ``""``.

  The optional ``UTC`` flag requests the current date/time representation to
  be in Coordinated Universal Time (UTC) rather than local time.

  The optional ``<format_string>`` may contain the following format
  specifiers:

  ``%%``
    .. versionadded:: 3.8

    A literal percent sign (%).

  ``%d``
    The day of the current month (01-31).

  ``%H``
    The hour on a 24-hour clock (00-23).

  ``%I``
    The hour on a 12-hour clock (01-12).

  ``%j``
    The day of the current year (001-366).

  ``%m``
    The month of the current year (01-12).

  ``%b``
    .. versionadded:: 3.7

    Abbreviated month name (e.g. Oct).

  ``%B``
    .. versionadded:: 3.10

    Full month name (e.g. October).

  ``%M``
    The minute of the current hour (00-59).

  ``%s``
    .. versionadded:: 3.6

    Seconds since midnight (UTC) 1-Jan-1970 (UNIX time).

  ``%S``
    The second of the current minute.  60 represents a leap second. (00-60)

  ``%f``
    .. versionadded:: 3.23

    The microsecond of the current second (000000-999999).

  ``%U``
    The week number of the current year (00-53).

  ``%V``
    .. versionadded:: 3.22

    The ISO 8601 week number of the current year (01-53).

  ``%w``
    The day of the current week. 0 is Sunday. (0-6)

  ``%a``
    .. versionadded:: 3.7

    Abbreviated weekday name (e.g. Fri).

  ``%A``
    .. versionadded:: 3.10

    Full weekday name (e.g. Friday).

  ``%y``
    The last two digits of the current year (00-99).

  ``%Y``
    The current year.

  ``%z``
    .. versionadded:: 3.26

    The offset of the time zone from UTC, in hours and minutes,
    with format ``+hhmm`` or ``-hhmm``.

  ``%Z``
    .. versionadded:: 3.26

    The time zone name.

  Unknown format specifiers will be ignored and copied to the output
  as-is.

  If no explicit ``<format_string>`` is given, it will default to:

  * ``%Y-%m-%dT%H:%M:%S`` for local time.
  * ``%Y-%m-%dT%H:%M:%SZ`` for UTC.

  .. versionadded:: 3.8
    If the ``SOURCE_DATE_EPOCH`` environment variable is set,
    its value will be used instead of the current time.
    See https://reproducible-builds.org/specs/source-date-epoch/ for details.

.. signature::
  string(UUID <output_variable> NAMESPACE <namespace> NAME <name>
         TYPE <MD5|SHA1> [UPPER])

  .. versionadded:: 3.1

  Create a universally unique identifier (aka GUID) as per RFC4122
  based on the hash of the combined values of ``<namespace>``
  (which itself has to be a valid UUID) and ``<name>``.
  The hash algorithm can be either ``MD5`` (Version 3 UUID) or
  ``SHA1`` (Version 5 UUID).
  A UUID has the format ``xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx``
  where each ``x`` represents a lower case hexadecimal character.
  Where required, an uppercase representation can be requested
  with the optional ``UPPER`` flag.

.. _JSON:

JSON
^^^^

.. versionadded:: 3.19

Functionality for querying a JSON string.

.. note::
  In each of the following JSON-related subcommands, if the optional
  ``ERROR_VARIABLE`` argument is given, errors will be reported in
  ``<error-variable>`` and the ``<out-var>`` will be set to
  ``<member|index>-[<member|index>...]-NOTFOUND`` with the path elements
  up to the point where the error occurred, or just ``NOTFOUND`` if there
  is no relevant path.  If an error occurs but the ``ERROR_VARIABLE``
  option is not present, a fatal error message is generated.  If no error
  occurs, the ``<error-variable>`` will be set to ``NOTFOUND``.

In the following subcommands, the ``<json-string>`` argument should
be written as a :ref:`Quoted Argument` to ensure the entire JSON
string is passed as a single argument even if it contains semicolons.

.. signature::
  string(JSON <out-var> [ERROR_VARIABLE <error-variable>]
         GET <json-string> <member|index> [<member|index> ...])
  :target: JSON GET

  Get an element from ``<json-string>`` at the location given
  by the list of ``<member|index>`` arguments.
  Array and object elements will be returned as a JSON string.
  Boolean elements will be returned as ``ON`` or ``OFF``.
  Null elements will be returned as an empty string.
  Number and string types will be returned as strings.

.. signature::
  string(JSON <out-var> [ERROR_VARIABLE <error-variable>]
         TYPE <json-string> <member|index> [<member|index> ...])
  :target: JSON TYPE

  Get the type of an element in ``<json-string>`` at the location
  given by the list of ``<member|index>`` arguments. The ``<out-var>``
  will be set to one of ``NULL``, ``NUMBER``, ``STRING``, ``BOOLEAN``,
  ``ARRAY``, or ``OBJECT``.

.. signature::
  string(JSON <out-var> [ERROR_VARIABLE <error-var>]
         MEMBER <json-string>
         [<member|index> ...] <index>)
  :target: JSON MEMBER

  Get the name of the ``<index>``-th member in ``<json-string>``
  at the location given by the list of ``<member|index>`` arguments.
  Requires an element of object type.

.. signature::
  string(JSON <out-var> [ERROR_VARIABLE <error-variable>]
         LENGTH <json-string> [<member|index> ...])
  :target: JSON LENGTH

  Get the length of an element in ``<json-string>`` at the location
  given by the list of ``<member|index>`` arguments.
  Requires an element of array or object type.

.. signature::
  string(JSON <out-var> [ERROR_VARIABLE <error-variable>]
         REMOVE <json-string> <member|index> [<member|index> ...])
  :target: JSON REMOVE

  Remove an element from ``<json-string>`` at the location
  given by the list of ``<member|index>`` arguments. The JSON string
  without the removed element will be stored in ``<out-var>``.

.. signature::
  string(JSON <out-var> [ERROR_VARIABLE <error-variable>]
         SET <json-string> <member|index> [<member|index> ...] <value>)
  :target: JSON SET

  Set an element in ``<json-string>`` at the location
  given by the list of ``<member|index>`` arguments to ``<value>``.
  The contents of ``<value>`` should be valid JSON.
  If ``<json-string>`` is an array, ``<value>`` can be appended to the end of
  the array by using a number greater or equal to the array length as the
  ``<member|index>`` argument.

.. signature::
  string(JSON <out-var> [ERROR_VARIABLE <error-var>]
         EQUAL <json-string1> <json-string2>)
  :target: JSON EQUAL

  Compare the two JSON objects given by ``<json-string1>``
  and ``<json-string2>`` for equality.  The contents of ``<json-string1>``
  and ``<json-string2>`` should be valid JSON.  The ``<out-var>``
  will be set to a true value if the JSON objects are considered equal,
  or a false value otherwise.