string
------

String operations.

::

  string(REGEX MATCH <regular_expression>
         <output variable> <input> [<input>...])
  string(REGEX MATCHALL <regular_expression>
         <output variable> <input> [<input>...])
  string(REGEX REPLACE <regular_expression>
         <replace_expression> <output variable>
         <input> [<input>...])
  string(REPLACE <match_string>
         <replace_string> <output variable>
         <input> [<input>...])
  string(APPEND <string variable> [<input>...])
  string(CONCAT <output variable> [<input>...])
  string(<MD5|SHA1|SHA224|SHA256|SHA384|SHA512>
         <output variable> <input>)
  string(COMPARE EQUAL <string1> <string2> <output variable>)
  string(COMPARE NOTEQUAL <string1> <string2> <output variable>)
  string(COMPARE LESS <string1> <string2> <output variable>)
  string(COMPARE GREATER <string1> <string2> <output variable>)
  string(ASCII <number> [<number> ...] <output variable>)
  string(CONFIGURE <string1> <output variable>
         [@ONLY] [ESCAPE_QUOTES])
  string(TOUPPER <string1> <output variable>)
  string(TOLOWER <string1> <output variable>)
  string(LENGTH <string> <output variable>)
  string(SUBSTRING <string> <begin> <length> <output variable>)
  string(STRIP <string> <output variable>)
  string(RANDOM [LENGTH <length>] [ALPHABET <alphabet>]
         [RANDOM_SEED <seed>] <output variable>)
  string(FIND <string> <substring> <output variable> [REVERSE])
  string(TIMESTAMP <output variable> [<format string>] [UTC])
  string(MAKE_C_IDENTIFIER <input string> <output variable>)
  string(GENEX_STRIP <input string> <output variable>)
  string(UUID <output variable> NAMESPACE <namespace> NAME <name>
         TYPE <MD5|SHA1> [UPPER])

``REGEX MATCH`` will match the regular expression once and store the match
in the output variable.

``REGEX MATCHALL`` will match the regular expression as many times as
possible and store the matches in the output variable as a list.

``REGEX REPLACE`` will match the regular expression as many times as
possible and substitute the replacement expression for the match in
the output.  The replace expression may refer to paren-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.

``REPLACE`` will replace all occurrences of ``match_string`` in the input
with ``replace_string`` and store the result in the output.

``APPEND`` will append all the input arguments to the string.

``CONCAT`` will concatenate all the input arguments together and store
the result in the named output variable.

``MD5``, ``SHA1``, ``SHA224``, ``SHA256``, ``SHA384``, and ``SHA512`` will
compute a cryptographic hash of the input string.

``COMPARE EQUAL``/``COMPARE NOTEQUAL``/``COMPARE LESS/GREATER`` will
compare the strings and store true or false in the output variable.

``ASCII`` will convert all numbers into corresponding ASCII characters.

``CONFIGURE`` will transform a string like :command:`configure_file`
transforms a file.

``TOUPPER``/``TOLOWER`` will convert string to upper/lower characters.

``LENGTH`` will return a given string's length.

``SUBSTRING`` will return a substring of a given string. If length is -1
the remainder of the string starting at begin will be returned.
If string is shorter than length then end of string is used instead.

.. note::
  CMake 3.1 and below reported an error if length pointed past
  the end of string.

``STRIP`` will return a substring of a given string with leading and
trailing spaces removed.

``RANDOM`` will 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.

``FIND`` will 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 following characters have special meaning in regular expressions:

::

   ^         Matches at beginning of input
   $         Matches at end of input
   .         Matches any single character
   [ ]       Matches any character(s) inside the brackets
   [^ ]      Matches any character(s) not inside the brackets
    -        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. Additionally it is saved
             by all regular expression-related commands, including
             e.g. if( MATCHES ), in the variables CMAKE_MATCH_(0..9).

``*``, ``+`` 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".

``TIMESTAMP`` will write a string representation of the current date
and/or time to the output variable.

Should the command be 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:

::

   %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).
   %M        The minute of the current hour (00-59).
   %S        The second of the current minute.
             60 represents a leap second. (00-60)
   %U        The week number of the current year (00-53).
   %w        The day of the current week. 0 is Sunday. (0-6)
   %y        The last two digits of the current year (00-99)
   %Y        The current year.

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.

``MAKE_C_IDENTIFIER`` will write a string which can be used as an
identifier in C.

``GENEX_STRIP`` will strip any
:manual:`generator expressions <cmake-generator-expressions(7)>` from the
``input string`` and store the result in the ``output variable``.

``UUID`` creates a univerally 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.