String operations.


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>...)

  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 <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>)

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

  string(<HASH> <out-var> <input>)

  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> ...)

Search and Replace

Search and Replace With Plain Strings

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.

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

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.

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.

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.

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


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

[^ ]

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_<n> for <n> 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.

CMake language 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 Bracket Argument without having to escape the backslashes, e.g. [[\(\a\+\b\)]].


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

Append all the <input> arguments to the string.

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

Prepend all the <input> arguments to the string.

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

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

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

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 list() command. This allows for the elements to have special characters like ; in them.

string(TOLOWER <string> <output_variable>)

Convert <string> to lower characters.

string(TOUPPER <string> <output_variable>)

Convert <string> to upper characters.

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.

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. If <string> is shorter than <length> then the end of the string is used instead.

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


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

string(STRIP <string> <output_variable>)

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

string(GENEX_STRIP <string> <output_variable>)

Strip any generator expressions from the input <string> and store the result in the <output_variable>.

string(REPEAT <string> <count> <output_variable>)

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


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>.


string(<HASH> <output_variable> <input>)

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


Message-Digest Algorithm 5, RFC 1321.


US Secure Hash Algorithm 1, RFC 3174.


US Secure Hash Algorithms, RFC 4634.


US Secure Hash Algorithms, RFC 4634.


US Secure Hash Algorithms, RFC 4634.


US Secure Hash Algorithms, RFC 4634.


Keccak SHA-3.


Keccak SHA-3.


Keccak SHA-3.


Keccak SHA-3.


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

Convert all numbers into corresponding ASCII characters.

string(HEX <string> <output_variable>)

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.

string(CONFIGURE <string> <output_variable>

Transform a <string> like configure_file() transforms a file.

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.

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.

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:

%%        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        Abbreviated month name (e.g. Oct).
%B        Full month name (e.g. October).
%M        The minute of the current hour (00-59).
%s        Seconds since midnight (UTC) 1-Jan-1970 (UNIX time).
%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)
%a        Abbreviated weekday name (e.g. Fri).
%A        Full weekday name (e.g. Friday).
%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.


If the SOURCE_DATE_EPOCH environment variable is set, its value will be used instead of the current time. See for details.

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

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.