# string

String operations.

## Synopsis

    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 <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 | TYPE | LENGTH | REMOVE}
             <json-string> <member|index> [<member|index> ...])
      string(JSON <out-var> [ERROR_VARIABLE <error-var>]
             MEMBER <json-string>
             [<member|index> ...] <index>)
      string(JSON <out-var> [ERROR_VARIABLE <error-var>]
             SET <json-string>
             <member|index> [<member|index> ...] <value>)
      string(JSON <out-var> [ERROR_VARIABLE <error-var>]
             EQUAL <json-string1> <json-string2>)

## 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.

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

Zero-length matches are allowed in `MATCHALL` and `REPLACE`. Previously, they triggered an error.

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

### 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.

  Added in version 3.9: All regular expression-related commands, including e.g. `if(MATCHES)`, save subgroup 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. `[[\(\a\+\b\)]]`.

## Manipulation

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

  Added in version 3.4.

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

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

  Added in version 3.10.

  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>...])

  Added in version 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 `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.

  Changed in version 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.

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>)

  Added in version 3.1.

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

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

  Added in version 3.15.

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

## Comparison

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>`.

  Added in version 3.7: Added the `LESS_EQUAL` and `GREATER_EQUAL` options.

## Hashing

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

  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.

  Added in version 3.8: Added the `SHA3_*` hash algorithms.

## Generation

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

  Convert all numbers into corresponding ASCII characters.

string(HEX <string> <output_variable>)

  Added in version 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.

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

  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:

  `%%`

    Added in version 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`

    Added in version 3.7.

    Abbreviated month name (e.g. Oct).

  `%B`

    Added in version 3.10.

    Full month name (e.g. October).

  `%M`

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

  `%s`

    Added in version 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`

    Added in version 3.23.

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

  `%U`

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

  `%V`

    Added in version 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`

    Added in version 3.7.

    Abbreviated weekday name (e.g. Fri).

  `%A`

    Added in version 3.10.

    Full weekday name (e.g. Friday).

  `%y`

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

  `%Y`

    The current year.

  `%z`

    Added in version 3.26.

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

  `%Z`

    Added in version 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.

  Added in version 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.

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

  Added in version 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

Added in version 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 Quoted Argument to ensure the entire JSON string is passed as a single argument even if it contains semicolons.

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

  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.

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

  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`.

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

  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.

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

  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.

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

  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>`.

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

  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.

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

  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.