string

String operations.

Search and Replace

FIND

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.

REPLACE

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.

Regular Expressions

REGEX MATCH

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.

REGEX MATCHALL

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.

REGEX REPLACE

string(REGEX REPLACE <regular_expression>
       <replace_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 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.

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 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.

Manipulation

APPEND

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

Append all the input arguments to the string.

CONCAT

string(CONCAT <output variable> [<input>...])

Concatenate all the input arguments together and store the result in the named output variable.

TOLOWER

string(TOLOWER <string1> <output variable>)

Convert string to lower characters.

TOUPPER

string(TOUPPER <string1> <output variable>)

Convert string to upper characters.

LENGTH

string(LENGTH <string> <output variable>)

Store in an output variable a given string’s length.

SUBSTRING

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 end of string is used instead.

Note

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

STRIP

string(STRIP <string> <output variable>)

Store in an output variable a substring of a given string with leading and trailing spaces removed.

GENEX_STRIP

string(GENEX_STRIP <input string> <output variable>)

Strip any generator expressions from the input string and store the result in the output variable.

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.

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.

Generation

ASCII

string(ASCII <number> [<number> ...] <output variable>)

Convert all numbers into corresponding ASCII characters.

CONFIGURE

string(CONFIGURE <string1> <output variable>
       [@ONLY] [ESCAPE_QUOTES])

Transform a string like configure_file() transforms a file.

RANDOM

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.

TIMESTAMP

string(TIMESTAMP <output variable> [<format string>] [UTC])

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:

%%        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).
%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).
%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.

string(MAKE_C_IDENTIFIER <input string> <output variable>)

Write a string which can be used as an identifier in C.

Note

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.

UUID

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

Create 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.