cmake_path

New in version 3.20.

This command is for the manipulation of paths. Only syntactic aspects of paths are handled, there is no interaction of any kind with any underlying file system. The path may represent a non-existing path or even one that is not allowed to exist on the current file system or platform. For operations that do interact with the filesystem, see the file() command.

Note

The cmake_path command handles paths in the format of the build system (i.e. the host platform), not the target system. When cross-compiling, if the path contains elements that are not representable on the host platform (e.g. a drive letter when the host is not Windows), the results will be unpredictable.

Synopsis

Conventions

Path Structure And Terminology

Normalization

Decomposition
  cmake_path(GET <path-var> ROOT_NAME <out-var>)
  cmake_path(GET <path-var> ROOT_DIRECTORY <out-var>)
  cmake_path(GET <path-var> ROOT_PATH <out-var>)
  cmake_path(GET <path-var> FILENAME <out-var>)
  cmake_path(GET <path-var> EXTENSION [LAST_ONLY] <out-var>)
  cmake_path(GET <path-var> STEM [LAST_ONLY] <out-var>)
  cmake_path(GET <path-var> RELATIVE_PART <out-var>)
  cmake_path(GET <path-var> PARENT_PATH <out-var>)

Query
  cmake_path(HAS_ROOT_NAME <path-var> <out-var>)
  cmake_path(HAS_ROOT_DIRECTORY <path-var> <out-var>)
  cmake_path(HAS_ROOT_PATH <path-var> <out-var>)
  cmake_path(HAS_FILENAME <path-var> <out-var>)
  cmake_path(HAS_EXTENSION <path-var> <out-var>)
  cmake_path(HAS_STEM <path-var> <out-var>)
  cmake_path(HAS_RELATIVE_PART <path-var> <out-var>)
  cmake_path(HAS_PARENT_PATH <path-var> <out-var>)
  cmake_path(IS_ABSOLUTE <path-var> <out-var>)
  cmake_path(IS_RELATIVE <path-var> <out-var>)
  cmake_path(IS_PREFIX <path-var> <input> [NORMALIZE] <out-var>)
  cmake_path(COMPARE <input1> <OP> <input2> <out-var>)

Modification
  cmake_path(SET <path-var> [NORMALIZE] <input>)
  cmake_path(APPEND <path-var> [<input>...] [OUTPUT_VARIABLE <out-var>])
  cmake_path(APPEND_STRING <path-var> [<input>...] [OUTPUT_VARIABLE <out-var>])
  cmake_path(REMOVE_FILENAME <path-var> [OUTPUT_VARIABLE <out-var>])
  cmake_path(REPLACE_FILENAME <path-var> <input> [OUTPUT_VARIABLE <out-var>])
  cmake_path(REMOVE_EXTENSION <path-var> [LAST_ONLY] [OUTPUT_VARIABLE <out-var>])
  cmake_path(REPLACE_EXTENSION <path-var> [LAST_ONLY] <input> [OUTPUT_VARIABLE <out-var>])

Generation
  cmake_path(NORMAL_PATH <path-var> [OUTPUT_VARIABLE <out-var>])
  cmake_path(RELATIVE_PATH <path-var> [BASE_DIRECTORY <input>] [OUTPUT_VARIABLE <out-var>])
  cmake_path(ABSOLUTE_PATH <path-var> [BASE_DIRECTORY <input>] [NORMALIZE] [OUTPUT_VARIABLE <out-var>])

Native Conversion
  cmake_path(NATIVE_PATH <path-var> [NORMALIZE] <out-var>)
  cmake_path(CONVERT <input> TO_CMAKE_PATH_LIST <out-var>)
  cmake_path(CONVERT <input> TO_NATIVE_PATH_LIST <out-var>)

Hashing
  cmake_path(HASH <path-var> <out-var>)

Conventions

The following conventions are used in this command's documentation:

<path-var>

Always the name of a variable. For commands that expect a <path-var> as input, the variable must exist and it is expected to hold a single path.

<input>

A string literal which may contain a path, path fragment, or multiple paths with a special separator depending on the command. See the description of each command to see how this is interpreted.

<input>...

Zero or more string literal arguments.

<out-var>

The name of a variable into which the result of a command will be written.

Path Structure And Terminology

A path has the following structure (all components are optional, with some constraints):

root-name root-directory-separator (item-name directory-separator)* filename
root-name

Identifies the root on a filesystem with multiple roots (such as "C:" or "//myserver"). It is optional.

root-directory-separator

A directory separator that, if present, indicates that this path is absolute. If it is missing and the first element other than the root-name is an item-name, then the path is relative.

item-name

A sequence of characters that aren't directory separators. This name may identify a file, a hard link, a symbolic link, or a directory. Two special cases are recognized:

  • The item name consisting of a single dot character . is a directory name that refers to the current directory.

  • The item name consisting of two dot characters .. is a directory name that refers to the parent directory.

The (...)* pattern shown above is to indicate that there can be zero or more item names, with multiple items separated by a directory-separator. The ()* characters are not part of the path.

directory-separator

The only recognized directory separator is a forward slash character /. If this character is repeated, it is treated as a single directory separator. In other words, /usr///////lib is the same as /usr/lib.

filename

A path has a filename if it does not end with a directory-separator. The filename is effectively the last item-name of the path, so it can also be a hard link, symbolic link or a directory.

A filename can have an extension. By default, the extension is defined as the sub-string beginning at the left-most period (including the period) and until the end of the filename. In commands that accept a LAST_ONLY keyword, LAST_ONLY changes the interpretation to the sub-string beginning at the right-most period.

The following exceptions apply to the above interpretation:

  • If the first character in the filename is a period, that period is ignored (i.e. a filename like ".profile" is treated as having no extension).

  • If the filename is either . or .., it has no extension.

The stem is the part of the filename before the extension.

Some commands refer to a root-path. This is the concatenation of root-name and root-directory-separator, either or both of which can be empty. A relative-part refers to the full path with any root-path removed.

Creating A Path Variable

While a path can be created with care using an ordinary set() command, it is recommended to use cmake_path(SET) instead, as it automatically converts the path to the required form where required. The cmake_path(APPEND) subcommand may be another suitable alternative where a path needs to be constructed by joining fragments. The following example compares the three methods for constructing the same path:

set(path1 "${CMAKE_CURRENT_SOURCE_DIR}/data")

cmake_path(SET path2 "${CMAKE_CURRENT_SOURCE_DIR}/data")

cmake_path(APPEND path3 "${CMAKE_CURRENT_SOURCE_DIR}" "data")

Modification and Generation sub-commands can either store the result in-place, or in a separate variable named after an OUTPUT_VARIABLE keyword. All other sub-commands store the result in a mandatory <out-var> variable.

Normalization

Some sub-commands support normalizing a path. The algorithm used to normalize a path is as follows:

  1. If the path is empty, stop (the normalized form of an empty path is also an empty path).

  2. Replace each directory-separator, which may consist of multiple separators, with a single / (/a///b  --> /a/b).

  3. Remove each solitary period (.) and any immediately following directory-separator (/a/./b/. --> /a/b).

  4. Remove each item-name (other than ..) that is immediately followed by a directory-separator and a .., along with any immediately following directory-separator (/a/b/../c --> a/c).

  5. If there is a root-directory, remove any .. and any directory-separators immediately following them. The parent of the root directory is treated as still the root directory (/../a --> /a).

  6. If the last item-name is .., remove any trailing directory-separator (../ --> ..).

  7. If the path is empty by this stage, add a dot (normal form of ./ is .).

Decomposition

The following forms of the GET subcommand each retrieve a different component or group of components from a path. See Path Structure And Terminology for the meaning of each path component.

cmake_path(GET <path-var> ROOT_NAME <out-var>)
cmake_path(GET <path-var> ROOT_DIRECTORY <out-var>)
cmake_path(GET <path-var> ROOT_PATH <out-var>)
cmake_path(GET <path-var> FILENAME <out-var>)
cmake_path(GET <path-var> EXTENSION [LAST_ONLY] <out-var>)
cmake_path(GET <path-var> STEM [LAST_ONLY] <out-var>)
cmake_path(GET <path-var> RELATIVE_PART <out-var>)
cmake_path(GET <path-var> PARENT_PATH <out-var>)

If a requested component is not present in the path, an empty string will be stored in <out-var>. For example, only Windows systems have the concept of a root-name, so when the host machine is non-Windows, the ROOT_NAME subcommand will always return an empty string.

For PARENT_PATH, if the HAS_RELATIVE_PART subcommand returns false, the result is a copy of <path-var>. Note that this implies that a root directory is considered to have a parent, with that parent being itself. Where HAS_RELATIVE_PART returns true, the result will essentially be <path-var> with one less element.

Root examples

set(path "c:/a")

cmake_path(GET path ROOT_NAME rootName)
cmake_path(GET path ROOT_DIRECTORY rootDir)
cmake_path(GET path ROOT_PATH rootPath)

message("Root name is \"${rootName}\"")
message("Root directory is \"${rootDir}\"")
message("Root path is \"${rootPath}\"")
Root name is "c:"
Root directory is "/"
Root path is "c:/"

Filename examples

set(path "/a/b")
cmake_path(GET path FILENAME filename)
message("First filename is \"${filename}\"")

# Trailing slash means filename is empty
set(path "/a/b/")
cmake_path(GET path FILENAME filename)
message("Second filename is \"${filename}\"")
First filename is "b"
Second filename is ""

Extension and stem examples

set(path "name.ext1.ext2")

cmake_path(GET path EXTENSION fullExt)
cmake_path(GET path STEM fullStem)
message("Full extension is \"${fullExt}\"")
message("Full stem is \"${fullStem}\"")

# Effect of LAST_ONLY
cmake_path(GET path EXTENSION LAST_ONLY lastExt)
cmake_path(GET path STEM LAST_ONLY lastStem)
message("Last extension is \"${lastExt}\"")
message("Last stem is \"${lastStem}\"")

# Special cases
set(dotPath "/a/.")
set(dotDotPath "/a/..")
set(someMorePath "/a/.some.more")
cmake_path(GET dotPath EXTENSION dotExt)
cmake_path(GET dotPath STEM dotStem)
cmake_path(GET dotDotPath EXTENSION dotDotExt)
cmake_path(GET dotDotPath STEM dotDotStem)
cmake_path(GET dotMorePath EXTENSION someMoreExt)
cmake_path(GET dotMorePath STEM someMoreStem)
message("Dot extension is \"${dotExt}\"")
message("Dot stem is \"${dotStem}\"")
message("Dot-dot extension is \"${dotDotExt}\"")
message("Dot-dot stem is \"${dotDotStem}\"")
message(".some.more extension is \"${someMoreExt}\"")
message(".some.more stem is \"${someMoreStem}\"")
Full extension is ".ext1.ext2"
Full stem is "name"
Last extension is ".ext2"
Last stem is "name.ext1"
Dot extension is ""
Dot stem is "."
Dot-dot extension is ""
Dot-dot stem is ".."
.some.more extension is ".more"
.some.more stem is ".some"

Relative part examples

set(path "c:/a/b")
cmake_path(GET path RELATIVE_PART result)
message("Relative part is \"${result}\"")

set(path "c/d")
cmake_path(GET path RELATIVE_PART result)
message("Relative part is \"${result}\"")

set(path "/")
cmake_path(GET path RELATIVE_PART result)
message("Relative part is \"${result}\"")
Relative part is "a/b"
Relative part is "c/d"
Relative part is ""

Path traversal examples

set(path "c:/a/b")
cmake_path(GET path PARENT_PATH result)
message("Parent path is \"${result}\"")

set(path "c:/")
cmake_path(GET path PARENT_PATH result)
message("Parent path is \"${result}\"")
Parent path is "c:/a"
Parent path is "c:/"

Query

Each of the GET subcommands has a corresponding HAS_... subcommand which can be used to discover whether a particular path component is present. See Path Structure And Terminology for the meaning of each path component.

cmake_path(HAS_ROOT_NAME <path-var> <out-var>)
cmake_path(HAS_ROOT_DIRECTORY <path-var> <out-var>)
cmake_path(HAS_ROOT_PATH <path-var> <out-var>)
cmake_path(HAS_FILENAME <path-var> <out-var>)
cmake_path(HAS_EXTENSION <path-var> <out-var>)
cmake_path(HAS_STEM <path-var> <out-var>)
cmake_path(HAS_RELATIVE_PART <path-var> <out-var>)
cmake_path(HAS_PARENT_PATH <path-var> <out-var>)

Each of the above follows the predictable pattern of setting <out-var> to true if the path has the associated component, or false otherwise. Note the following special cases:

  • For HAS_ROOT_PATH, a true result will only be returned if at least one of root-name or root-directory is non-empty.

  • For HAS_PARENT_PATH, the root directory is also considered to have a parent, which will be itself. The result is true except if the path consists of just a filename.

cmake_path(IS_ABSOLUTE <path-var> <out-var>)

Sets <out-var> to true if <path-var> is absolute. An absolute path is a path that unambiguously identifies the location of a file without reference to an additional starting location. On Windows, this means the path must have both a root-name and a root-directory-separator to be considered absolute. On other platforms, just a root-directory-separator is sufficient. Note that this means on Windows, IS_ABSOLUTE can be false while HAS_ROOT_DIRECTORY can be true.

cmake_path(IS_RELATIVE <path-var> <out-var>)

This will store the opposite of IS_ABSOLUTE in <out-var>.

cmake_path(IS_PREFIX <path-var> <input> [NORMALIZE] <out-var>)

Checks if <path-var> is the prefix of <input>.

When the NORMALIZE option is specified, <path-var> and <input> are normalized before the check.

set(path "/a/b/c/d")
cmake_path(IS_PREFIX path "/a/b" result)    # result = true
cmake_path(IS_PREFIX path "/x/y/z" result)  # result = false

set(path "/a/b")
cmake_path(IS_PREFIX path "/a/c/../b" NORMALIZE result)   # result = true
cmake_path(COMPARE <input1> EQUAL <input2> <out-var>)
cmake_path(COMPARE <input1> NOT_EQUAL <input2> <out-var>)

Compares the lexical representations of two paths provided as string literals. No normalization is performed on either path. Equality is determined according to the following pseudo-code logic:

if(NOT <input1>.root_name() STREQUAL <input2>.root_name())
  return FALSE

if(<input1>.has_root_directory() XOR <input2>.has_root_directory())
  return FALSE

Return FALSE if a relative portion of <input1> is not lexicographically
equal to the relative portion of <input2>. This comparison is performed path
component-wise. If all of the components compare equal, then return TRUE.

Note

Unlike most other cmake_path() subcommands, the COMPARE subcommand takes literal strings as input, not the names of variables.

Modification

cmake_path(SET <path-var> [NORMALIZE] <input>)

Assign the <input> path to <path-var>. If <input> is a native path, it is converted into a cmake-style path with forward-slashes (/). On Windows, the long filename marker is taken into account.

When the NORMALIZE option is specified, the path is normalized before the conversion.

For example:

set(native_path "c:\\a\\b/..\\c")
cmake_path(SET path "${native_path}")
message("CMake path is \"${path}\"")

cmake_path(SET path NORMALIZE "${native_path}")
message("Normalized CMake path is \"${path}\"")

Output:

CMake path is "c:/a/b/../c"
Normalized CMake path is "c:/a/c"
cmake_path(APPEND <path-var> [<input>...] [OUTPUT_VARIABLE <out-var>])

Append all the <input> arguments to the <path-var> using / as the directory-separator. Depending on the <input>, the previous contents of <path-var> may be discarded. For each <input> argument, the following algorithm (pseudo-code) applies:

# <path> is the contents of <path-var>

if(<input>.is_absolute() OR
   (<input>.has_root_name() AND
    NOT <input>.root_name() STREQUAL <path>.root_name()))
  replace <path> with <input>
  return()
endif()

if(<input>.has_root_directory())
  remove any root-directory and the entire relative path from <path>
elseif(<path>.has_filename() OR
       (NOT <path-var>.has_root_directory() OR <path>.is_absolute()))
  append directory-separator to <path>
endif()

append <input> omitting any root-name to <path>
cmake_path(APPEND_STRING <path-var> [<input>...] [OUTPUT_VARIABLE <out-var>])

Append all the <input> arguments to the <path-var> without adding any directory-separator.

cmake_path(REMOVE_FILENAME <path-var> [OUTPUT_VARIABLE <out-var>])

Removes the filename component (as returned by GET ... FILENAME) from <path-var>. After removal, any trailing directory-separator is left alone, if present.

If OUTPUT_VARIABLE is not given, then after this function returns, HAS_FILENAME returns false for <path-var>.

For example:

set(path "/a/b")
cmake_path(REMOVE_FILENAME path)
message("First path is \"${path}\"")

# filename is now already empty, the following removes nothing
cmake_path(REMOVE_FILENAME path)
message("Second path is \"${result}\"")

Output:

First path is "/a/"
Second path is "/a/"
cmake_path(REPLACE_FILENAME <path-var> <input> [OUTPUT_VARIABLE <out-var>])

Replaces the filename component from <path-var> with <input>. If <path-var> has no filename component (i.e. HAS_FILENAME returns false), the path is unchanged. The operation is equivalent to the following:

cmake_path(HAS_FILENAME path has_filename)
if(has_filename)
  cmake_path(REMOVE_FILENAME path)
  cmake_path(APPEND path input);
endif()
cmake_path(REMOVE_EXTENSION <path-var> [LAST_ONLY]
                                       [OUTPUT_VARIABLE <out-var>])

Removes the extension, if any, from <path-var>.

cmake_path(REPLACE_EXTENSION <path-var> [LAST_ONLY] <input>
                             [OUTPUT_VARIABLE <out-var>])

Replaces the extension with <input>. Its effect is equivalent to the following:

cmake_path(REMOVE_EXTENSION path)
if(NOT "input" MATCHES "^\\.")
  cmake_path(APPEND_STRING path ".")
endif()
cmake_path(APPEND_STRING path "input")

Generation

cmake_path(NORMAL_PATH <path-var> [OUTPUT_VARIABLE <out-var>])

Normalize <path-var> according the steps described in Normalization.

cmake_path(RELATIVE_PATH <path-var> [BASE_DIRECTORY <input>]
                                    [OUTPUT_VARIABLE <out-var>])

Modifies <path-var> to make it relative to the BASE_DIRECTORY argument. If BASE_DIRECTORY is not specified, the default base directory will be CMAKE_CURRENT_SOURCE_DIR.

For reference, the algorithm used to compute the relative path is the same as that used by C++ std::filesystem::path::lexically_relative.

cmake_path(ABSOLUTE_PATH <path-var> [BASE_DIRECTORY <input>] [NORMALIZE]
                                    [OUTPUT_VARIABLE <out-var>])

If <path-var> is a relative path (IS_RELATIVE is true), it is evaluated relative to the given base directory specified by BASE_DIRECTORY option. If BASE_DIRECTORY is not specified, the default base directory will be CMAKE_CURRENT_SOURCE_DIR.

When the NORMALIZE option is specified, the path is normalized after the path computation.

Because cmake_path() does not access the filesystem, symbolic links are not resolved. To compute a real path with symbolic links resolved, use the file(REAL_PATH) command instead.

Native Conversion

For commands in this section, native refers to the host platform, not the target platform when cross-compiling.

cmake_path(NATIVE_PATH <path-var> [NORMALIZE] <out-var>)

Converts a cmake-style <path-var> into a native path with platform-specific slashes (\ on Windows hosts and / elsewhere).

When the NORMALIZE option is specified, the path is normalized before the conversion.

cmake_path(CONVERT <input> TO_CMAKE_PATH_LIST <out-var> [NORMALIZE])

Converts a native <input> path into a cmake-style path with forward slashes (/). On Windows hosts, the long filename marker is taken into account. The input can be a single path or a system search path like $ENV{PATH}. A search path will be converted to a cmake-style list separated by ; characters (on non-Windows platforms, this essentially means : separators are replaced with ;). The result of the conversion is stored in the <out-var> variable.

When the NORMALIZE option is specified, the path is normalized before the conversion.

Note

Unlike most other cmake_path() subcommands, the CONVERT subcommand takes a literal string as input, not the name of a variable.

cmake_path(CONVERT <input> TO_NATIVE_PATH_LIST <out-var> [NORMALIZE])

Converts a cmake-style <input> path into a native path with platform-specific slashes (\ on Windows hosts and / elsewhere). The input can be a single path or a cmake-style list. A list will be converted into a native search path (;-separated on Windows, :-separated on other platforms). The result of the conversion is stored in the <out-var> variable.

When the NORMALIZE option is specified, the path is normalized before the conversion.

Note

Unlike most other cmake_path() subcommands, the CONVERT subcommand takes a literal string as input, not the name of a variable.

For example:

set(paths "/a/b/c" "/x/y/z")
cmake_path(CONVERT "${paths}" TO_NATIVE_PATH_LIST native_paths)
message("Native path list is \"${native_paths}\"")

Output on Windows:

Native path list is "\a\b\c;\x\y\z"

Output on all other platforms:

Native path list is "/a/b/c:/x/y/z"

Hashing

cmake_path(HASH <path-var> <out-var>)

Compute a hash value of <path-var> such that for two paths p1 and p2 that compare equal (COMPARE ... EQUAL), the hash value of p1 is equal to the hash value of p2. The path is always normalized before the hash is computed.