Create custom targets to build projects in external trees


The ExternalProject_Add function creates a custom target to drive download, update/patch, configure, build, install and test steps of an external project:

ExternalProject_Add(<name> [<option>...])

General options are:

DEPENDS <projects>...

Targets on which the project depends

PREFIX <dir>

Root dir for entire project


Sep to be replaced by ; in cmd lines

TMP_DIR <dir>

Directory to store temporary files


Directory to store step timestamps


The “all” target does not depend on this

Download step options are:


File name to store (if not end of URL)


Directory to store downloaded files


Command to download source tree


Disable download progress reports


CVSROOT of CVS repository


Module to checkout from CVS repo

CVS_TAG <tag>

Tag to checkout from CVS repo


URL of Subversion repo


Revision to checkout from Subversion repo

SVN_USERNAME <username>

Username for Subversion checkout and update

SVN_PASSWORD <password>

Password for Subversion checkout and update


Trust the Subversion server site certificate


URL of git repo

GIT_TAG <tag>

Git branch name, commit id or tag

GIT_SUBMODULES <module>...

Git submodules that shall be updated, all if empty


URL of mercurial repo

HG_TAG <tag>

Mercurial branch name, commit id or tag

URL /.../src.tgz

Full path or URL of source


Hash of file at URL

URL_MD5 md5

Equivalent to URL_HASH MD5=md5


Should certificate for https be checked


Path to a certificate authority file

TIMEOUT <seconds>

Time allowed for file download operations

Update/Patch step options are:


Source work-tree update command


Never update automatically from the remote repository


Command to patch downloaded source

Configure step options are:


Source dir to be used for build


Build tree configuration command

CMAKE_COMMAND /.../cmake

Specify alternative cmake executable


Specify generator for native build


Generator-specific platform name


Generator-specific toolset name

CMAKE_ARGS <arg>...

Arguments to CMake command line. These arguments are passed to CMake command line, and can contain arguments other than cache values, see also CMake Options. Arguments in the form -Dvar:string=on are always passed to the command line, and therefore cannot be changed by the user.


Initial cache arguments, of the form -Dvar:string=on. These arguments are written in a pre-load a script that populates CMake cache, see also cmake -C. This allows to overcome command line length limits. These arguments are set() using the FORCE argument, and therefore cannot be changed by the user.


Initial default cache arguments, of the form -Dvar:string=on. These arguments are written in a pre-load a script that populates CMake cache, see also cmake -C. This allows to overcome command line length limits. These arguments can be used as default value that will be set if no previous value is found in the cache, and that the user can change later.

Build step options are:


Specify build dir location


Command to drive the native build


Use source dir for build dir


No stamp file, build step always runs


Files that will be generated by the build command but may or may not have their modification time updated by subsequent builds.

Install step options are:


Installation prefix


Command to drive install after build

Test step options are:


Add test step executed before install step


Add test step executed after install step


Main target does not depend on the test step


Command to drive test

Output logging options are:


Wrap download in script to log output


Wrap update in script to log output


Wrap configure in script to log output


Wrap build in script to log output


Wrap test in script to log output


Wrap install in script to log output

Other options are:

STEP_TARGETS <step-target>...

Generate custom targets for these steps


Generate custom targets for these steps that do not depend on other external projects even if a dependency is set

The *_DIR options specify directories for the project, with default directories computed as follows. If the PREFIX option is given to ExternalProject_Add() or the EP_PREFIX directory property is set, then an external project is built and installed under the specified prefix:

TMP_DIR      = <prefix>/tmp
STAMP_DIR    = <prefix>/src/<name>-stamp
DOWNLOAD_DIR = <prefix>/src
SOURCE_DIR   = <prefix>/src/<name>
BINARY_DIR   = <prefix>/src/<name>-build
INSTALL_DIR  = <prefix>

Otherwise, if the EP_BASE directory property is set then components of an external project are stored under the specified base:

TMP_DIR      = <base>/tmp/<name>
STAMP_DIR    = <base>/Stamp/<name>
DOWNLOAD_DIR = <base>/Download/<name>
SOURCE_DIR   = <base>/Source/<name>
BINARY_DIR   = <base>/Build/<name>
INSTALL_DIR  = <base>/Install/<name>

If no PREFIX, EP_PREFIX, or EP_BASE is specified then the default is to set PREFIX to <name>-prefix. Relative paths are interpreted with respect to the build directory corresponding to the source directory in which ExternalProject_Add is invoked.

If SOURCE_DIR is explicitly set to an existing directory the project will be built from it. Otherwise a download step must be specified using one of the DOWNLOAD_COMMAND, CVS_*, SVN_*, or URL options. The URL option may refer locally to a directory or source tarball, or refer to a remote tarball (e.g. http://.../src.tgz).

If UPDATE_DISCONNECTED is set, the update step is not executed automatically when building the main target. The update step can still be added as a step target and called manually. This is useful if you want to allow to build the project when you are disconnected from the network (you might still need the network for the download step). This is disabled by default. The directory property EP_UPDATE_DISCONNECTED can be used to change the default value for all the external projects in the current directory and its subdirectories.


The ExternalProject_Add_Step function adds a custom step to an external project:

ExternalProject_Add_Step(<name> <step> [<option>...])

Options are:

COMMAND <cmd>...

Command line invoked by this step

COMMENT "<text>..."

Text printed when step executes

DEPENDEES <step>...

Steps on which this step depends

DEPENDERS <step>...

Steps that depend on this step

DEPENDS <file>...

Files on which this step depends

BYPRODUCTS <file>...

Files that will be generated by this step but may or may not have their modification time updated by subsequent builds.


No stamp file, step always runs


Main target does not depend on this step


Working directory for command


Wrap step in script to log output

The command line, comment, and working directory of every standard and custom step is processed to replace tokens <SOURCE_DIR>, <BINARY_DIR>, <INSTALL_DIR>, and <TMP_DIR> with corresponding property values.

Any builtin step that specifies a <step>_COMMAND cmd... or custom step that specifies a COMMAND cmd... may specify additional command lines using the form COMMAND cmd.... At build time the commands will be executed in order and aborted if any one fails. For example:

... BUILD_COMMAND make COMMAND echo done ...

specifies to run make and then echo done during the build step. Whether the current working directory is preserved between commands is not defined. Behavior of shell operators like && is not defined.


The ExternalProject_Get_Property function retrieves external project target properties:

ExternalProject_Get_Property(<name> [prop1 [prop2 [...]]])

It stores property values in variables of the same name. Property names correspond to the keyword argument names of ExternalProject_Add.


The ExternalProject_Add_StepTargets function generates custom targets for the steps listed:

ExternalProject_Add_StepTargets(<name> [NO_DEPENDS] [step1 [step2 [...]]])

If NO_DEPENDS is set, the target will not depend on the dependencies of the complete project. This is usually safe to use for the download, update, and patch steps that do not require that all the dependencies are updated and built. Using NO_DEPENDS for other of the default steps might break parallel builds, so you should avoid, it. For custom steps, you should consider whether or not the custom commands requires that the dependencies are configured, built and installed.

If STEP_TARGETS or INDEPENDENT_STEP_TARGETS is set then ExternalProject_Add_StepTargets is automatically called at the end of matching calls to ExternalProject_Add_Step. Pass STEP_TARGETS or INDEPENDENT_STEP_TARGETS explicitly to individual ExternalProject_Add calls, or implicitly to all ExternalProject_Add calls by setting the directory properties EP_STEP_TARGETS and EP_INDEPENDENT_STEP_TARGETS. The INDEPENDENT version of the argument and of the property will call ExternalProject_Add_StepTargets with the NO_DEPENDS argument.

If STEP_TARGETS and INDEPENDENT_STEP_TARGETS are not set, clients may still manually call ExternalProject_Add_StepTargets after calling ExternalProject_Add or ExternalProject_Add_Step.

This functionality is provided to make it easy to drive the steps independently of each other by specifying targets on build command lines. For example, you may be submitting to a sub-project based dashboard, where you want to drive the configure portion of the build, then submit to the dashboard, followed by the build portion, followed by tests. If you invoke a custom target that depends on a step halfway through the step dependency chain, then all the previous steps will also run to ensure everything is up to date.

For example, to drive configure, build and test steps independently for each ExternalProject_Add call in your project, write the following line prior to any ExternalProject_Add calls in your CMakeLists.txt file:

set_property(DIRECTORY PROPERTY EP_STEP_TARGETS configure build test)

The ExternalProject_Add_StepDependencies function add some dependencies for some external project step:

ExternalProject_Add_StepDependencies(<name> <step> [target1 [target2 [...]]])

This function takes care to set both target and file level dependencies, and will ensure that parallel builds will not break. It should be used instead of add_dependencies() when adding a dependency for some of the step targets generated by ExternalProject.