add_custom_command¶
Add a custom build rule to the generated build system.
There are two main signatures for add_custom_command
.
Generating Files¶
The first signature is for adding a custom command to produce an output:
add_custom_command(OUTPUT output1 [output2 ...]
COMMAND command1 [ARGS] [args1...]
[COMMAND command2 [ARGS] [args2...] ...]
[MAIN_DEPENDENCY depend]
[DEPENDS [depends...]]
[BYPRODUCTS [files...]]
[IMPLICIT_DEPENDS <lang1> depend1
[<lang2> depend2] ...]
[WORKING_DIRECTORY dir]
[COMMENT comment]
[DEPFILE depfile]
[JOB_POOL job_pool]
[JOB_SERVER_AWARE <bool>]
[VERBATIM] [APPEND] [USES_TERMINAL]
[CODEGEN]
[COMMAND_EXPAND_LISTS]
[DEPENDS_EXPLICIT_ONLY])
This defines a command to generate specified OUTPUT
file(s).
A target created in the same directory (CMakeLists.txt
file)
that specifies any output of the custom command as a source file
is given a rule to generate the file using the command at build time.
Do not list the output in more than one independent target that
may build in parallel or the instances of the rule may conflict.
Instead, use the add_custom_target()
command to drive the
command and make the other targets depend on that one. See the
Example: Generating Files for Multiple Targets below.
The options are:
APPEND
Append the
COMMAND
andDEPENDS
option values to the custom command for the first output specified. There must have already been a previous call to this command with the same output.If the previous call specified the output via a generator expression, the output specified by the current call must match in at least one configuration after evaluating generator expressions. In this case, the appended commands and dependencies apply to all configurations.
The
COMMENT
,MAIN_DEPENDENCY
, andWORKING_DIRECTORY
options are currently ignored when APPEND is given, but may be used in the future.BYPRODUCTS
New in version 3.2.
Specify the files the command is expected to produce but whose modification time may or may not be newer than the dependencies. If a byproduct name is a relative path it will be interpreted relative to the build tree directory corresponding to the current source directory. Each byproduct file will be marked with the
GENERATED
source file property automatically.See policy
CMP0058
for the motivation behind this feature.Explicit specification of byproducts is supported by the
Ninja
generator to tell theninja
build tool how to regenerate byproducts when they are missing. It is also useful when other build rules (e.g. custom commands) depend on the byproducts. Ninja requires a build rule for any generated file on which another rule depends even if there are order-only dependencies to ensure the byproducts will be available before their dependents build.The Makefile Generators will remove
BYPRODUCTS
and otherGENERATED
files duringmake clean
.New in version 3.20: Arguments to
BYPRODUCTS
may use a restricted set ofgenerator expressions
. Target-dependent expressions are not permitted.COMMAND
Specify the command-line(s) to execute at build time. If more than one
COMMAND
is specified they will be executed in order, but not necessarily composed into a stateful shell or batch script. (To run a full script, use theconfigure_file()
command or thefile(GENERATE)
command to create it, and then specify aCOMMAND
to launch it.) The optionalARGS
argument is for backward compatibility and will be ignored.If
COMMAND
specifies an executable target name (created by theadd_executable()
command), it will automatically be replaced by the location of the executable created at build time if either of the following is true:The target is not being cross-compiled (i.e. the
CMAKE_CROSSCOMPILING
variable is not set to true).New in version 3.6: The target is being cross-compiled and an emulator is provided (i.e. its
CROSSCOMPILING_EMULATOR
target property is set). In this case, the contents ofCROSSCOMPILING_EMULATOR
will be prepended to the command before the location of the target executable.
If neither of the above conditions are met, it is assumed that the command name is a program to be found on the
PATH
at build time.Arguments to
COMMAND
may usegenerator expressions
. Use theTARGET_FILE
generator expression to refer to the location of a target later in the command line (i.e. as a command argument rather than as the command to execute).Whenever one of the following target based generator expressions are used as a command to execute or is mentioned in a command argument, a target-level dependency will be added automatically so that the mentioned target will be built before any target using this custom command (see policy
CMP0112
).TARGET_FILE
TARGET_LINKER_FILE
TARGET_SONAME_FILE
TARGET_PDB_FILE
This target-level dependency does NOT add a file-level dependency that would cause the custom command to re-run whenever the executable is recompiled. List target names with the
DEPENDS
option to add such file-level dependencies.COMMENT
Display the given message before the commands are executed at build time.
New in version 3.26: Arguments to
COMMENT
may usegenerator expressions
.DEPENDS
Specify files on which the command depends. Each argument is converted to a dependency as follows:
If the argument is the name of a target (created by the
add_custom_target()
,add_executable()
, oradd_library()
command) a target-level dependency is created to make sure the target is built before any target using this custom command. Additionally, if the target is an executable or library, a file-level dependency is created to cause the custom command to re-run whenever the target is recompiled.If the argument is an absolute path, a file-level dependency is created on that path.
If the argument is the name of a source file that has been added to a target or on which a source file property has been set, a file-level dependency is created on that source file.
If the argument is a relative path and it exists in the current source directory, a file-level dependency is created on that file in the current source directory.
Otherwise, a file-level dependency is created on that path relative to the current binary directory.
If any dependency is an
OUTPUT
of another custom command in the same directory (CMakeLists.txt
file), CMake automatically brings the other custom command into the target in which this command is built.New in version 3.16: A target-level dependency is added if any dependency is listed as
BYPRODUCTS
of a target or any of its build events in the same directory to ensure the byproducts will be available.If
DEPENDS
is not specified, the command will run whenever theOUTPUT
is missing; if the command does not actually create theOUTPUT
, the rule will always run.New in version 3.1: Arguments to
DEPENDS
may usegenerator expressions
.COMMAND_EXPAND_LISTS
New in version 3.8.
Lists in
COMMAND
arguments will be expanded, including those created withgenerator expressions
, allowingCOMMAND
arguments such as${CC} "-I$<JOIN:$<TARGET_PROPERTY:foo,INCLUDE_DIRECTORIES>,;-I>" foo.cc
to be properly expanded.CODEGEN
New in version 3.31.
Adds the custom command to a global
codegen
target that can be used to execute the custom command while avoiding the majority of the build graph.This option is supported only by Ninja Generators and Makefile Generators, and is ignored by other generators. Furthermore, this option is allowed only if policy
CMP0171
is set toNEW
.IMPLICIT_DEPENDS
Request scanning of implicit dependencies of an input file. The language given specifies the programming language whose corresponding dependency scanner should be used. Currently only
C
andCXX
language scanners are supported. The language has to be specified for every file in theIMPLICIT_DEPENDS
list. Dependencies discovered from the scanning are added to those of the custom command at build time. Note that theIMPLICIT_DEPENDS
option is currently supported only for Makefile generators and will be ignored by other generators.Note
This option cannot be specified at the same time as
DEPFILE
option.JOB_POOL
New in version 3.15.
Specify a
pool
for theNinja
generator. Incompatible withUSES_TERMINAL
, which implies theconsole
pool. Using a pool that is not defined byJOB_POOLS
causes an error by ninja at build time.JOB_SERVER_AWARE
New in version 3.28.
Specify that the command is GNU Make job server aware.
For the
Unix Makefiles
,MSYS Makefiles
, andMinGW Makefiles
generators this will add the+
prefix to the recipe line. See the GNU Make Documentation for more information.This option is silently ignored by other generators.
MAIN_DEPENDENCY
Specify the primary input source file to the command. This is treated just like any value given to the
DEPENDS
option but also suggests to Visual Studio generators where to hang the custom command. Each source file may have at most one command specifying it as its main dependency. A compile command (i.e. for a library or an executable) counts as an implicit main dependency which gets silently overwritten by a custom command specification.OUTPUT
Specify the output files the command is expected to produce. Each output file will be marked with the
GENERATED
source file property automatically. If the output of the custom command is not actually created as a file on disk it should be marked with theSYMBOLIC
source file property.If an output file name is a relative path, its absolute path is determined by interpreting it relative to:
the build directory corresponding to the current source directory (
CMAKE_CURRENT_BINARY_DIR
), orthe current source directory (
CMAKE_CURRENT_SOURCE_DIR
).
The path in the build directory is preferred unless the path in the source tree is mentioned as an absolute source file path elsewhere in the current directory.
The output file path may not contain
<
or>
characters.New in version 3.20: Arguments to
OUTPUT
may use a restricted set ofgenerator expressions
. Target-dependent expressions are not permitted.Changed in version 3.28: In targets using File Sets, custom command outputs are now considered private unless they are listed in a non-private file set. See policy
CMP0154
.Changed in version 3.30: The output file path may now use
#
characters, except when using theBorland Makefiles
generator.USES_TERMINAL
New in version 3.2.
The command will be given direct access to the terminal if possible. With the
Ninja
generator, this places the command in theconsole
pool
.VERBATIM
All arguments to the commands will be escaped properly for the build tool so that the invoked command receives each argument unchanged. Note that one level of escapes is still used by the CMake language processor before add_custom_command even sees the arguments. Use of
VERBATIM
is recommended as it enables correct behavior. WhenVERBATIM
is not given the behavior is platform specific because there is no protection of tool-specific special characters.WORKING_DIRECTORY
Execute the command with the given current working directory. If it is a relative path it will be interpreted relative to the build tree directory corresponding to the current source directory.
New in version 3.13: Arguments to
WORKING_DIRECTORY
may usegenerator expressions
.DEPFILE
New in version 3.7.
Specify a depfile which holds dependencies for the custom command. It is usually emitted by the custom command itself. This keyword may only be used if the generator supports it, as detailed below.
The expected format, compatible with what is generated by
gcc
with the option-M
, is independent of the generator or platform.The formal syntax, as specified using BNF notation with the regular extensions, is the following:
depfile ::=
rule
* rule ::=targets
(':' (separator
dependencies
?)?)?eol
targets ::=target
(separator
target
)*separator
* target ::=pathname
dependencies ::=dependency
(separator
dependency
)*separator
* dependency ::=pathname
separator ::= (space
|line_continue
)+ line_continue ::= '\'eol
space ::= ' ' | '\t' pathname ::=character
+ character ::=std_character
|dollar
|hash
|whitespace
std_character ::= <any character except '$', '#' or ' '> dollar ::= '$$' hash ::= '\#' whitespace ::= '\ ' eol ::= '\r'? '\n'Note
As part of
pathname
, any slash and backslash is interpreted as a directory separator.New in version 3.7: The
Ninja
generator supportsDEPFILE
since the keyword was first added.New in version 3.17: Added the
Ninja Multi-Config
generator, which included support for theDEPFILE
keyword.New in version 3.20: Added support for Makefile Generators.
Note
DEPFILE
cannot be specified at the same time as theIMPLICIT_DEPENDS
option for Makefile Generators.New in version 3.21: Added support for Visual Studio Generators with VS 2012 and above, and for the
Xcode
generator. Support forgenerator expressions
was also added.New in version 3.29: The Ninja Generators will now incorporate the dependencies into its "deps log" database if the file is not listed in
OUTPUTS
orBYPRODUCTS
.Using
DEPFILE
with generators other than those listed above is an error.If the
DEPFILE
argument is relative, it should be relative toCMAKE_CURRENT_BINARY_DIR
, and any relative paths inside theDEPFILE
should also be relative toCMAKE_CURRENT_BINARY_DIR
. See policyCMP0116
, which is alwaysNEW
for Makefile Generators, Visual Studio Generators, and theXcode
generator.
DEPENDS_EXPLICIT_ONLY
New in version 3.27.
Indicates that the command's
DEPENDS
argument represents all files required by the command and implicit dependencies are not required.Without this option, if any target uses the output of the custom command, CMake will consider that target's dependencies as implicit dependencies for the custom command in case this custom command requires files implicitly created by those targets.
This option can be enabled on all custom commands by setting
CMAKE_ADD_CUSTOM_COMMAND_DEPENDS_EXPLICIT_ONLY
toON
.Only the Ninja Generators actually use this information to remove unnecessary implicit dependencies.
See also the
OPTIMIZE_DEPENDENCIES
target property, which may provide another way for reducing the impact of target dependencies in some scenarios.
Examples: Generating Files¶
Custom commands may be used to generate source files. For example, the code:
add_custom_command(
OUTPUT out.c
COMMAND someTool -i ${CMAKE_CURRENT_SOURCE_DIR}/in.txt
-o out.c
DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/in.txt
VERBATIM)
add_library(myLib out.c)
adds a custom command to run someTool
to generate out.c
and then
compile the generated source as part of a library. The generation rule
will re-run whenever in.txt
changes.
New in version 3.20: One may use generator expressions to specify per-configuration outputs. For example, the code:
add_custom_command(
OUTPUT "out-$<CONFIG>.c"
COMMAND someTool -i ${CMAKE_CURRENT_SOURCE_DIR}/in.txt
-o "out-$<CONFIG>.c"
-c "$<CONFIG>"
DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/in.txt
VERBATIM)
add_library(myLib "out-$<CONFIG>.c")
adds a custom command to run someTool
to generate out-<config>.c
,
where <config>
is the build configuration, and then compile the generated
source as part of a library.
New in version 3.31: Use the CODEGEN
option to add a custom command's outputs to the builtin
codegen
target. This is useful to make generated code available for
static analysis without building the entire project. For example:
add_executable(someTool someTool.c)
add_custom_command(
OUTPUT out.c
COMMAND someTool -o out.c
CODEGEN)
add_library(myLib out.c)
A user may build the codegen
target to generate out.c
.
someTool
is built as dependency, but myLib
is not built at all.
Example: Generating Files for Multiple Targets¶
If multiple independent targets need the same custom command output, it must be attached to a single custom target on which they all depend. Consider the following example:
add_custom_command(
OUTPUT table.csv
COMMAND makeTable -i ${CMAKE_CURRENT_SOURCE_DIR}/input.dat
-o table.csv
DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/input.dat
VERBATIM)
add_custom_target(generate_table_csv DEPENDS table.csv)
add_custom_command(
OUTPUT foo.cxx
COMMAND genFromTable -i table.csv -case foo -o foo.cxx
DEPENDS table.csv # file-level dependency
generate_table_csv # target-level dependency
VERBATIM)
add_library(foo foo.cxx)
add_custom_command(
OUTPUT bar.cxx
COMMAND genFromTable -i table.csv -case bar -o bar.cxx
DEPENDS table.csv # file-level dependency
generate_table_csv # target-level dependency
VERBATIM)
add_library(bar bar.cxx)
Output foo.cxx
is needed only by target foo
and output bar.cxx
is needed only by target bar
, but both targets need table.csv
,
transitively. Since foo
and bar
are independent targets that may
build concurrently, we prevent them from racing to generate table.csv
by placing its custom command in a separate target, generate_table_csv
.
The custom commands generating foo.cxx
and bar.cxx
each specify a
target-level dependency on generate_table_csv
, so the targets using them,
foo
and bar
, will not build until after target generate_table_csv
is built.
Build Events¶
The second signature adds a custom command to a target such as a library or executable. This is useful for performing an operation before or after building the target. The command becomes part of the target and will only execute when the target itself is built. If the target is already built, the command will not execute.
add_custom_command(TARGET <target>
PRE_BUILD | PRE_LINK | POST_BUILD
COMMAND command1 [ARGS] [args1...]
[COMMAND command2 [ARGS] [args2...] ...]
[BYPRODUCTS [files...]]
[WORKING_DIRECTORY dir]
[COMMENT comment]
[VERBATIM]
[COMMAND_EXPAND_LISTS])
This defines a new command that will be associated with building the
specified <target>
. The <target>
must be defined in the current
directory; targets defined in other directories may not be specified.
When the command will happen is determined by which of the following is specified:
PRE_BUILD
This option has unique behavior for the Visual Studio Generators. When using one of the Visual Studio generators, the command will run before any other rules are executed within the target. With all other generators, this option behaves the same as
PRE_LINK
instead. Because of this, it is recommended to avoid usingPRE_BUILD
except when it is known that a Visual Studio generator is being used.PRE_LINK
Run after sources have been compiled but before linking the binary or running the librarian or archiver tool of a static library. This is not defined for targets created by the
add_custom_target()
command.POST_BUILD
Run after all other rules within the target have been executed.
Projects should always specify one of the above three keywords when using
the TARGET
form. For backward compatibility reasons, POST_BUILD
is
assumed if no such keyword is given, but projects should explicitly provide
one of the keywords to make clear the behavior they expect.
Note
Because generator expressions can be used in custom commands,
it is possible to define COMMAND
lines or whole custom commands
which evaluate to empty strings for certain configurations.
For Visual Studio Generators these command
lines or custom commands will be omitted for the specific
configuration and no "empty-string-command" will be added.
This allows adding individual build events for every configuration.
New in version 3.21: Support for target-dependent generator expressions.
New in version 3.29: The <target>
may be an ALIAS target.
Examples: Build Events¶
A POST_BUILD
event may be used to post-process a binary after linking.
For example, the code:
add_executable(myExe myExe.c)
add_custom_command(
TARGET myExe POST_BUILD
COMMAND someHasher -i "$<TARGET_FILE:myExe>"
-o "$<TARGET_FILE:myExe>.hash"
VERBATIM)
will run someHasher
to produce a .hash
file next to the executable
after linking.
New in version 3.20: One may use generator expressions to specify per-configuration byproducts. For example, the code:
add_library(myPlugin MODULE myPlugin.c)
add_custom_command(
TARGET myPlugin POST_BUILD
COMMAND someHasher -i "$<TARGET_FILE:myPlugin>"
--as-code "myPlugin-hash-$<CONFIG>.c"
BYPRODUCTS "myPlugin-hash-$<CONFIG>.c"
VERBATIM)
add_executable(myExe myExe.c "myPlugin-hash-$<CONFIG>.c")
will run someHasher
after linking myPlugin
, e.g. to produce a .c
file containing code to check the hash of myPlugin
that the myExe
executable can use to verify it before loading.
Ninja Multi-Config¶
New in version 3.20: add_custom_command
supports the Ninja Multi-Config
generator's cross-config capabilities. See the generator documentation
for more information.