Buck: genrule()

genrule()

A genrule() is used to generate files from a shell command. It must produce a single output file or folder.

Arguments

  • name (required) #

    The name of the genrule.

  • srcs (defaults to []) #

    A list of files to be used in the shell command.

  • cmd (defaults to None) #

    The shell command to run to generate the output file. It is the fallback of bash and cmd_exe. It will be subject to the following environment variable substitutions:

    SRCS
    A space-delimited string expansion of the srcs argument where each element of srcs will be translated into an absolute path.
    SRCDIR
    The absolute path to a directory to which sources are copied to prior to running the command.
    OUT
    The output file for the genrule(). The file specified by this variable must always be written by this command. If not, the execution of this rule will be considered a failure, halting the build process.
    It is also possible to expand references to other rules within the cmd, using builtin string parameter macros. This expansion takes two supported forms:
    $(classpath /F;path/to:target)
    Expands a build rule for something that has a java classpath to the transitive classpath of that rule. If the rule does not have (or contribute to) a classpath, an exception will be thrown and the build will break.
    $(exe //path/to:target)
    Expands a build rule that results in an executable to the commands necessary to execute that command. For example, a java_binary() may expand to a call to java -jar path/to/target.jar. Files that are executable (perhaps generated by a genrule()) will also be expanded. If the build rule does not generate an executable output an exception will be thrown and the build will break.
    $(location //path/to:target)
    Expands to the location of the output of the build rule. This means that you can refer to these without needing to be aware of how Buck is storing data on the disk mid-build.
    $(maven_coords //path/to:target)
    Expands to the Maven coordinates for the build rule. This allows you to access the Maven coordinates for Maven-aware build rules. The format of the expansion is: <groupId>:<artifactId>[:<extension>[:<classifier>]]:<version>
    Note that all build rules expanded in the command will be automatically considered to be dependencies of the genrule().

  • bash (defaults to None) #

    The platform-specific version of parameter cmd. It runs on UNIX in which bash is installed and has a higher priority than cmd. Command specified will be run with /bin/bash -c.

  • cmd_exe (defaults to None) #

    The platform-specific version of parameter cmd. It runs on Windows and has a higher priority than cmd. Command specified will be run with cmd.exe /c.

  • type (defaults to None) #

    The type of this genrule. This is used for logging and is particularly useful for grouping different genrules that share an underlying logical "type".

  • out (required) #

    The name of the output file or directory. Must be unique within the build file in which the genrule() is declared.

  • executable (defaults to False) #

    Whether the output of the genrule is itself executable. Marking an output as executable makes buck run and $(exe ...) macro expansion work with this target.

  • tests (defaults to []) #

    List of build targets that identify the test rules that exercise this target.

  • visibility (defaults to []) #

    List of build target patterns that identify the build rules that can include this rule in its deps.

  • licenses (defaults to []) #

    Set of license files for this library. To get the list of license files for a given build rule and all of its dependencies, you can use buck query.

  • labels (defaults to []) #

    Set of arbitrary strings which allow you to annotate a build rule with tags that can be searched for over an entire dependency tree using buck query attrfilter.

Examples

This genrule() uses a Python script to derive a new AndroidManifest.xml from an AndroidManifest.xml in the source tree. Note you don't need to prepend execution commands with python: Buck knows how to execute different kinds of binaries using $(exe) command.
genrule(
  name = 'generate_manifest',
  srcs = [
    'AndroidManifest.xml',
  ],
  bash = '$(exe //python/android:basic_to_full) ' \
      '$SRCDIR/AndroidManifest.xml > $OUT',
  cmd_exe = '$(exe //python/android:basic_to_full) ' \
      '%SRCDIR%\\AndroidManifest.xml > %OUT%',
  out = 'AndroidManifest.xml',
)