Buck: buck build
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buck build

Builds one or more rules specified by a set of build targets and build target patterns. This is the most commonly used command in Buck.


buck build { <build target> | <build target pattern> } . . .


buck build //java/com/example/app:amazing

Note that any remote_file rules referenced by your build rules must be downloaded with buck fetch prior to calling this command unless you set in_build = true in the [download] section of your .buckconfig.


  • --build-report Specifies a file where a JSON summary of the build output should be written. Note that --build-report can be used without --keep-going, though if --keep-going is not specified, the generated report may be partial and not include information about the targets that buck haven't had a chance to try to build. Here is a sample build report:

      "success": false,
      "results": {
        "//fake:rule1": {
          "success": true,
          "type": "BUILT_LOCALLY",
          "output": "buck-out/gen/fake/rule1.txt"
        "//fake:rule2": {
          "success": false
        "//fake:rule3": {
          "success": true,
          "type": "FETCHED_FROM_CACHE"

    In this example, both //fake:rule1 and //fake:rule3 were built successfully, but only //fake:rule1 had an output file associated with the rule.

    Note that this contains the same information that --keep-going prints to the console, but is easier to parse programmatically. This report may contain more fields in the future.

  • --keep-going When specified, Buck will attempt to build all targets specified on the command line, even if some of the targets fail. (Buck's default behavior is to exit immediately when any of the specified targets fail.)

    When --keep-going is specified, a report of the build will be printed to stderr, detailing the build status of each target. Each line of the report represents the status of one build target, which has up to four columns:

    1. OK or FAIL, as per the success of the build rule.
    2. The build target of the rule.
    3. If successful, the type of the success as defined by the com.facebook.buck.core.build.engine.BuildRuleSuccessType enum.
    4. If successful, the path to the output file of the rule, if it exists.
    For example, if Buck were run with the following arguments:

    buck build --keep-going //fake:rule1 //fake:rule2 //fake:rule3

    Then the report printed to stderr might look like:

    OK   //fake:rule1 BUILT_LOCALLY buck-out/gen/fake/rule1.txt
    FAIL //fake:rule2
    OK   //fake:rule3 FETCHED_FROM_CACHE

    In this example, both //fake:rule1 and //fake:rule3 were built successfully, but only //fake:rule1 had an output file associated with the rule. Admittedly, the state of column 1 could be derived from the presence of column 3, but the encoding of column 1 makes it easier to filter out successful rules from failed ones.

    Note that when --keep-going is specified, the exit code will be 0 only if all targets were built successfully.

    This option is analogous to -k/--keep-going in Make.

  • --out Takes the output of the build target and copies it to the specified path. Only works with a single build target, and the corresponding build rule must support this option.
  • --populate-cache Performs a cache population, which makes the output of all unchanged transitive dependencies available (if these outputs are available in the remote cache). Does not build changed or unavailable dependencies locally.
  • --show-output

    Print the relative paths to the output for each target after the target name. Note that some rules—such as genrule—generate sources instead of build artifacts.

    Additional Parameters

    For additional parameters that are available with this command, see the Common Parameters topic.


View compiler flags using the compilation database

For C++ builds, to view the compiler flags that Buck is passing to the C++ compiler, tell Buck to generate a compilation database for the target. The compilation database is a JSON file that contains information about how Buck compiled the target. The syntax is:

buck build path/to/target#compilation-database

You can then get the path to the compilation-database file itself using:

buck targets --show-output path/to/target#compilation-database

For example:

$ buck clean
Parsing buck files: finished in 1.7 sec (100%)
Building: finished in 1.5 sec (100%) 3/3 jobs, 3 updated, 0.0% cache miss
  Total time: 3.7 sec

$ buck build :main#compilation-database
Building: finished in 1.5 sec (100%) 3/3 jobs, 3 updated, 0.0% cache miss
  Total time: 3.7 sec

$ buck targets --show-output :main#compilation-database
//:main#compilation-database buck-out/gen/__main#compilation-database/compile_commands.json

$ jq . buck-out/gen/__main#compilation-database/compile_commands.json 
    "directory": "/Users/devuser/git/gtDev/C++/oop/simple-classes",
    "file": "/Users/devuser/git/gtDev/C++/oop/simple-classes/main.cpp",
    "arguments": [

In the preceding example :main specifies a relative build target that is defined in the build file located in the current directory. The jq tool—available through package managers such as Homebrew—enables you to pretty-print JSON files.