GN(1)

🦋 GN(1) — User Commands, but make it a group chat 🦋

okay so this is the gn manual page, filed under User Commands in section 1, and bestie it is long. like, "grab a snack" long. 🍓

the good news? you never have to memorize any of this, because everything on this page has its own little help page. type:

gn help <command>

for commands, gn help <function> for target declarations and buildfile functions, and gn help <variable> for variables. iykyk 💅

---

✨ NAME ✨

gn — Documentation for GN

---

🎀 DESCRIPTION 🎀

this whole section is literally just the index of everything gn can do, so let's go section by section, no skipping. 🌸

💅 Commands 💅

type gn help <command> for more help on any of these, bestie. here's the whole squad:

• analyze — works out which targets are affected by a list of files. detective mode, no cap 🔍
• args — shows you the arguments your build declares, or configures them for you. yes, you can actually set them from here.
• check — checks your header dependencies.
• clean — cleans the output directory. wipe it. self care ✨
• clean_stale — same energy, but it only cleans the stale output files out of the output directory. it's selective, we respect it.
• desc — shows a whole lot of insightful information about a target or a config. it's giving gossip column but for your build 👀
• edit — edits BUILD.gn files straight from the command line.
• format — formats .gn files. they were doing their best before, but now they're pretty.
• gen — generates ninja files. this is the main character moment 🎀
• help — "does what you think." that's the entire description. no notes, iconic.
• ls — lists matching targets.
• meta — lists target metadata collection results.
• outputs — tells you which files a source or a target make.
• path — finds the paths between two targets. connect the dots 🦋
• refs — finds stuff that references a target or a file.
• suggest — suggests fixes to the build graph based on includes. bestie advice fr fr 🫶

🧚 Target declarations 🧚

type gn help <function> for more help on any of these. these are the things you use to declare targets:

• action — declares a target that runs a script a single time. one and done.
• action_foreach — declares a target that runs a script over a set of files.
• bundle_data — [iOS/macOS] declares a target without output. yes, a target with no output. it exists, that's the vibe.
• copy — declares a target that copies files. exactly what it says 💅
• create_bundle — [iOS/macOS] builds an iOS or macOS bundle.
• executable — declares an executable target.
• generated_file — declares a generated_file target.
• group — declares a named group of targets.
• loadable_module — declares a loadable module target.
• rust_library — declares a Rust library target.
• rust_proc_macro — declares a Rust procedural macro target.
• shared_library — declares a shared library target.
• source_set — declares a source set target.
• static_library — declares a static library target.
• target — declares a target with the given programmatic type. the wildcard one, lowkey powerful.

🌈 Buildfile functions 🌈

type gn help <function> for more help. this is the function section in its full glory:

• assert — asserts that an expression is true at generation time. if it's not true, it's not happening.
• config — defines a configuration object.
• declare_args — declares build arguments.
• defined — returns whether an identifier is defined.
• exec_script — synchronously runs a script and returns the output.
• expand_directory — expands a source directory and returns files.
• filter_exclude — removes values that match a set of patterns. bye 💀
• filter_include — removes values that do not match a set of patterns. keep only the ones that match.
• filter_labels_exclude — removes labels that match a set of patterns.
• filter_labels_include — removes labels that do not match a set of patterns.
• foreach — iterates over a list.
• forward_variables_from — copies variables from a different scope.
• get_label_info — gets an attribute from a target's label.
• get_path_info — extracts parts of a file or directory name.
• get_target_outputs — [file list] gets the list of outputs from a target.
• getenv — gets an environment variable.
• import — imports a file into the current scope.
• label_matches — returns whether a label matches any of a list of patterns.
• len — returns the length of a string or a list.
• not_needed — marks variables from scope as not needed. not me ignoring my problems 🙈
• path_exists — returns whether the given path exists.
• pool — defines a pool object.
• print — prints to the console.
• print_stack_trace — prints a stack trace.
• process_file_template — does template expansion over a list of files.
• read_file — reads a file into a variable.
• rebase_path — rebases a file or directory to another location.
• set_default_toolchain — sets the default toolchain name.
• set_defaults — sets default values for a target type.
• split_list — splits a list into N different sub-lists.
• string_hash — calculates a stable hash of the given string.
• string_join — concatenates a list of strings with a separator.
• string_replace — replaces substring in the given string.
• string_split — splits string into a list of strings.
• template — defines a template rule.
• tool — specifies arguments to a toolchain tool.
• toolchain — defines a toolchain.
• write_file — writes a file to disk.

⭐ Built-in predefined variables ⭐

type gn help <variable> for more help. these ones come free with the build, no assembly required:

• current_cpu — [string] the processor architecture of the current toolchain.
• current_os — [string] the operating system of the current toolchain.
• current_toolchain — [string] label of the current toolchain.
• default_toolchain — [string] label of the default toolchain.
• generate_modulemap — [string] mode for generating modulemaps.
• gn_version — [number] the version of gn. your girl has a number 👑
• host_cpu — [string] the processor architecture that GN is running on.
• host_os — [string] the operating system that GN is running on.
• invoker — [string] the invoking scope inside a template.
• python_path — [string] absolute path of Python.
• root_build_dir — [string] directory where build commands are run.
• root_gen_dir — [string] directory for the toolchain's generated files.
• root_out_dir — [string] root directory for toolchain output files.
• target_cpu — [string] the desired cpu architecture for the build.
• target_gen_dir — [string] directory for a target's generated files.
• target_name — [string] the name of the current target.
• target_os — [string] the desired operating system for the build.
• target_out_dir — [string] directory for target output files.

💜 Variables you set in targets 💜

type gn help <variable> for more help. these are the ones you get to write, so go off:

• aliased_deps — [scope] set of crate-dependency pairs.
• all_dependent_configs — [label list] configs to be forced on dependents.
• allow_circular_includes_from — [label list] permit includes from deps.
• arflags — [string list] arguments passed to static_library archiver.
• args — [string list] arguments passed to an action.
• asmflags — [string list] flags passed to the assembler.
• assert_no_deps — [label pattern list] ensure no deps on these targets.
• bridge_header — [string] path to C/Objective-C compatibility header.
• bundle_contents_dir — expansion of {{bundle_contents_dir}} in create_bundle.
• bundle_deps_filter — [label list] a list of labels that are filtered out.
• bundle_executable_dir — expansion of {{bundle_executable_dir}} in create_bundle
• bundle_resources_dir — expansion of {{bundle_resources_dir}} in create_bundle.
• bundle_root_dir — expansion of {{bundle_root_dir}} in create_bundle.
• c_additional_outputs — [string list] additional outputs for the compiler.
• cflags — [string list] flags passed to all C compiler variants.
• cflags_c — [string list] flags passed to the C compiler.
• cflags_cc — [string list] flags passed to the C++ compiler.
• cflags_objc — [string list] flags passed to the Objective C compiler.
• cflags_objcc — [string list] flags passed to the Objective C++ compiler.
• check_includes — [boolean] controls whether a target's files are checked.
• check_includes_strict — [boolean] controls whether strict include checking is enforced. strict queen 💅
• collect_validations_metadata — [bool] collect metadata values from validations deps.
• complete_static_lib — [boolean] links all deps into a static library.
• configs — [label list] configs applying to this target or config.
• contents — contents to write to file.
• crate_name — [string] the name for the compiled crate.
• crate_root — [string] the root source file for a binary or library.
• crate_type — [string] the type of linkage to use on a shared_library.
• data — [file list] runtime data file dependencies.
• data_deps — [label list] non-linked dependencies.
• data_keys — [string list] keys from which to collect metadata.
• defines — [string list] C preprocessor defines.
• depfile — [string] file name for input dependencies for actions.
• deps — [label list] private linked dependencies.
• externs — [scope] set of Rust crate-dependency pairs.
• framework_dirs — [directory list] additional framework search directories.
• frameworks — [name list] name of frameworks that must be linked.
• friend — [label pattern list] allow targets to include private headers. friendship is a permission system 🫶
• gen_deps — [label list] declares targets that should generate when this one does.
• include_dirs — [directory list] additional include directories.
• inputs — [file list] additional compile-time dependencies.
• ldflags — [string list] flags passed to the linker.
• lib_dirs — [directory list] additional library directories.
• libs — [string list] additional libraries to link.
• metadata — [scope] metadata of this target.
• mnemonic — [string] prefix displayed when ninja runs this action.
• module_name — [string] the name for the compiled module.
• output_conversion — data format for generated_file targets.
• output_dir — [directory] directory to put output file in.
• output_extension — [string] value to use for the output's file extension.
• output_name — [string] name for the output file other than the default.
• output_prefix_override — [boolean] don't use prefix for output name.
• outputs — [file list] output files for actions and copy targets.
• partial_info_plist — [filename] path plist from asset catalog compiler.
• pool — [string] label of the pool used by binary targets and actions.
• post_processing_args — [string list] args for the post-processing script.

---

(and that's only part 1, bestie — part 2 is right there, don't move 💜)

• post_processing_manifest — [file] bestie, this is the name of the generated bundle manifest 🎀
• post_processing_outputs — [file list] the outputs of the post-processing step
• post_processing_script — [file name] the script for the post-processing step
• post_processing_sources — [file list] the sources for the post-processing step
• precompiled_header — [string] header file to precompile
• precompiled_header_type — [string] literally just "gcc" or "msvc", pick one 💅
• precompiled_source — [file name] source file to precompile
• product_type — [string] the product type for the bundle
• public — [file list] declare public header files for a target
• public_configs — [label list] configs applied to dependents
• public_deps — [label list] declare public dependencies
• public_inputs — [file list] declare public inputs
• rebase — [boolean] rebase collected metadata as files
• response_file_contents — [string list] contents of .rsp file for actions
• rustflags — [string list] flags passed to the Rust compiler 🦀
• script — [file name] script file for actions
• sources — [file list] source files for a target
• swiftflags — [string list] flags passed to the swift compiler
• target_xcode_platform — [string] the desired platform for the build
• testonly — [boolean] declares a target must only be used for testing
• transparent — [bool] true if the bundle is transparent
• validations — [label list] validation dependencies
• visibility — [label list] a list of labels that can depend on a target
• walk_keys — [string list] key(s) for managing the metadata collection walk
• weak_frameworks — [name list] name of frameworks that must be weak linked
• weak_libraries — [file list] file of libraries that must be weak linked
• write_runtime_deps — writes the target's runtime_deps to the given path
• xcasset_compiler_flags — [string list] flags passed to xcassets compiler
• xcode_extra_attributes — [scope] extra attributes for Xcode projects
• xcode_test_application_name — [string] name for Xcode test target

---

🫶 Other help topics 🫶

these are the other pages in the GN lore, bestie. run gn help <topic> and go off 💖

• all — print all the help at once (the whole buffet, no cap)
• buildargs — how build arguments work
• dotfile — info about the toplevel .gn file
• execution — build graph and execution overview
• grammar — language and grammar for GN build files
• input_conversion — processing input from exec_script and read_file
• file_pattern — matching more than one file
• label_pattern — matching more than one label
• labels — about labels
• metadata_collection — about metadata and its collection
• ninja_rules — how Ninja build rules are named
• nogncheck — annotating includes for checking
• output_conversion — specifies how to transform a value to output
• runtime_deps — how runtime dependency computation works
• source_expansion — map sources to outputs for scripts
• switches — show available command-line switches

---

and that's a wrap on the whole page, bestie 🎀✨ you just read gn 2598 (the build is f90c3d9df882, iconic, no notes 💅), dated October 2026. go build something gorgeous 🌈🦋 fr fr 💖