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Shell rules for Bazel
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Latest commit 39e3568 Jan 23, 2020

README.md

Shell rules for Bazel

This project extends Bazel with a toolchain for common shell commands.

Setup

See the WORKSPACE setup section of the current release.

Or use the following template in your WORKSPACE file to install a development version of rules_sh:

load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
http_archive(
    name = "rules_sh",
    # Replace git revision and sha256.
    sha256 = "0000000000000000000000000000000000000000000000000000000000000000",
    strip_prefix = "rules_sh-0000000000000000000000000000000000000000",
    urls = ["https://github.com/tweag/rules_sh/archive/0000000000000000000000000000000000000000.tar.gz"],
)
load("@rules_sh//sh:repositories.bzl", "rules_sh_dependencies")
rules_sh_dependencies()

Usage

Configure the toolchain

Add the following to your WORKSPACE file to configure a local POSIX toolchain.

load("@rules_sh//sh:posix.bzl", "sh_posix_configure")
sh_posix_configure()

Bazel will query PATH for common Unix shell commands. You can override the path to individual commands with environment variables of the form POSIX_<COMMAND_NAME>. E.g. POSIX_MAKE=/usr/bin/gmake.

Note, this introduces an inhermeticity to the build as the contents of PATH may be specific to your machine's setup.

Refer to rules_nixpkgs's nixpkgs_posix_configure for a hermetic alternative.

Use Unix tools in genrules

The POSIX toolchain exposes custom make variables of the form POSIX_<COMMAND_NAME> for discovered commands. Use these as follows:

genrule(
    name = "example",
    srcs = [":some-input-file"],
    outs = ["some-output-file"],
    cmd = "$(POSIX_GREP) some-pattern $(execpath :some-input-file.bzl) > $(OUTS)",
    toolchains = ["@rules_sh//sh/posix:make_variables"],
)

See posix.commands defined in @rules_sh//sh/posix.bzl for the list of known POSIX commands.

Use Unix tools in custom rules

The POSIX toolchain provides two attributes:

  • commands: A dict mapping names of commands to their paths.
  • paths: A deduplicated list of bindir paths suitable for generating $PATH.
def _my_rule_impl(ctx):
    posix_info = ctx.toolchains["@rules_sh//sh/posix:toolchain_type"]
    ctx.actions.run(
        executable = posix_info.commands["grep"],
        ...
    )
    ctx.actions.run_shell(
        command = "grep ...",
        env = {"PATH": ":".join(posix_info.paths)},
        ...
    )

my_rule = rule(
    _my_rule_impl,
    toolchains = ["@rules_sh//sh/posix:toolchain_type"],
    ...
)
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