README.md

Examples demonstrating "Make" variables

These examples demonstrate Bazel's "Make" variable support.

Predefined variables

//testapp:show_predefined_variables demonstrates predefined variables available to all rules. These are parsed in any attribute marked "Subject to 'Make Variable' substitution".

$ bazel build //testapp:show_predefined_variables && cat bazel-bin/testapp/show_predefined_variables.out
COMPILATION_MODE: fastbuild
BINDIR: bazel-out/x86-fastbuild/bin
GENDIR: bazel-out/x86-fastbuild/bin
TARGET_CPU: x86

Predefined genrule variables

All genrules

//testapp:show_genrule_variables demonstrates predefined variables exclusively available to genrule.

$ bazel build //testapp:show_genrule_variables && cat bazel-bin/testapp/subdir/show_genrule_variables1.out
SRCS: testapp/show_genrule_variables1.src testapp/show_genrule_variables2.src
OUTS: bazel-out/x86-fastbuild/bin/testapp/subdir/show_genrule_variables1.out bazel-out/x86-fastbuild/bin/testapp/subdir/show_genrule_variables2.out
RULEDIR: bazel-out/x86-fastbuild/bin/testapp
@D (prefer RULEDIR to this): bazel-out/x86-fastbuild/bin/testapp
 * Because this genrule has multiple outputs, @D is the same as RULEDIR.

Genrules with one input or output

//testapp:single_file_genrule demonstrates predefined variables exclusively available to genrules that consume a single source file or produce a single output file.

$ bazel build //testapp:single_file_genrule && cat bazel-bin/testapp/subdir/single_file_genrule.out
<: testapp/show_genrule_variables1.src
@: bazel-out/x86-fastbuild/bin/testapp/subdir/single_file_genrule.out
RULEDIR: bazel-out/x86-fastbuild/bin/testapp
@D: bazel-out/x86-fastbuild/bin/testapp/subdir
 * Because this genrule has one input, < is a valid variable.
 * Because this genrule has one output, @ is a valid variable.
 * Because this genrule has one output, @D is different than RULEDIR.

Predefined path variables

//testapp:show_app_output demonstrates predefined variables related to source and output paths.

$ bazel build //testapp:show_app_output && cat bazel-bin/testapp/app_output
:app output paths
 execpath: bazel-out/host/bin/testapp/app
 runfiles: testapp/app
 location: bazel-out/host/bin/testapp/app

source file paths
 execpath: testapp/empty.source
 runfiles: testapp/empty.source
 location: testapp/empty.source

Custom Starlark-defined variables

//testapp:show_custom_var demonstrates custom variable defined in Starlrak.

$ bazel build //testapp:show_custom_var && cat bazel-bin/testapp/custom_var
Target //testapp:show_custom_var up-to-date:
  bazel-bin/testapp/custom_var
INFO: Build completed successfully, 2 total actions
FOO is equal to bar!