BUILD

load("//:fun-with-outputs.bzl", "my_rule")

my_rule(
    name = "foo",
    many_results = [
        "212",
        "917",
        "646",
    ],
    one_result = "brooklyn",
)

Command line output

$ bazel build :foo
INFO: Found 1 target...
>>>>> # //:foo [action 'Generating 212']
(cd home/kchodorow/.cache/bazel/_bazel_kchodorow/f454bcbe3fb58b7971b0951d116298e9/execroot/class-workspace && \
  exec env - \
  /bin/bash -c 'touch bazel-out/local-fastbuild/bin/212 bazel-out/local-fastbuild/bin/917 bazel-out/local-fastbuild/bin/646')
Target //:foo up-to-date:
  bazel-bin/brooklyn
  bazel-bin/212
  bazel-bin/917
  bazel-bin/646
INFO: Elapsed time: 1.744s, Critical Path: 0.09s

fun-with-outputs.bzl

def _impl(ctx):
  ctx.file_action(
      output = ctx.outputs.one_result,
      content = "I'm bespoke.",
  )
  ctx.action(
      outputs = ctx.outputs.many_results,
      command = "touch %s" % " ".join([p.path for p in ctx.outputs.many_results]),
  )

my_rule = rule(
    implementation = _impl,
    attrs = {
        'one_result' : attr.output(),
        'many_results' : attr.output_list(),
    }
)