Skylark rule with output

BUILD

load("//:output.bzl", "my_rule")

my_rule(name = "foo")

Output

INFO: Found 1 target...
>>>>> # //:foo [action 'Generating b']
(cd /home/kchodorow/.cache/bazel/_bazel_kchodorow/f454bcbe3fb58b7971b0951d116298e9/execroot/class-workspace && \
  exec env - \
  /bin/bash -c 'touch a; touch bazel-out/local-fastbuild/bin/b')
Target //:foo up-to-date:
  bazel-bin/b
INFO: Elapsed time: 9.406s, Critical Path: 9.16s

output.bzl

def _rule_impl(ctx):
  ctx.action(
    outputs = [ctx.outputs.b], 
    command = "touch a; touch %s" % ctx.outputs.b.path)

my_rule = rule(
    implementation = _rule_impl,  
    outputs = {'b' : 'b'}
)