BUILD

load("//:tester.bzl", "greet")

greet(
    name = "a-greeting",
    my_name = "kristina",  
)

Console

$ bazel build :a-greeting
INFO: Found 1 target...
Target //:a-greeting up-to-date:
  bazel-bin/hi-there-kristina
INFO: Elapsed time: 0.324s, Critical Path: 0.00s

tester.bzl

def _impl(ctx):
  output = ctx.outputs.greeting
  ctx.file_action(
      output = output,
      content = "")

greet = rule(
    attrs = {"my_name": attr.string()},
    outputs = {"greeting": "hi-there-%{my_name}"},
    implementation = _impl,
)