3. Facts, variables, and ordering

Gather host facts into variables, target steps with conditions, and sequence them with requires.

Before you start: Your first convergence

A gather block runs a gatherer before any step and binds its result to a name — gather "os" { from = "core.os_info" } makes os.family available to every expression. vars declares your own values (evaluated lazily, so they can reference gathered facts); --var KEY=VALUE overrides either from the CLI.

Steps run in dependency order, not file order: requires draws the edges of a DAG and independent steps may run in parallel. requires is ordering only — it is not a success demand. condition gates a step on an expression; a false condition skips it rather than failing it.

§ 1Exercise: Gate a step on a gathered fact

In the scaffolded playbook, add a variable derived from the os gatherer and a second step that only runs on Linux and requires the first.

gather "os" { from = "core.os_info" }

vars {
  is_linux = os.family == "linux"
}

play "baseline" {
  step "make-a" {
    resource   = "core.file_present"
    properties { path = "/var/tmp/weave-a.txt"  content = "alpha" }
  }
  step "make-b" {
    resource   = "core.file_present"
    condition  = is_linux
    requires   = ["make-a"]
    properties { path = "/var/tmp/weave-b.txt"  content = "beta" }
  }
}