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A playbook is one or more .ern files in the same directory. Errand reads all of them, merges their blocks, and runs the tasks you request.

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Block types

A playbook is made up of four block types:

errand

Playbook-level settings.

variable

A named input with an optional type and default.

computed

A value derived from an expression at runtime.

task

A named group of shell commands.
Every block except errand takes a name label. Names must be unique within each block type: 
variable "env" { ... }
computed "image_tag" { ... }
task "deploy" { ... }

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Evaluation order

Errand processes the playbook in three phases:
  1. Variables are resolved from defaults and --var flags.
  2. Computed blocks evaluate in dependency order, before any task runs.
  3. Tasks run in the order their dependencies require, with optional concurrency.

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References

Blocks refer to each other with dot notation. Referencing a block creates an implicit dependency: Errand ensures the referenced block runs first.
ReferenceRefers to
var.<name>A declared variable block
computed.<name>A declared computed block
task.<name>A declared task block
See references for the full dependency system, including cycle detection and explicit dependencies.