Paths & lenses

This page walks the engine's capabilities. Each is complete unless explicitly marked as a documented deferral.

Configuration tree

An ordered tree of labelled nodes with values, built by New(); every entry addressable by path, with Root, Label and node insertion/removal preserving order.

Path language

Absolute and relative paths, * name wildcard, // descendant axis, . / .., positional [n] / [last()], value [sub = 'v'], regexp [sub =~ 're'] (RE2), existence predicates, union |, and $var bindings.

Editing API

Get / Exists / Set / SetMultiple / Insert / Remove / Move / Match / Label / DefineVariable / DefineNode — the full tree-mutation surface over path expressions.

The embedded .aug corpus interpreter

A from-scratch, pure-Go interpreter for the Augeas lens DSL (internal/interp) reads the entire embedded upstream Augeas 1.14.1 lens corpus — all 232 modules, verbatim .aug sources under lenses/dist/ — plus five original contrib lenses (Wireguard, Rclone, Caddyfile, Nftables, Unbound) under lenses/contrib/. NewEngine().Lens(module, binding) (e.g. Lens("Hosts", "lns")) returns a Lens usable with TextStore / Get / Set / Match; Load / Save run through an injectable FileSystem seam, and load failures surface under /augeas//error. The interpreter's own get and put are verified correct against the corpus's inline test assertions (1791/1791, 100%), but the public Lens.Build for these interpreted lenses is not yet wired up — see "Deferred" in the README for what that means for TextRetrieve/Save today.

Writing your own lens

Register/LensByName are a pluggable seam: implement Lens (Parse/Build) in hand-written Go and register it under a name for full get+put round-trip control outside the interpreted corpus. No lens ships pre-registered.