Command line

Installing the wheel installs a small yaml command next to the library. It edits a single YAML file by path from the shell — handy in scripts, CI, or when a one-line change does not justify opening an editor:

yaml <file> <get|set|del> <path> [value]

$ yaml config.yaml get service.port
8080
$ yaml config.yaml set service.port 9090
$ yaml config.yaml get service.port
9090

The same engine powers the command, so everything the command does not touch keeps its original comments, indentation, and scalar styles.

1. Paths

Paths are dot-separated. Each segment descends one mapping key; a segment that is all digits addresses an item of the sequence at that point:

yaml config.yaml get service.port          # mapping key
yaml config.yaml get servers.0.host        # first item of the `servers` sequence

A mapping key that only contains digits stays a string key: foo.0 reads the "0" key inside foo, never a sequence index. Keys containing dots cannot be addressed. Every segment must be non-empty (a..b is rejected).

2. `get`

get prints the value at the path as YAML. Scalars print on one line (8080, true, hello world); collections print as a YAML block:

$ yaml config.yaml get servers.0
host: h1
port: 8080

A missing path exits with code 1 and names the deepest segment that could be resolved.

3. `set` creates missing chains

set writes the value at the path, creating intermediate mappings that do not exist yet — the whole chain, not just the leaf:

$ yaml config.yaml set tls.enabled true
$ yaml config.yaml get tls
enabled: true

This also works on an empty file, so yaml new.yaml set a.b 1 produces a valid two-line document.

The value argument is interpreted as YAML, which makes typing explicit:

Argument	Stored as
`123`	integer `123`
`true` / `false`	booleans
`1.5`	float
`null`	null
`[1, 2, 3]`	a list
`hello world`	the string `"hello world"`
`"'123'"`	the string `"123"` (shell-stripped quotes force a string)

Wrap a value in quotes to keep text like 123 or true textual. Setting into a sequence replaces an existing item (servers.0.port 8080); it does not append or grow the sequence.

4. `del`

del removes the node at the path — a leaf, a whole block-valued entry, or a sequence item:

$ yaml config.yaml del service.debug

Deleting the last child of an entry leaves key: {} (or key: [] for a sequence) so the file keeps reading back as an empty collection rather than null. A missing path exits with code 1 and changes nothing.

5. What stays byte-identical

The command loads the file with the same round-trip engine as the library and patches only the spans it changes:

comments, blank lines, and formatting elsewhere are preserved exactly;
a set of an existing scalar rewrites just that scalar;
a newly created chain is appended in canonical form (two-space indents by default) — it has no source layout to preserve.

Only single-document files are accepted; a multi-document file exits with an error instead of silently dropping the other documents.

6. Exit codes

Code	Meaning
`0`	success (`get` prints the value)
`1`	runtime failure: missing file, missing path, parse error, multi-document input
`2`	usage error: unknown command, malformed path, wrong argument count

yaml --help prints the usage summary.