Glossary

Alias — the *name half of YAML's reuse mechanism: a reference to a block named by an anchor. Chapter 9.

Anchor — a name given to a block of YAML with &name, so other places can reuse it by alias or merge. Editing the anchor edits the shared value itself. Chapter 9.

Assignment (=) — an expression that outputs the whole document with a path set to a value. With -i, the file is rewritten. Contrast update-assignment. Chapter 4.

Document — one YAML value-stream inside a file; files can hold several, separated by ---. Chapter 7.

Document index — a document's position in its file, starting at 0, exposed to expressions as document_index. Chapter 7.

Expression — yq's name for its programs: the jq-like filter text between the command and the filenames. Takes a document in, produces documents (or values) out.

In place (-i) — the flag that makes an assignment expression rewrite its input file instead of printing to stdout. Powerful, unforgiving, and — with document-selecting expressions — capable of deleting unselected documents. Chapters 4 and 7.

Lexer error — the expression itself contains something yq's language doesn't have — a misspelling, or a jq operator that doesn't exist here. Reported with the position in the expression and the text it choked on. Chapters 3 and 11.

Merge key (<<) — the special key that folds an anchored map into another map at read time, with the local keys winning over the inherited ones. Chapter 9.

Node — one value in the parsed document tree: a map, a list, or a scalar, together with its tag and any comments attached to it.

Null — yq's answer for a path that doesn't exist: not an error, exit code 0, and a value that will travel silently into whatever reads it. Chapters 2 and 11.

Operator — one verb inside an expression: select, map, del, keys, and the rest.

Path — the dotted address of a value, .services.web.image; also, as an operator, the expression that reports a value's address as a list. Chapters 2 and 3.

Properties format — the flat key=value format of Java .properties files, with dots for nesting and no types. One of yq's -p/-o formats. Chapter 6.

Recursive descent (..) — "this node and everything beneath it." Chapter 3.

Round trip — converting a document away from YAML and back (typically through JSON). Faithful about data, fatal to comments and quoting style. Chapter 5.

Tag — a node's YAML type as written in the spec: !!str, !!int, !!bool, !!map. Also the operator that reports it — the inspection tool for YAML's type traps. Chapter 8.

Update-assignment (|=) — like assignment, but the new value is computed from the old one: .retries |= . + 1. Chapter 4.