jq · lesson 26 of 32 · Variables & functions

Variables

expr as $name | … binds a value for the rest of the pipeline — handy when you need it twice. A pattern on the left destructures objects and arrays.

Example 1Average age with a saved count

Document

{
  "team": "Platform",
  "office": { "city": "Berlin", "floor": 3 },
  "members": [
    { "name": "Ada", "age": 36, "role": "lead", "active": true,
      "email": "[email protected]", "skills": ["rust", "sql"] },
    { "name": "Linus", "age": 28, "role": "dev", "active": true,
      "email": null, "skills": ["c", "shell"] },
    { "name": "Grace", "age": 45, "role": "dev", "active": false,
      "skills": ["cobol"] },
    { "name": "Alan", "age": 41, "role": "qa", "active": true,
      "email": "[email protected]", "skills": [] }
  ]
}

Query

.members | length as $n | map(.age) | add / $n

length as $n Compute the length (4) and bind it to $n; the input stays the members array.
map(.age) | add The sum of the ages — . is still the members array here.
/ $n Divide by the saved count.

Result

37.5

Try it in the playground

Example 2Destructuring

Document

{
  "team": "Platform",
  "office": { "city": "Berlin", "floor": 3 },
  "members": [
    { "name": "Ada", "age": 36, "role": "lead", "active": true,
      "email": "[email protected]", "skills": ["rust", "sql"] },
    { "name": "Linus", "age": 28, "role": "dev", "active": true,
      "email": null, "skills": ["c", "shell"] },
    { "name": "Grace", "age": 45, "role": "dev", "active": false,
      "skills": ["cobol"] },
    { "name": "Alan", "age": 41, "role": "qa", "active": true,
      "email": "[email protected]", "skills": [] }
  ]
}

Query

. as {team: $t, office: {city: $c}} | "\($t) in \($c)"

{team: $t, office: {city: $c}} A pattern: pull team into $t and office.city into $c in one go.
"\($t) in \($c)" Use the variables like any value — here, inside a string.

Result

"Platform in Berlin"

Try it in the playground

Good to know

A variable is visible only to the right of its as, up to the end of the enclosing pipeline or parentheses.