SKILL.md

name: jq description: Use when the user needs to query, filter, reshape, extract, create, or construct JSON data — including API responses, config files, log output, or any structured data — or when helping the user write or debug JSON transformations.

jq — Built-in JSON Processor

Crush ships a built-in jq command (via github.com/itchyny/gojq) available in the bash tool. No external binary is required.

Supported Flags

Flag Description
-r, --raw-output Output strings without quotes
-j, --join-output Like -r but no trailing newline
-c, --compact-output One-line JSON output
-s, --slurp Read all inputs into an array
-n, --null-input Use null as input (ignore stdin)
-e, --exit-status Exit 1 if last output is false or null
-R, --raw-input Read each line as a string, not JSON
--arg name value Bind $name to a string value
--argjson name value Bind $name to a parsed JSON value

File arguments after the filter are also supported: jq '.foo' file.json.

Differences from Standard jq

The built-in uses gojq, which is a pure-Go jq implementation. Key differences:

  • No object key ordering — keys are sorted by default; keys_unsorted and -S are unavailable.
  • Arbitrary-precision integers — large integers keep full precision (addition, subtraction, multiplication, modulo, division when divisible).
  • String indexing — "abcde"[2] returns "c".
  • Not supported — --ascii-output, --seq, --stream, --stream-errors, -f/--from-file, --slurpfile, --rawfile, --args, --jsonargs, input_line_number, $__loc__, some regex features (backreferences, look-around).
  • YAML — gojq supports --yaml-input/--yaml-output but the built-in does not currently expose these flags.

Common Patterns

Extract a field:

echo '{"name":"crush"}' | jq '.name'

Filter an array:

echo '[1,2,3,4,5]' | jq '[.[] | select(. > 3)]'

Reshape objects:

echo '{"first":"Ada","last":"Lovelace"}' | jq '{full: (.first + " " + .last)}'

Use variables:

echo '{}' | jq --arg host localhost --argjson port 8080 '{host: $host, port: $port}'

Slurp multiple JSON values:

echo '{"a":1}{"b":2}' | jq -s '.'

Compact output for piping:

echo '{"a":1}' | jq -c '.a += 1'

Raw string output:

echo '["one","two","three"]' | jq -r '.[]'

Process a file:

jq '.dependencies | keys' package.json

Null input for constructing JSON:

jq -n --arg msg hello '{"message": $msg}'

Tips

  • Pipe jq output to other commands: jq -r '.url' data.json | xargs curl
  • Chain filters with | inside the expression, not shell pipes.
  • Use try to suppress errors on missing keys: jq 'try .foo.bar'
  • Use // "default" for fallback values: jq '.name // "unknown"'
  • Use @csv, @tsv, @base64, @html, @uri for format strings.