Folha de dicas do Jq
Folha de dicas do comando JQ
jq is a command-line JSON processor: it slices, filters, maps and transforms structured data the way sed and awk do for text. A jq program is a filter — it takes an input, and produces an output.
# pretty-print a file
jq . data.json
# read from a pipe
curl -s https://api.example.com/users | jq '.[] | .name'
📦 Installation
brew install jq # macOS
apt install jq # Debian, Ubuntu
dnf install jq # Fedora, RHEL
choco install jq # Windows
🚩 Command-Line Flags
| Flag | Description |
|---|---|
-r, --raw-output | Print strings without quotes — what you want for shell variables |
-c, --compact-output | One compact line per result instead of pretty-printed JSON |
-n, --null-input | Do not read input; build JSON from scratch |
-s, --slurp | Read the whole input into one array |
-e, --exit-status | Exit non-zero when the last output is false or null |
-j, --join-output | Raw output with no newline between results |
--tab / --indent n | Indent with tabs, or with n spaces |
-S, --sort-keys | Sort object keys in the output |
--arg name value | Pass a string into the program as $name |
--argjson name json | Pass parsed JSON in as $name |
--slurpfile name f | Read a whole file into $name as an array |
--raw-input, -R | Treat each input line as a string instead of JSON |
🧭 Core Syntax
| Filter | Description |
|---|---|
. | The identity filter — the input, unchanged |
.foo | The value of field foo |
.foo.bar | Nested field access |
.foo? | Same, but stays quiet when the input is not an object |
."odd key" | A field whose name needs quoting |
.[] | Every element of an array (or every value of an object) |
.[0] | One element by index (-1 is the last) |
.[2:4] | A slice — see the table below |
| | Pipe: feed the result of the left filter into the right one |
, | Run both filters on the same input, emit both results |
() | Grouping |
// | Alternative: use the right side if the left is false/null |
? | Suppress errors from the preceding filter |
📇 Objects
| Task | Filter |
|---|---|
| List the keys | jq 'keys' (keys_unsorted to keep order) |
| Does a key exist? | jq 'has("foo")' |
| Pick a few fields | jq '{name, id}' |
| Rename while picking | jq '{title: .name, ref: .id}' |
| Delete a key | jq 'del(.foo)' |
| Add 1 to every value | jq 'map_values(.+1)' |
| Merge two objects | jq '.a * .b' (deep) or jq '.a + .b' (shallow) |
| Object → array of pairs | jq 'to_entries' |
| Array of pairs → object | jq 'from_entries' |
| Transform every entry | jq 'with_entries(.value += 1)' |
| Build an object from values | jq -n '{time: now, host: $ENV.HOSTNAME}' |
📚 Arrays
Slicing and filtering
| Task | Filter |
|---|---|
| Every element | jq '.[]' |
| First / last | jq '.[0]' / jq '.[-1]' |
| Range, first three, last two | jq '.[2:4]', jq '.[:3]', jq '.[-2:]' |
| Numbers above a threshold | jq 'map(select(. >= 2))' |
| Objects matching a field | jq '.[] | select(.id == "second")' |
| Several conditions | jq '.[] | select(.age > 18 and .city == "Oslo")' |
| By type | jq '.[] | numbers' — also strings, booleans, nulls, arrays, objects, iterables, scalars, values |
| Test a string field | jq '.[] | select(.name | test("^a"; "i"))' |
Mapping and transforming
| Task | Filter |
|---|---|
| Apply to every element | jq 'map(.+1)' |
| Pull one field out of each | jq 'map(.name)' or jq '.[].name' |
| Drop elements by index | jq 'del(.[1, 2])' |
| Concatenate nested arrays | jq 'add' |
| Flatten | jq 'flatten' (flatten(1) for one level) |
| Sort | jq 'sort' / jq 'sort_by(.foo)' |
| Group | jq 'group_by(.foo)' |
| Deduplicate | jq 'unique' / jq 'unique_by(.foo)' |
| Reverse | jq 'reverse' |
| Smallest / largest | jq 'min', jq 'max_by(.price)' |
| Count | jq 'length' |
| Sum | jq 'map(.amount) | add' |
| Any / all match | jq 'any(.active)', jq 'all(.age > 18)' |
| A range of numbers | jq '[range(2;4)]' |
| The type of each item | jq 'map(type)' |
🔤 Strings & Formatting
| Task | Filter |
|---|---|
| Interpolate | jq -r '"\(.name) is \(.age)"' |
| Change case | jq 'ascii_downcase' / ascii_upcase |
| Split and join | jq 'split(",")' / jq 'join(", ")' |
| Trim a prefix or suffix | jq 'ltrimstr("v")' / rtrimstr(".json") |
| Match a regex | jq 'test("^http")' |
| Replace | jq 'sub("^v"; "")' / gsub("\\s+"; "-") |
| Capture named groups | jq 'capture("(?<host>[^:]+):(?<port>\\d+)")' |
| CSV / TSV output | jq -r '.[] | [.id, .name] | @csv' |
| Escape for a URL or shell | jq -r '@uri "?q=\(.term)"', @sh |
| Base64 | jq -r '@base64' / jq -r '@base64d' |
| Object → JSON string | jq 'tojson' (and fromjson back) |
🔀 Conditionals & Errors
# if / then / else — 'end' is required
jq 'if .age >= 18 then "adult" else "minor" end'
# several branches
jq 'if .n > 100 then "big" elif .n > 10 then "medium" else "small" end'
# fall back when a value is missing or null
jq '.nickname // .name'
# keep going when a filter would fail
jq '.items[]? // empty'
# turn a failure into a value of your own
jq 'try (.a.b.c) catch "not found"'
# stop with a message
jq 'if .id == null then error("id is required") else . end'
🧮 Variables, Functions & Reduction
# bind a value to a variable
jq '.items[] as $item | $item.name'
# pass values in from the shell
jq --arg env prod '.deploys[] | select(.env == $env)'
jq --argjson min 10 '.[] | select(.count > $min)'
# define a reusable function
jq 'def is_active: .status == "active"; map(select(is_active))'
# accumulate a value
jq 'reduce .[] as $x (0; . + $x.amount)'
# keep the intermediate results too
jq '[foreach .[] as $x (0; . + $x; .)]'
# read the environment
jq -n 'env.HOME'
🛠 Everyday Recipes
# pretty-print, sorted, and back to a file
jq -S . data.json > sorted.json
# one field, unquoted, for use in a shell variable
version=$(jq -r .version package.json)
# every key of every object, deduplicated
jq -r '[.[] | keys[]] | unique[]' data.json
# turn an array of objects into a CSV with a header row
jq -r '(.[0] | keys_unsorted), (.[] | [.[]]) | @csv' data.json
# merge two JSON files
jq -s '.[0] * .[1]' a.json b.json
# read newline-delimited JSON (one object per line)
jq -c '.event' events.ndjson
# turn plain text lines into a JSON array
printf 'a\nb\n' | jq -R -s 'split("\n") | map(select(length > 0))'
# find the path to every occurrence of a key
jq -c 'paths(scalars) as $p | {path: $p, value: getpath($p)}' data.json
# rewrite every string in a document
jq 'walk(if type == "string" then ascii_downcase else . end)' data.json
# use the exit status in a script
jq -e '.errors | length == 0' report.json && echo "clean"