jq Cheat Sheet: Filters, Selectors & Transformations

The jq filters and selectors for slicing JSON in one quick reference.

Select, filter, and reshape JSON on the command line with jq.

Selectors

Filter	Does
.key	Field value
.a.b.c	Nested field
.[]	Iterate array/object values
.[0]	First element
.key // "x"	Default if null
.["weird-key"]	Bracket access

Transform

Filter	Does
map(.name)	Project a field
select(.age > 18)	Keep matching
{name, id}	Reshape object
group_by(.type)	Group
sort_by(.ts)	Sort
length	Count / string length
keys	Object keys

Flags & examples

Terminal

jq -r '.items[].name' data.json     # -r: raw strings
jq '.[] | select(.active)' data.json
jq -n --arg v "$VAL" '{value: $v}'  # build from shell var
curl -s api/x | jq '.data | length'

Key takeaways

-r outputs raw strings (no quotes) for shell consumption.
select() filters; map() projects across an array.
--arg safely injects a shell variable into a jq program.

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