Input JSON used for the examples:
# The 5 latest commits of the jqlang repository on GitHub
jqlang_commits=$(curl 'https://api.github.com/repos/jqlang/jq/commits?per_page=5')
Interactive Testing
Using a tool like ijq you can interactively work on JQ expressions.
Building New Objects
The output of one filter can be passed to another, which can commonly be used to build a new json object from an existing one.
echo $jqlang_commits | jq '.[0] | {message: .commit.message, name: .commit.committer.name}'
If you want to do this for a whole list of objects it works almost the same. The resulting objects are by default white space separated, which is best for processing in bash.
echo $jqlang_commits | jq '.[] | {message: .commit.message, name: .commit.committer.name}'
To expression can also be wrapped in [] , which will create a proper json list as the output.
echo $jqlang_commits | jq '[.[] | {message: .commit.message, name: .commit.committer.name}]'
Wrapping As List
Wrapping multiple json objects into a list is quite easy, just pass them to jq -s.
cat my-files/*.json | jq -s
Output Configuration
--raw-output / -r: If the output is a string, don’t wrap it in"". Useful for further processing in non json tools like shell loops.--sort-keys / -S: Output the fields of each object with the keys in sorted order.
Read Expression From File
Read the jq expression from a file instead of specifying in the command (Works similar to awk -f).
jq -f my-expression.jq
jq --from-file my-expression.jq
Array Slicing
jq can slice arrays, similar to how Python , using [n:m], where n is the inclusive start of the slice and m is the non-inclusive end of the slice.
So to grab the first 4 elements we can:
echo '["a","b","c","d","e","f"]' | jq -e '.[:4]'
Or the last 2
echo '["a","b","c","d","e","f"]' | jq -e '.[-2:]'
Turning stdout Into a List
Many command line tools provide one output item per line. If we want to process these further it can be useful to turn them into a JSON list.
find /var/www/html \
| grep "e.html" \
| jq -R -s 'split("\n")[:-1]'
This works by telling jq to accept raw input -R, slurp everything before processing -s, and then split it by newlines split("\n").
The final [:-1] is needed since the last element would otherwise be an empty string for the trailing newline of the output.