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jq-A command-line JSON processor

https://cameronnokes.com/blog/working-with-json-in-bash-using-jq/April 20, 2021

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Remove unused dependencies from package.json
Get a property
Iteration
Extract the first item from output

jq is a lightweight and flexible command-line JSON processor. jq is like sed for JSON data. You can use it to slice and filter and map and transform structured data with the same ease that sed and grep let you play with text.

jq Cheat Sheet

Remove unused dependencies from package.json

set -e

# function to grep for a dependency
grep_dep() {
  # params: $1 = the string to grep for, $2 = directory to grep in

  # [1]
  grep --include="*.js" --exclude-dir="node_modules" -R --color -n "require\(.*$1.*\)" "$2"

  # if grep returns 0 results, it has an exit code of 1. No results means dependency is not in use
  if [[ $? > 0 ]]; then
    echo
    echo "** No uses of $1 found, consider removing. **"
    echo
  fi
}

# [2]
export -f grep_dep

# [3]
jq -r '.dependencies | keys | .[]' package.json | \
  # [4]
  xargs -I '{}' -P 4 -t bash -c "grep_dep '{}' ."

Get a property

echo '{ "foo": 123, "bar": 456 }' | jq '.foo'
# 123

Be sure to always wrap your jq selector in a single-quotes, otherwise bash tries to interpret all the symbols like ., whereas we want jq to do that.

Iteration

echo '[ {"id": 1}, {"id": 2} ]' | jq '.[].id'
# 1,2

Returns the number of dependencies and devDependencies a package.json contains.

jq -r '[(.dependencies, .devDependencies) | keys] | flatten | length' package.json

Extract the first item from output

curl 'https://api.github.com/repos/stedolan/jq/commits?per_page=5' | jq '.[0]'

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