🖥️jq

➡️This is a command-line reference manual for commands and command combinations that you don’t use often enough to remember it. This cheatsheet explains the jq command with important options and switches using examples.

4 minute read

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# A lightweight and flexible command-line JSON processor.

# Output a JSON file, in pretty-print format:
jq

# Output all elements from arrays
# (or all key-value pairs from objects) in a JSON file:
jq .[]

# Read JSON objects from a file into an array, and output it (inverse of jq .[]):
jq --slurp

# Output the first element in a JSON file:
jq .[0]

# Output the value of a given key of the first element in a JSON file:
jq .[0].key_name

# Output the value of a given key of each element in a JSON file:
jq 'map(.key_name)'
#
# [ { foo: 1 }, { foo: 2 } ] => [1, 2]

# Extract as stream of values instead of a list
jq '.[] | .foo'
#
# [ { "foo": 1 }, { "foo": 2 } ] => 1, 2

# Slicing
jq '.[1:2]'
#
# [ { "foo": 1 }, { "foo": 2 } ] => { "foo": 2 }

# Dictionary subset shorthand
jq 'map({ a, b })'
#
# [ { "a": 1, "b": 2, "c": 3 }, ...] => [ { "a": 1, "b": 2 }, ...]

# Parsing json
jq 'with_entries(.value |= fromjson)' --sort-keys
#
# { "b": "{}", "a": "{}" }
#   =>  { "a": {}, "b": {} }

# Serializing json
#
jq 'with_entries(.value |= tojson)' --sort-keys
#
# { "a": {}, "b": {} }
# => { "a": "{}", "b": "{}" }

# Flattening json
jq 'flatten(1)'
#
# [[1], [2]]
# => [1, 2]

# Converting to csv
jq '.[] | [.foo, .bar] | @csv' -r
# 
# [{ "foo": 1, "bar": 2, "baz":3 }]
# => 1,2

# Sort
jq 'sort'
# [3, 2, 1]
# => [1, 2, 3]

# Deleting duplicates (dedup / uniq)
jq unique
#
# [1, 1, 2, 1]
# => [1, 2]

# Sort lines of a file
jq --slurp '. | sort | .[]'

# Converting arbitrary data to json
jq -r '(map(keys) | add | unique | sort) as $cols | .[] as $row | $cols | map($row[.]) | @csv'
# [ { "foo": 1, "bar": 2}, { "foo": 3, "baz": 4}]
#
# => 2,,1
#    ,4,3
                                
										  
# Pretty print the json
jq "." < filename.json

# Access the value at key "foo"
jq '.foo'

# Access first list item
jq '.[0]'

# Slice & Dice
jq '.[2:4]'
jq '.[:3]'
jq '.[-2:]'

cat file.json | jq
# use jq to validate and pretty-print json output
# the `jq` tool can also be used do validate json files and pretty print output `cat file.json | jq` available on several platforms, including newer debian-based systems via `#sudo apt install jq`, mac via `brew install jq`, and from source https://stedolan.github.io/jq/download/ This is sample output - yours may be different.
success:
{
  "foo": "bar"
}

error:
$ echo '{"foo":{"bar":}}'| jq
parse error: Unmatched '}' at line 1, column 15

diff <(jq . -M -S < old.json) <(jq . -M -S < new.json)
# Get a diff of two json arrays - jq is amazing for manipulating json on the commandline, but the developers have some weird ideas about how to handle shell redirections. This command works around them. Further reading: https://github.com/stedolan/jq/issues/1110

jq < file.json
# Use jq to validate and pretty-print json output
# The `jq` tool can also be used do validate json files and pretty print output: ` jq < file.json` Available on several platforms, including newer debian-based systems via `#sudo apt install jq`, mac via `brew install jq`, and from source https://stedolan.github.io/jq/download/ This alternative to the original avoids the useless use of cat This is sample output - yours may be different.
success:
{
  "foo": "bar"
}

error:
$ jq < file.json
parse error: Unmatched '}' at line 1, column 15

#==============================##==============================#
# CMD JQ						       #
#==============================##==============================#

Cheatsheets are an excellent complement to other information sources like Linux man-pages, Linux help, or How-To’s and tutorials, as they provide compact and easily accessible information. While man-pages and detailed tutorials often contain comprehensive explanations and extensive guides, cheatsheets summarize the most important options forthe command jq in a clear format. This allows users to quickly access the needed information for jq without having to sift through lengthy texts. Especially in stressful situations or for recurring tasks, cheatsheets for jq are a valuable resource to work efficiently and purposefully.

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