NAME¶
jq - Command-line JSON processor
SYNOPSIS¶
jq [
options...]
filter [
files...]
jq can transform JSON in various ways, by selecting, iterating, reducing
and otherwise mangling JSON documents. For instance, running the command
jq
´map(.price) | add´ will take an array of JSON objects as input
and return the sum of their "price" fields.
By default,
jq reads a stream of JSON objects (whitespace separated) from
stdin. One or more
files may be specified, in which case
jq will read input from those instead.
The
options are described in the
INVOKING JQ section, they mostly
concern input and output formatting. The
filter is written in the jq
language and specifies how to transform the input document.
FILTERS¶
A jq program is a "filter": it takes an input, and produces an output.
There are a lot of builtin filters for extracting a particular field of an
object, or converting a number to a string, or various other standard tasks.
Filters can be combined in various ways - you can pipe the output of one filter
into another filter, or collect the output of a filter into an array.
Some filters produce multiple results, for instance there´s one that
produces all the elements of its input array. Piping that filter into a second
runs the second filter for each element of the array. Generally, things that
would be done with loops and iteration in other languages are just done by
gluing filters together in jq.
It´s important to remember that every filter has an input and an output.
Even literals like "hello" or 42 are filters - they take an input
but always produce the same literal as output. Operations that combine two
filters, like addition, generally feed the same input to both and combine the
results. So, you can implement an averaging filter as
add / length -
feeding the input array both to the
add filter and the
length
filter and dividing the results.
But that´s getting ahead of ourselves. :) Let´s start with something
simpler:
INVOKING JQ¶
jq filters run on a stream of JSON data. The input to jq is parsed as a sequence
of whitespace-separated JSON values which are passed through the provided
filter one at a time. The output(s) of the filter are written to standard out,
again as a sequence of whitespace-separated JSON data.
Note: it is important to mind the shell´s quoting rules. As a general rule
it´s best to always quote (with single-quote characters) the jq program,
as too many characters with special meaning to jq are also shell
meta-characters. For example,
jq "foo" will fail on most Unix
shells because that will be the same as
jq foo, which will generally
fail because
foo is not defined. When using the Windows command shell
(cmd.exe) it´s best to use double quotes around your jq program when
given on the command-line (instead of the
-f program-file option), but
then double-quotes in the jq program need backslash escaping.
You can affect how jq reads and writes its input and output using some
command-line options:
- •
- --version:
- Output the jq version and exit with zero.
- •
- --slurp/-s:
- Instead of running the filter for each JSON object in the
input, read the entire input stream into a large array and run the filter
just once.
- •
- --online-input/-I:
- When the top-level input value is an array produce its
elements instead of the array. This allows on-line processing of
potentially very large top-level arrays´ elements.
- •
- --raw-input/-R:
- Don´t parse the input as JSON. Instead, each line of
text is passed to the filter as a string. If combined with --slurp,
then the entire input is passed to the filter as a single long
string.
- •
- --null-input/-n:
- Don´t read any input at all! Instead, the filter is
run once using null as the input. This is useful when using jq as a
simple calculator or to construct JSON data from scratch.
- •
- --compact-output / -c:
- By default, jq pretty-prints JSON output. Using this option
will result in more compact output by instead putting each JSON object on
a single line.
- •
- --colour-output / -C and
--monochrome-output / -M:
- By default, jq outputs colored JSON if writing to a
terminal. You can force it to produce color even if writing to a pipe or a
file using -C, and disable color with -M.
- •
- --ascii-output / -a:
- jq usually outputs non-ASCII Unicode codepoints as UTF-8,
even if the input specified them as escape sequences (like
"\u03bc"). Using this option, you can force jq to produce pure
ASCII output with every non-ASCII character replaced with the equivalent
escape sequence.
- •
- --unbuffered
- Flush the output after each JSON object is printed (useful
if you´re piping a slow data source into jq and piping jq´s
output elsewhere).
- •
- --sort-keys / -S:
- Output the fields of each object with the keys in sorted
order.
- •
- --raw-output / -r:
- With this option, if the filter´s result is a string
then it will be written directly to standard output rather than being
formatted as a JSON string with quotes. This can be useful for making jq
filters talk to non-JSON-based systems.
- •
- -f filename / --from-file filename:
- Read filter from the file rather than from a command line,
like awk´s -f option. You can also use ´#´ to make
comments.
- •
- -e / --exit-status:
- Sets the exit status of jq to 0 if the last output values
was neither false nor null, 1 if the last output value was
either false or null, or 4 if no valid result was ever
produced. Normally jq exits with 2 if there was any usage problem or
system error, 3 if there was a jq program compile error, or 0 if the jq
program ran.
- •
- --arg name value:
- This option passes a value to the jq program as a
predefined variable. If you run jq with --arg foo bar, then
$foo is available in the program and has the value
"bar".
- •
- --argfile name filename:
- This option passes the first value from the named file as a
value to the jq program as a predefined variable. If you run jq with
--argfile foo bar, then $foo is available in the program and
has the value resulting from parsing the content of the file named
bar.
-
BASIC FILTERS¶
The absolute simplest (and least interesting) filter is
.. This is a
filter that takes its input and produces it unchanged as output.
Since jq by default pretty-prints all output, this trivial program can be a
useful way of formatting JSON output from, say,
curl.
-
-
jq ´.´
"Hello, world!"
=> "Hello, world!"
-
.foo, .foo.bar¶
The simplest
useful filter is
.foo. When given a JSON object (aka
dictionary or hash) as input, it produces the value at the key
"foo", or null if there´s none present.
If the key contains special characters, you need to surround it with double
quotes like this:
."foo$".
A filter of the form
.foo.bar is equivalent to
.foo|.bar.
-
-
jq ´.foo´
{"foo": 42, "bar": "less interesting data"}
=> 42
jq ´.foo´
{"notfoo": true, "alsonotfoo": false}
=> null
jq ´.["foo"]´
{"foo": 42}
=> 42
-
.foo?¶
Just like
.foo, but does not output even an error when
. is not an
array or an object.
-
-
jq ´.foo?´
{"foo": 42, "bar": "less interesting data"}
=> 42
jq ´.foo?´
{"notfoo": true, "alsonotfoo": false}
=> null
jq ´.["foo"]?´
{"foo": 42}
=> 42
jq ´[.foo?]´
[1,2]
=> []
-
.[<string>], .[2], .[10:15]¶
You can also look up fields of an object using syntax like
.["foo"] (.foo above is a shorthand version of this). This
one works for arrays as well, if the key is an integer. Arrays are zero-based
(like javascript), so
.[2] returns the third element of the array.
The
.[10:15] syntax can be used to return a subarray of an array or
substring of a string. The array returned by
.[10:15] will be of length
5, containing the elements from index 10 (inclusive) to index 15 (exclusive).
Either index may be negative (in which case it counts backwards from the end
of the array), or omitted (in which case it refers to the start or end of the
array).
The
? "operator" can also be used with the slice operator, as
in
.[10:15]?, which outputs values where the inputs are slice-able.
-
-
jq ´.[0]´
[{"name":"JSON", "good":true}, {"name":"XML", "good":false}]
=> {"name":"JSON", "good":true}
jq ´.[2]´
[{"name":"JSON", "good":true}, {"name":"XML", "good":false}]
=> null
jq ´.[2:4]´
["a","b","c","d","e"]
=> ["c", "d"]
jq ´.[2:4]´
"abcdefghi"
=> "cd"
jq ´.[:3]´
["a","b","c","d","e"]
=> ["a", "b", "c"]
jq ´.[-2:]´
["a","b","c","d","e"]
=> ["d", "e"]
-
.[]¶
If you use the
.[index] syntax, but omit the index entirely, it will
return
all of the elements of an array. Running
.[] with the
input
[1,2,3] will produce the numbers as three separate results,
rather than as a single array.
You can also use this on an object, and it will return all the values of the
object.
-
-
jq ´.[]´
[{"name":"JSON", "good":true}, {"name":"XML", "good":false}]
=> {"name":"JSON", "good":true}, {"name":"XML", "good":false}
jq ´.[]´
[]
=>
jq ´.[]´
{"a": 1, "b": 1}
=> 1, 1
-
.[]?¶
Like
.[], but no errors will be output if . is not an array or object.
If two filters are separated by a comma, then the input will be fed into both
and there will be multiple outputs: first, all of the outputs produced by the
left expression, and then all of the outputs produced by the right. For
instance, filter
.foo, .bar, produces both the "foo" fields
and "bar" fields as separate outputs.
-
-
jq ´.foo, .bar´
{"foo": 42, "bar": "something else", "baz": true}
=> 42, "something else"
jq ´.user, .projects[]´
{"user":"stedolan", "projects": ["jq", "wikiflow"]}
=> "stedolan", "jq", "wikiflow"
jq ´.[4,2]´
["a","b","c","d","e"]
=> "e", "c"
-
The | operator combines two filters by feeding the output(s) of the one on the
left into the input of the one on the right. It´s pretty much the same as
the Unix shell´s pipe, if you´re used to that.
If the one on the left produces multiple results, the one on the right will be
run for each of those results. So, the expression
.[] | .foo retrieves
the "foo" field of each element of the input array.
-
-
jq ´.[] | .name´
[{"name":"JSON", "good":true}, {"name":"XML", "good":false}]
=> "JSON", "XML"
-
TYPES AND VALUES¶
jq supports the same set of datatypes as JSON - numbers, strings, booleans,
arrays, objects (which in JSON-speak are hashes with only string keys), and
"null".
Booleans, null, strings and numbers are written the same way as in javascript.
Just like everything else in jq, these simple values take an input and produce
an output -
42 is a valid jq expression that takes an input, ignores
it, and returns 42 instead.
Array construction - []¶
As in JSON,
[] is used to construct arrays, as in
[1,2,3]. The
elements of the arrays can be any jq expression. All of the results produced
by all of the expressions are collected into one big array. You can use it to
construct an array out of a known quantity of values (as in
[.foo, .bar,
.baz]) or to "collect" all the results of a filter into an array
(as in
[.items[].name])
Once you understand the "," operator, you can look at jq´s array
syntax in a different light: the expression
[1,2,3] is not using a
built-in syntax for comma-separated arrays, but is instead applying the
[] operator (collect results) to the expression 1,2,3 (which produces
three different results).
If you have a filter
X that produces four results, then the expression
[X] will produce a single result, an array of four elements.
-
-
jq ´[.user, .projects[]]´
{"user":"stedolan", "projects": ["jq", "wikiflow"]}
=> ["stedolan", "jq", "wikiflow"]
-
Objects - {}¶
Like JSON,
{} is for constructing objects (aka dictionaries or hashes),
as in:
{"a": 42, "b": 17}.
If the keys are "sensible" (all alphabetic characters), then the
quotes can be left off. The value can be any expression (although you may need
to wrap it in parentheses if it´s a complicated one), which gets applied
to the {} expression´s input (remember, all filters have an input and an
output).
-
-
{foo: .bar}
-
will produce the JSON object
{"foo": 42} if given the JSON
object
{"bar":42, "baz":43}. You can use this to
select particular fields of an object: if the input is an object with
"user", "title", "id", and "content"
fields and you just want "user" and "title", you can write
-
-
{user: .user, title: .title}
-
Because that´s so common, there´s a shortcut syntax:
{user,
title}.
If one of the expressions produces multiple results, multiple dictionaries will
be produced. If the input´s
-
-
{"user":"stedolan","titles":["JQ Primer", "More JQ"]}
-
then the expression
-
-
{user, title: .titles[]}
-
will produce two outputs:
-
-
{"user":"stedolan", "title": "JQ Primer"}
{"user":"stedolan", "title": "More JQ"}
-
Putting parentheses around the key means it will be evaluated as an expression.
With the same input as above,
-
-
{(.user): .titles}
-
produces
-
-
{"stedolan": ["JQ Primer", "More JQ"]}
jq ´{user, title: .titles[]}´
{"user":"stedolan","titles":["JQ Primer", "More JQ"]}
=> {"user":"stedolan", "title": "JQ Primer"}, {"user":"stedolan", "title": "More JQ"}
jq ´{(.user): .titles}´
{"user":"stedolan","titles":["JQ Primer", "More JQ"]}
=> {"stedolan": ["JQ Primer", "More JQ"]}
-
BUILTIN OPERATORS AND FUNCTIONS¶
Some jq operator (for instance,
+) do different things depending on the
type of their arguments (arrays, numbers, etc.). However, jq never does
implicit type conversions. If you try to add a string to an object you´ll
get an error message and no result.
Addition - +¶
The operator
+ takes two filters, applies them both to the same input,
and adds the results together. What "adding" means depends on the
types involved:
- •
- Numbers are added by normal arithmetic.
- •
- Arrays are added by being concatenated into a larger
array.
- •
- Strings are added by being joined into a larger
string.
- •
- Objects are added by merging, that is, inserting all
the key-value pairs from both objects into a single combined object. If
both objects contain a value for the same key, the object on the right of
the + wins. (For recursive merge use the * operator.)
-
null can be added to any value, and returns the other value unchanged.
-
-
jq ´.a + 1´
{"a": 7}
=> 8
jq ´.a + .b´
{"a": [1,2], "b": [3,4]}
=> [1,2,3,4]
jq ´.a + null´
{"a": 1}
=> 1
jq ´.a + 1´
{}
=> 1
jq ´{a: 1} + {b: 2} + {c: 3} + {a: 42}´
null
=> {"a": 42, "b": 2, "c": 3}
-
Subtraction - -¶
As well as normal arithmetic subtraction on numbers, the
- operator can
be used on arrays to remove all occurences of the second array´s elements
from the first array.
-
-
jq ´4 - .a´
{"a":3}
=> 1
jq ´. - ["xml", "yaml"]´
["xml", "yaml", "json"]
=> ["json"]
-
Multiplication, division, modulo - *, /, and %¶
These operators only work on numbers, and do the expected.
Multiplying a string by a number produces the concatenation of that string that
many times.
Dividing a string by another splits the first using the second as separators.
Multiplying two objects will merge them recursively: this works like addition
but if both objects contain a value for the same key, and the values are
objects, the two are merged with the same strategy.
-
-
jq ´10 / . * 3´
5
=> 6
jq ´. / ", "´
"a, b,c,d, e"
=> ["a","b,c,d","e"]
jq ´{"k": {"a": 1, "b": 2}} * {"k": {"a": 0,"c": 3}}´
null
=> {"k": {"a": 0, "b": 2, "c": 3}}
-
length¶
The builtin function
length gets the length of various different types of
value:
- •
- The length of a string is the number of Unicode
codepoints it contains (which will be the same as its JSON-encoded length
in bytes if it´s pure ASCII).
- •
- The length of an array is the number of
elements.
- •
- The length of an object is the number of key-value
pairs.
- •
- The length of null is zero.
- jq ´.[] | length´
-
-
[[1,2], "string", {"a":2}, null]
-
- => 2, 6, 1, 0
-
keys¶
The builtin function
keys, when given an object, returns its keys in an
array.
The keys are sorted "alphabetically", by unicode codepoint order. This
is not an order that makes particular sense in any particular language, but
you can count on it being the same for any two objects with the same set of
keys, regardless of locale settings.
When
keys is given an array, it returns the valid indices for that array:
the integers from 0 to length-1.
-
-
jq ´keys´
{"abc": 1, "abcd": 2, "Foo": 3}
=> ["Foo", "abc", "abcd"]
jq ´keys´
[42,3,35]
=> [0,1,2]
-
has¶
The builtin function
has returns whether the input object has the given
key, or the input array has an element at the given index.
has($key) has the same effect as checking whether
$key is a member
of the array returned by
keys, although
has will be faster.
-
-
jq ´map(has("foo"))´
[{"foo": 42}, {}]
=> [true, false]
jq ´map(has(2))´
[[0,1], ["a","b","c"]]
=> [false, true]
-
del¶
The builtin function
del removes a key and its corresponding value from
an object.
-
-
jq ´del(.foo)´
[{"foo": 42, "bar": 9001, "baz": 42}]
=> {"bar": 9001, "baz": 42}
jq ´del(.[1, 2])´
[["foo", "bar", "baz"]]
=> ["foo"]
-
to_entries, from_entries, with_entries¶
These functions convert between an object and an array of key-value pairs. If
to_entries is passed an object, then for each
k: v entry in the
input, the output array includes
{"key": k, "value":
v}.
from_entries does the opposite conversion, and
with_entries(foo)
is a shorthand for
to_entries | map(foo) | from_entries, useful for
doing some operation to all keys and values of an object.
-
-
jq ´to_entries´
{"a": 1, "b": 2}
=> [{"key":"a", "value":1}, {"key":"b", "value":2}]
jq ´from_entries´
[{"key":"a", "value":1}, {"key":"b", "value":2}]
=> {"a": 1, "b": 2}
jq ´with_entries(.key |= "KEY_" + .)´
{"a": 1, "b": 2}
=> {"KEY_a": 1, "KEY_b": 2}
-
select¶
The function
select(foo) produces its input unchanged if
foo
returns true for that input, and produces no output otherwise.
It´s useful for filtering lists:
[1,2,3] | map(select(. >= 2))
will give you
[2,3].
-
-
jq ´map(select(. >= 2))´
[1,5,3,0,7]
=> [5,3,7]
-
arrays, objects, iterables, booleans, numbers, strings, nulls,
values, scalars¶
These built-ins select only inputs that are arrays, objects, iterables (arrays
or objects), booleans, numbers, strings, null, non-null values, and
non-iterables, respectively.
-
-
jq ´.[]|numbers´
[[],{},1,"foo",null,true,false]
=> 1
-
empty¶
empty returns no results. None at all. Not even
null.
It´s useful on occasion. You´ll know if you need it :)
-
-
jq ´1, empty, 2´
null
=> 1, 2
jq ´[1,2,empty,3]´
null
=> [1,2,3]
-
map(x)¶
For any filter
x,
map(x) will run that filter for each element of
the input array, and produce the outputs a new array.
map(.+1) will
increment each element of an array of numbers.
map(x) is equivalent to
[.[] | x]. In fact, this is how it´s
defined.
-
-
jq ´map(.+1)´
[1,2,3]
=> [2,3,4]
-
paths¶
Outputs the paths to all the elements in its input (except it does not output
the empty list, representing . itself).
paths is equivalent to
-
-
def paths: path(recurse(if (type|. == "array" or . == "object") then .[] else empty end))|select(length > 0);
jq ´[paths]´
[1,[[],{"a":2}]]
=> [[0],[1],[1,0],[1,1],[1,1,"a"]]
-
leaf_paths¶
Outputs the paths to all the leaves (non-array, non-object elements) in its
input.
-
-
jq ´[leaf_paths]´
[1,[[],{"a":2}]]
=> [[0],[1,1,"a"]]
-
add¶
The filter
add takes as input an array, and produces as output the
elements of the array added together. This might mean summed, concatenated or
merged depending on the types of the elements of the input array - the rules
are the same as those for the
+ operator (described above).
If the input is an empty array,
add returns
null.
-
-
jq ´add´
["a","b","c"]
=> "abc"
jq ´add´
[1, 2, 3]
=> 6
jq ´add´
[]
=> null
-
any¶
The filter
any takes as input an array of boolean values, and produces
true as output if any of the the elements of the array is
true.
If the input is an empty array,
any returns
false.
-
-
jq ´any´
[true, false]
=> true
jq ´any´
[false, false]
=> false
jq ´any´
[]
=> false
-
all¶
The filter
all takes as input an array of boolean values, and produces
true as output if all of the the elements of the array are
true.
If the input is an empty array,
all returns
true.
-
-
jq ´all´
[true, false]
=> false
jq ´all´
[true, true]
=> true
jq ´all´
[]
=> true
-
range¶
The
range function produces a range of numbers.
range(4;10)
produces 6 numbers, from 4 (inclusive) to 10 (exclusive). The numbers are
produced as separate outputs. Use
[range(4;10)] to get a range as an
array.
-
-
jq ´range(2;4)´
null
=> 2, 3
jq ´[range(2;4)]´
null
=> [2,3]
-
floor¶
The
floor function returns the floor of its numeric input.
-
-
jq ´floor´
3.14159
=> 3
-
sqrt¶
The
sqrt function returns the square root of its numeric input.
-
-
jq ´sqrt´
9
=> 3
-
tonumber¶
The
tonumber function parses its input as a number. It will convert
correctly-formatted strings to their numeric equivalent, leave numbers alone,
and give an error on all other input.
-
-
jq ´.[] | tonumber´
[1, "1"]
=> 1, 1
-
tostring¶
The
tostring function prints its input as a string. Strings are left
unchanged, and all other values are JSON-encoded.
-
-
jq ´.[] | tostring´
[1, "1", [1]]
=> "1", "1", "[1]"
-
type¶
The
type function returns the type of its argument as a string, which is
one of null, boolean, number, string, array or object.
-
-
jq ´map(type)´
[0, false, [], {}, null, "hello"]
=> ["number", "boolean", "array", "object", "null", "string"]
-
sort, sort_by¶
The
sort functions sorts its input, which must be an array. Values are
sorted in the following order:
- •
- null
- •
- false
- •
- true
- •
- numbers
- •
- strings, in alphabetical order (by unicode codepoint
value)
- •
- arrays, in lexical order
- •
- objects
-
The ordering for objects is a little complex: first they´re compared by
comparing their sets of keys (as arrays in sorted order), and if their keys
are equal then the values are compared key by key.
sort_by may be used to sort by a particular field of an object, or by
applying any jq filter.
sort_by(foo) compares two elements by comparing
the result of
foo on each element.
-
-
jq ´sort´
[8,3,null,6]
=> [null,3,6,8]
jq ´sort_by(.foo)´
[{"foo":4, "bar":10}, {"foo":3, "bar":100}, {"foo":2, "bar":1}]
=> [{"foo":2, "bar":1}, {"foo":3, "bar":100}, {"foo":4, "bar":10}]
-
group_by¶
group_by(.foo) takes as input an array, groups the elements having the
same
.foo field into separate arrays, and produces all of these arrays
as elements of a larger array, sorted by the value of the
.foo field.
Any jq expression, not just a field access, may be used in place of
.foo.
The sorting order is the same as described in the
sort function above.
-
-
jq ´group_by(.foo)´
[{"foo":1, "bar":10}, {"foo":3, "bar":100}, {"foo":1, "bar":1}]
=> [[{"foo":1, "bar":10}, {"foo":1, "bar":1}], [{"foo":3, "bar":100}]]
-
min, max, min_by, max_by¶
Find the minimum or maximum element of the input array. The
_by versions
allow you to specify a particular field or property to examine, e.g.
min_by(.foo) finds the object with the smallest
foo field.
-
-
jq ´min´
[5,4,2,7]
=> 2
jq ´max_by(.foo)´
[{"foo":1, "bar":14}, {"foo":2, "bar":3}]
=> {"foo":2, "bar":3}
-
unique¶
The
unique function takes as input an array and produces an array of the
same elements, in sorted order, with duplicates removed.
-
-
jq ´unique´
[1,2,5,3,5,3,1,3]
=> [1,2,3,5]
-
unique_by¶
The
unique_by(.foo) function takes as input an array and produces an
array of the same elements, in sorted order, with elqements with a duplicate
.foo field removed. Think of it as making an array by taking one
element out of every group produced by
group_by.
-
-
jq ´unique_by(.foo)´
[{"foo": 1, "bar": 2}, {"foo": 1, "bar": 3}, {"foo": 4, "bar": 5}]
=> [{"foo": 1, "bar": 2}, {"foo": 4, "bar": 5}]
jq ´unique_by(length)´
["chunky", "bacon", "kitten", "cicada", "asparagus"]
=> ["chunky", "bacon", "asparagus"]
-
reverse¶
This function reverses an array.
-
-
jq ´reverse´
[1,2,3,4]
=> [4,3,2,1]
-
contains¶
The filter
contains(b) will produce true if b is completely contained
within the input. A string B is contained in a string A if B is a substring of
A. An array B is contained in an array A is all elements in B are contained in
any element in A. An object B is contained in object A if all of the values in
B are contained in the value in A with the same key. All other types are
assumed to be contained in each other if they are equal.
-
-
jq ´contains("bar")´
"foobar"
=> true
jq ´contains(["baz", "bar"])´
["foobar", "foobaz", "blarp"]
=> true
jq ´contains(["bazzzzz", "bar"])´
["foobar", "foobaz", "blarp"]
=> false
jq ´contains({foo: 12, bar: [{barp: 12}]})´
{"foo": 12, "bar":[1,2,{"barp":12, "blip":13}]}
=> true
jq ´contains({foo: 12, bar: [{barp: 15}]})´
{"foo": 12, "bar":[1,2,{"barp":12, "blip":13}]}
=> false
-
indices(s)¶
Outputs an array containing the indices in
. where
s occurs. The
input may be an array, in which case if
s is an array then the indices
output will be those where all elements in
. match those of
s.
-
-
jq ´indices(", ")´
"a,b, cd, efg, hijk"
=> [3,7,12]
jq ´indices(1)´
[0,1,2,1,3,1,4]
=> [1,3,5]
jq ´indices([1,2])´
[0,1,2,3,1,4,2,5,1,2,6,7]
=> [1,8]
-
index(s), rindex(s)¶
Outputs the index of the first (
index) or last (
rindex)
occurrence of
s in the input.
-
-
jq ´index(", ")´
"a,b, cd, efg, hijk"
=> 3
jq ´rindex(", ")]´
"a,b, cd, efg, hijk"
=> 12
-
startswith¶
Outputs
true if . starts with the given string argument.
-
-
jq ´[.[]|startswith("foo")]´
["fo", "foo", "barfoo", "foobar", "barfoob"]
=> [false, true, false, true, false]
-
endswith¶
Outputs
true if . ends with the given string argument.
-
-
jq ´[.[]|endswith("foo")]´
["foobar", "barfoo"]
=> [false, true, true, false, false]
-
ltrimstr¶
Outputs its input with the given prefix string removed, if it starts with it.
-
-
jq ´[.[]|ltrimstr("foo")]´
["fo", "foo", "barfoo", "foobar", "afoo"]
=> ["fo","","barfoo","bar","afoo"]
-
rtrimstr¶
Outputs its input with the given suffix string removed, if it starts with it.
-
-
jq ´[.[]|rtrimstr("foo")]´
["fo", "foo", "barfoo", "foobar", "foob"]
=> ["fo","","bar","foobar","foob"]
-
explode¶
Converts an input string into an array of the string´s codepoint numbers.
-
-
jq ´explode´
"foobar"
=> [102,111,111,98,97,114]
-
implode¶
The inverse of explode.
-
-
jq ´implode´
[65, 66, 67]
=> "ABC"
-
split¶
Splits an input string on the separator argument.
-
-
jq ´split(", ")´
"a, b,c,d, e"
=> ["a","b,c,d","e"]
-
join¶
Joins the array of elements given as input, using the argument as separator. It
is the inverse of
split: that is, running
split("foo") |
join("foo") over any input string returns said input string.
-
-
jq ´join(", ")´
["a","b,c,d","e"]
=> "a, b,c,d, e"
-
recurse¶
The
recurse function allows you to search through a recursive structure,
and extract interesting data from all levels. Suppose your input represents a
filesystem:
-
-
{"name": "/", "children": [
{"name": "/bin", "children": [
{"name": "/bin/ls", "children": []},
{"name": "/bin/sh", "children": []}]},
{"name": "/home", "children": [
{"name": "/home/stephen", "children": [
{"name": "/home/stephen/jq", "children": []}]}]}]}
-
Now suppose you want to extract all of the filenames present. You need to
retrieve
.name,
.children[].name,
.children[].children[].name, and so on. You can do this with:
-
-
recurse(.children[]) | .name
jq ´recurse(.foo[])´
{"foo":[{"foo": []}, {"foo":[{"foo":[]}]}]}
=> {"foo":[{"foo":[]},{"foo":[{"foo":[]}]}]}, {"foo":[]}, {"foo":[{"foo":[]}]}, {"foo":[]}
-
recurse_down¶
A quieter version of
recurse(.[]), equivalent to:
-
-
def recurse_down: recurse(.[]?);
-
Short-hand for
recurse_down. This is intended to resemble the XPath
// operator. Note that
..a does not work; use
..|a
instead.
-
-
jq ´..|.a?´
[[{"a":1}]]
=> 1
-
String interpolation - \(foo)¶
Inside a string, you can put an expression inside parens after a backslash.
Whatever the expression returns will be interpolated into the string.
-
-
jq ´"The input was \(.), which is one less than \(.+1)"´
42
=> "The input was 42, which is one less than 43"
-
Convert to/from JSON¶
The
tojson and
fromjson builtins dump values as JSON texts or
parse JSON texts into values, respectively. The tojson builtin differs from
tostring in that tostring returns strings unmodified, while tojson encodes
strings as JSON strings.
-
-
jq ´[.[]|tostring]´
[1, "foo", ["foo"]]
=> ["1","foo","[\"foo\"]"]
jq ´[.[]|tojson]´
[1, "foo", ["foo"]]
=> ["1","\"foo\"","[\"foo\"]"]
jq ´[.[]|tojson|fromjson]´
[1, "foo", ["foo"]]
=> [1,"foo",["foo"]]
-
The
@foo syntax is used to format and escape strings, which is useful for
building URLs, documents in a language like HTML or XML, and so forth.
@foo can be used as a filter on its own, the possible escapings are:
- @text:
- Calls tostring, see that function for details.
- @json:
- Serialises the input as JSON.
- @html:
- Applies HTML/XML escaping, by mapping the characters
<>&´" to their entity equivalents
<, >, &, ',
".
- @uri:
- Applies percent-encoding, by mapping all reserved URI
characters to a %xx sequence.
- @csv:
- The input must be an array, and it is rendered as CSV with
double quotes for strings, and quotes escaped by repetition.
- @sh:
- The input is escaped suitable for use in a command-line for
a POSIX shell. If the input is an array, the output will be a series of
space-separated strings.
- @base64:
- The input is converted to base64 as specified by RFC
4648.
This syntax can be combined with string interpolation in a useful way. You can
follow a
@foo token with a string literal. The contents of the string
literal will
not be escaped. However, all interpolations made inside
that string literal will be escaped. For instance,
-
-
@uri "http://www.google.com/search?q=\(.search)"
-
will produce the following output for the input
{"search":"what is jq?"}:
-
-
"http://www.google.com/search?q=what%20is%20jq%3f"
-
Note that the slashes, question mark, etc. in the URL are not escaped, as they
were part of the string literal.
-
-
jq ´@html´
"This works if x < y"
=> "This works if x < y"
jq ´@sh "echo \(.)"´
"O´Hara´s Ale"
=> "echo ´O´\\´´Hara´\\´´s Ale´"
-
CONDITIONALS AND COMPARISONS¶
==, !=¶
The expression ´a == b´ will produce ´true´ if the result of
a and b are equal (that is, if they represent equivalent JSON documents) and
´false´ otherwise. In particular, strings are never considered equal
to numbers. If you´re coming from Javascript, jq´s == is like
Javascript´s === - considering values equal only when they have the same
type as well as the same value.
!= is "not equal", and ´a != b´ returns the opposite value
of ´a == b´
-
-
jq ´.[] == 1´
[1, 1.0, "1", "banana"]
=> true, true, false, false
-
if-then-else¶
if A then B else C end will act the same as
B if
A produces
a value other than false or null, but act the same as
C otherwise.
Checking for false or null is a simpler notion of "truthiness" than is
found in Javascript or Python, but it means that you´ll sometimes have to
be more explicit about the condition you want: you can´t test whether,
e.g. a string is empty using
if .name then A else B end, you´ll
need something more like
if (.name | length) > 0 then A else B end
instead.
If the condition A produces multiple results, it is considered "true"
if any of those results is not false or null. If it produces zero results,
it´s considered false.
More cases can be added to an if using
elif A then B syntax.
-
-
jq ´if . == 0 then
-
"zero" elif . == 1 then "one" else "many"
end´
-
-
2
=> "many"
-
>, >=, <=, <¶
The comparison operators
>,
>=,
<=,
<
return whether their left argument is greater than, greater than or equal to,
less than or equal to or less than their right argument (respectively).
The ordering is the same as that described for
sort, above.
-
-
jq ´. < 5´
2
=> true
-
and/or/not¶
jq supports the normal Boolean operators and/or/not. They have the same standard
of truth as if expressions - false and null are considered "false
values", and anything else is a "true value".
If an operand of one of these operators produces multiple results, the operator
itself will produce a result for each input.
not is in fact a builtin function rather than an operator, so it is
called as a filter to which things can be piped rather than with special
syntax, as in
.foo and .bar | not.
These three only produce the values "true" and "false", and
so are only useful for genuine Boolean operations, rather than the common
Perl/Python/Ruby idiom of "value_that_may_be_null or default". If
you want to use this form of "or", picking between two values rather
than evaluating a condition, see the "//" operator below.
-
-
jq ´42 and "a string"´
null
=> true
jq ´(true, false) or false´
null
=> true, false
jq ´(true, true) and (true, false)´
null
=> true, false, true, false
jq ´[true, false | not]´
null
=> [false, true]
-
Alternative operator - //¶
A filter of the form
a // b produces the same results as
a, if
a produces results other than
false and
null. Otherwise,
a // b produces the same results as
b.
This is useful for providing defaults:
.foo // 1 will evaluate to
1 if there´s no
.foo element in the input. It´s
similar to how
or is sometimes used in Python (jq´s
or
operator is reserved for strictly Boolean operations).
-
-
jq ´.foo // 42´
{"foo": 19}
=> 19
jq ´.foo // 42´
{}
=> 42
-
ADVANCED FEATURES¶
Variables are an absolute necessity in most programming languages, but
they´re relegated to an "advanced feature" in jq.
In most languages, variables are the only means of passing around data. If you
calculate a value, and you want to use it more than once, you´ll need to
store it in a variable. To pass a value to another part of the program,
you´ll need that part of the program to define a variable (as a function
parameter, object member, or whatever) in which to place the data.
It is also possible to define functions in jq, although this is is a feature
whose biggest use is defining jq´s standard library (many jq functions
such as
map and
find are in fact written in jq).
Finally, jq has a
reduce operation, which is very powerful but a bit
tricky. Again, it´s mostly used internally, to define some useful bits of
jq´s standard library.
Variables¶
In jq, all filters have an input and an output, so manual plumbing is not
necessary to pass a value from one part of a program to the next. Many
expressions, for instance
a + b, pass their input to two distinct
subexpressions (here
a and
b are both passed the same input), so
variables aren´t usually necessary in order to use a value twice.
For instance, calculating the average value of an array of numbers requires a
few variables in most languages - at least one to hold the array, perhaps one
for each element or for a loop counter. In jq, it´s simply
add /
length - the
add expression is given the array and produces its
sum, and the
length expression is given the array and produces its
length.
So, there´s generally a cleaner way to solve most problems in jq than
defining variables. Still, sometimes they do make things easier, so jq lets
you define variables using
expression as $variable. All variable names
start with
$. Here´s a slightly uglier version of the
array-averaging example:
-
-
length as $array_length | add / $array_length
-
We´ll need a more complicated problem to find a situation where using
variables actually makes our lives easier.
Suppose we have an array of blog posts, with "author" and
"title" fields, and another object which is used to map author
usernames to real names. Our input looks like:
-
-
{"posts": [{"title": "Frist psot", "author": "anon"},
{"title": "A well-written article", "author": "person1"}],
"realnames": {"anon": "Anonymous Coward",
"person1": "Person McPherson"}}
-
We want to produce the posts with the author field containing a real name, as
in:
-
-
{"title": "Frist psot", "author": "Anonymous Coward"}
{"title": "A well-written article", "author": "Person McPherson"}
-
We use a variable, $names, to store the realnames object, so that we can refer
to it later when looking up author usernames:
-
-
.realnames as $names | .posts[] | {title, author: $names[.author]}
-
The expression
exp as $x | ... means: for each value of expression
exp, run the rest of the pipeline with the entire original input, and
with
$x set to that value. Thus
as functions as something of a
foreach loop.
Variables are scoped over the rest of the expression that defines them, so
-
-
.realnames as $names | (.posts[] | {title, author: $names[.author]})
-
will work, but
-
-
(.realnames as $names | .posts[]) | {title, author: $names[.author]}
-
won´t.
-
-
jq ´.bar as $x | .foo | . + $x´
{"foo":10, "bar":200}
=> 210
-
Defining Functions¶
You can give a filter a name using "def" syntax:
-
-
def increment: . + 1;
-
From then on,
increment is usable as a filter just like a builtin
function (in fact, this is how some of the builtins are defined). A function
may take arguments:
-
-
def map(f): [.[] | f];
-
Arguments are passed as filters, not as values. The same argument may be
referenced multiple times with different inputs (here
f is run for each
element of the input array). Arguments to a function work more like callbacks
than like value arguments.
If you want the value-argument behaviour for defining simple functions, you can
just use a variable:
-
-
def addvalue(f): f as $value | map(. + $value);
-
With that definition,
addvalue(.foo) will add the current input´s
.foo field to each element of the array.
-
-
jq ´def addvalue(f): . + [f]; map(addvalue(.[0]))´
[[1,2],[10,20]]
=> [[1,2,1], [10,20,10]]
jq ´def addvalue(f): f as $x | map(. + $x); addvalue(.[0])´
[[1,2],[10,20]]
=> [[1,2,1,2], [10,20,1,2]]
-
Reduce¶
The
reduce syntax in jq allows you to combine all of the results of an
expression by accumulating them into a single answer. As an example,
we´ll pass
[3,2,1] to this expression:
-
-
reduce .[] as $item (0; . + $item)
-
For each result that
.[] produces,
. + $item is run to accumulate
a running total, starting from 0. In this example,
.[] produces the
results 3, 2, and 1, so the effect is similar to running something like this:
-
-
0 | (3 as $item | . + $item) |
(2 as $item | . + $item) |
(1 as $item | . + $item)
jq ´reduce .[] as $item (0; . + $item)´
[10,2,5,3]
=> 20
-
ASSIGNMENT¶
Assignment works a little differently in jq than in most programming languages.
jq doesn´t distinguish between references to and copies of something -
two objects or arrays are either equal or not equal, without any further
notion of being "the same object" or "not the same
object".
If an object has two fields which are arrays,
.foo and
.bar, and
you append something to
.foo, then
.bar will not get bigger.
Even if you´ve just set
.bar = .foo. If you´re used to
programming in languages like Python, Java, Ruby, Javascript, etc. then you
can think of it as though jq does a full deep copy of every object before it
does the assignment (for performance, it doesn´t actually do that, but
that´s the general idea).
The filter
.foo = 1 will take as input an object and produce as output an
object with the "foo" field set to 1. There is no notion of
"modifying" or "changing" something in jq - all jq values
are immutable. For instance,
.foo = .bar | .foo.baz = 1
will not have the side-effect of setting .bar.baz to be set to 1, as the
similar-looking program in Javascript, Python, Ruby or other languages would.
Unlike these languages (but like Haskell and some other functional languages),
there is no notion of two arrays or objects being "the same array"
or "the same object". They can be equal, or not equal, but if we
change one of them in no circumstances will the other change behind our backs.
This means that it´s impossible to build circular values in jq (such as an
array whose first element is itself). This is quite intentional, and ensures
that anything a jq program can produce can be represented in JSON.
As well as the assignment operator ´=´, jq provides the
"update" operator ´|=´, which takes a filter on the
right-hand side and works out the new value for the property being assigned to
by running the old value through this expression. For instance, .foo |= .+1
will build an object with the "foo" field set to the input´s
"foo" plus 1.
This example should show the difference between ´=´ and
´|=´:
Provide input ´{"a": {"b": 10}, "b":
20}´ to the programs:
.a = .b .a |= .b
The former will set the "a" field of the input to the "b"
field of the input, and produce the output {"a": 20}. The latter
will set the "a" field of the input to the "a"
field´s "b" field, producing {"a": 10}.
+=, -=, *=, /=, %=, //=¶
jq has a few operators of the form
a op= b, which are all equivalent to
a |= . op b. So,
+= 1 can be used to increment values.
-
-
jq ´.foo += 1´
{"foo": 42}
=> {"foo": 43}
-
Complex assignments¶
Lots more things are allowed on the left-hand side of a jq assignment than in
most langauges. We´ve already seen simple field accesses on the left hand
side, and it´s no surprise that array accesses work just as well:
-
-
.posts[0].title = "JQ Manual"
-
What may come as a surprise is that the expression on the left may produce
multiple results, referring to different points in the input document:
-
-
.posts[].comments |= . + ["this is great"]
-
That example appends the string "this is great" to the
"comments" array of each post in the input (where the input is an
object with a field "posts" which is an array of posts).
When jq encounters an assignment like ´a = b´, it records the
"path" taken to select a part of the input document while executing
a. This path is then used to find which part of the input to change while
executing the assignment. Any filter may be used on the left-hand side of an
equals - whichever paths it selects from the input will be where the
assignment is performed.
This is a very powerful operation. Suppose we wanted to add a comment to blog
posts, using the same "blog" input above. This time, we only want to
comment on the posts written by "stedolan". We can find those posts
using the "select" function described earlier:
-
-
.posts[] | select(.author == "stedolan")
-
The paths provided by this operation point to each of the posts that
"stedolan" wrote, and we can comment on each of them in the same way
that we did before:
-
-
(.posts[] | select(.author == "stedolan") | .comments) |=
. + ["terrible."]
-
BUGS¶
Presumably. Report them or discuss them at:
-
-
https://github.com/stedolan/jq/issues
-
AUTHOR¶
Stephen Dolan
<mu@netsoc.tcd.ie>