JQ(1) JQ(1)
NAME
jq – Command-line JSON processor
SYNOPSIS
jq [options…] filter [files…]
jq can transform JSON in various ways, by selecting, iterating, reduc‐
ing 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.
jq can accept text input as well, but by default, jq reads a stream of
JSON entities (including numbers and other literals) from stdin. White‐
space is only needed to separate entities such as 1 and 2, and true and
false. 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 con‐
cern input and output formatting. The filter is written in the jq lan‐
guage and specifies how to transform the input file or 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 stan‐
dard 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 out‐
put. 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 then performing the division.
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.
· –seq:
Use the application/json-seq MIME type scheme for separating JSON
texts in jq´s input and output. This means that an ASCII RS (record
separator) character is printed before each value on output and an
ASCII LF (line feed) is printed after every output. Input JSON
texts that fail to parse are ignored (but warned about), discarding
all subsequent input until the next RS. This mode also parses the
output of jq without the –seq option.
· –stream:
Parse the input in streaming fashion, outputing arrays of path and
leaf values (scalars and empty arrays or empty objects). For exam‐
ple, “a” becomes [[],”a”], and [[],”a”,[“b”]] becomes [[0],[]],
[[1],”a”], and [[1,0],”b”].
This is useful for processing very large inputs. Use this in con‐
junction with filtering and the reduce and foreach syntax to reduce
large inputs incrementally.
· –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.
· –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 calcu‐
lator 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.
· –tab:
Use a tab for each indentation level instead of two spaces.
· –indent n:
Use the given number of spaces (no more than 8) for indentation.
· –color-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.
Colors can be configured with the JQ_COLORS environment variable
(see below).
· –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 fil‐
ters talk to non-JSON-based systems.
· –join-output / -j:
Like -r but jq won´t print a newline after each output.
· -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.
· -Ldirectory / -L directory:
Prepend directory to the search list for modules. If this option is
used then no builtin search list is used. See the section on mod‐
ules below.
· -e / –exit-status:
Sets the exit status of jq to 0 if the last output values was nei‐
ther 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.
Another way to set the exit status is with the halt_error builtin
function.
· –arg name value:
This option passes a value to the jq program as a predefined vari‐
able. If you run jq with –arg foo bar, then $foo is available in
the program and has the value “bar”. Note that value will be
treated as a string, so –arg foo 123 will bind $foo to “123”.
Named arguments are also available to the jq program as
$ARGS.named.
· –argjson name JSON-text:
This option passes a JSON-encoded value to the jq program as a pre‐
defined variable. If you run jq with –argjson foo 123, then $foo
is available in the program and has the value 123.
· –slurpfile variable-name filename:
This option reads all the JSON texts in the named file and binds an
array of the parsed JSON values to the given global variable. If
you run jq with –argfile foo bar, then $foo is available in the
program and has an array whose elements correspond to the texts in
the file named bar.
· –argfile variable-name filename:
Do not use. Use –slurpfile instead.
(This option is like –slurpfile, but when the file has just one
text, then that is used, else an array of texts is used as in
–slurpfile.)
· –args:
Remaining arguments are positional string arguments. These are
available to the jq program as $ARGS.positional[].
· –jsonargs:
Remaining arguments are positional JSON text arguments. These are
available to the jq program as $ARGS.positional[].
· –run-tests [filename]:
Runs the tests in the given file or standard input. This must be
the last option given and does not honor all preceding options. The
input consists of comment lines, empty lines, and program lines
followed by one input line, as many lines of output as are expected
(one per output), and a terminating empty line. Compilation failure
tests start with a line containing only “%%FAIL”, then a line con‐
taining the program to compile, then a line containing an error
message to compare to the actual.
Be warned that this option can change backwards-incompatibly.
BASIC FILTERS
Identity: .
The absolute simplest filter is . . This is a filter that takes its
input and produces it unchanged as output. That is, this is the iden‐
tity operator.
Since jq by default pretty-prints all output, this trivial program can
be a useful way of formatting JSON output from, say, curl.
jq ´.´
“Hello, world!”
=> “Hello, world!”
Object Identifier-Index: .foo, .foo.bar
The simplest useful filter is .foo. When given a JSON object (aka dic‐
tionary or hash) as input, it produces the value at the key “foo”, or
null if there´s none present.
A filter of the form .foo.bar is equivalent to .foo|.bar.
This syntax only works for simple, identifier-like keys, that is, keys
that are all made of alphanumeric characters and underscore, and which
do not start with a digit.
If the key contains special characters, you need to surround it with
double quotes like this: .”foo$”, or else .[“foo$”].
For example .[“foo::bar”] and .[“foo.bar”] work while .foo::bar does
not, and .foo.bar means .[“foo”].[“bar”].
jq ´.foo´
{“foo”: 42, “bar”: “less interesting data”}
=> 42
jq ´.foo´
{“notfoo”: true, “alsonotfoo”: false}
=> null
jq ´.[“foo”]´
{“foo”: 42}
=> 42
Optional Object Identifier-Index: .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]
=> []
Generic Object Index: .[
You can also look up fields of an object using syntax like .[“foo”]
(.foo above is a shorthand version of this, but only for identi‐
fier-like strings).
Array Index: .[2]
When the index value is an integer, .[
are zero-based, so .[2] returns the third element.
Negative indices are allowed, with -1 referring to the last element, -2
referring to the next to last element, and so on.
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]´
[1,2,3]
=> 2
Array/String Slice: .[10:15]
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).
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”]
Array/Object Value Iterator: .[]
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.
Comma: ,
If two filters are separated by a comma, then the same input will be
fed into both and the two filters´ output value streams will be con‐
catenated in order: 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”
Pipe: |
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.
Note that .a.b.c is the same as .a | .b | .c.
Note too that . is the input value at the particular stage in a “pipe‐
line”, specifically: where the . expression appears. Thus .a | . | .b
is the same as .a.b, as the . in the middle refers to whatever value .a
produced.
jq ´.[] | .name´
[{“name”:”JSON”, “good”:true}, {“name”:”XML”, “good”:false}]
=> “JSON”, “XML”
Parenthesis
Parenthesis work as a grouping operator just as in any typical program‐
ming language.
jq ´(. + 2) * 5´
1
=> 15
TYPES AND VALUES
jq supports the same set of datatypes as JSON – numbers, strings, bool‐
eans, 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, including a pipeline. 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 [] oper‐
ator (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”]
jq ´[ .[] | . * 2]´
[1, 2, 3]
=> [2, 4, 6]
Object Construction: {}
Like JSON, {} is for constructing objects (aka dictionaries or hashes),
as in: {“a”: 42, “b”: 17}.
If the keys are “identifier-like”, then the quotes can be left off, as
in {a:42, b:17}. Keys generated by expressions need to be parenthe‐
sized, e.g., {(“a”+”b”):59}.
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} as its input. You can use this to select particu‐
lar 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 is so common, there´s a shortcut syntax for it: {user,
title}.
If one of the expressions produces multiple results, multiple dictio‐
naries 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”]}
Recursive Descent: ..
Recursively descends ., producing every value. This is the same as the
zero-argument recurse builtin (see below). This is intended to resemble
the XPath // operator. Note that ..a does not work; use ..|.a instead.
In the example below we use ..|.a? to find all the values of object
keys “a” in any object found “below” ..
This is particularly useful in conjunction with path(EXP) (also see
below) and the ? operator.
jq ´..|.a?´
[[{“a”:1}]]
=> 1
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 occurrences of the second array´s ele‐
ments from the first array.
jq ´4 – .a´
{“a”:3}
=> 1
jq ´. – [“xml”, “yaml”]´
[“xml”, “yaml”, “json”]
=> [“json”]
Multiplication, division, modulo: *, /, and %
These infix operators behave as expected when given two numbers. Divi‐
sion by zero raises an error. x % y computes x modulo y.
Multiplying a string by a number produces the concatenation of that
string that many times. “x” * 0 produces null.
Dividing a string by another splits the first using the second as sepa‐
rators.
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}}
jq ´.[] | (1 / .)?´
[1,0,-1]
=> 1, -1
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 con‐
tains (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
utf8bytelength
The builtin function utf8bytelength outputs the number of bytes used to
encode a string in UTF-8.
jq ´utf8bytelength´
“\u03bc”
=> 2
keys, keys_unsorted
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.
The keys_unsorted function is just like keys, but if the input is an
object then the keys will not be sorted, instead the keys will roughly
be in insertion order.
jq ´keys´
{“abc”: 1, “abcd”: 2, “Foo”: 3}
=> [“Foo”, “abc”, “abcd”]
jq ´keys´
[42,3,35]
=> [0,1,2]
has(key)
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]
in
The builtin function in returns whether or not the input key is in the
given object, or the input index corresponds to an element in the given
array. It is, essentially, an inversed version of has.
jq ´.[] | in({“foo”: 42})´
[“foo”, “bar”]
=> true, false
jq ´map(in([0,1]))´
[2, 0]
=> [false, true]
map(x), map_values(x)
For any filter x, map(x) will run that filter for each element of the
input array, and return the outputs in a new array. map(.+1) will
increment each element of an array of numbers.
Similarly, map_values(x) will run that filter for each element, but it
will return an object when an object is passed.
map(x) is equivalent to [.[] | x]. In fact, this is how it´s defined.
Similarly, map_values(x) is defined as .[] |= x.
jq ´map(.+1)´
[1,2,3]
=> [2,3,4]
jq ´map_values(.+1)´
{“a”: 1, “b”: 2, “c”: 3}
=> {“a”: 2, “b”: 3, “c”: 4}
path(path_expression)
Outputs array representations of the given path expression in .. The
outputs are arrays of strings (object keys) and/or numbers (array
indices).
Path expressions are jq expressions like .a, but also .[]. There are
two types of path expressions: ones that can match exactly, and ones
that cannot. For example, .a.b.c is an exact match path expression,
while .a[].b is not.
path(exact_path_expression) will produce the array representation of
the path expression even if it does not exist in ., if . is null or an
array or an object.
path(pattern) will produce array representations of the paths matching
pattern if the paths exist in ..
Note that the path expressions are not different from normal expres‐
sions. The expression path(..|select(type==”boolean”)) outputs all the
paths to boolean values in ., and only those paths.
jq ´path(.a[0].b)´
null
=> [“a”,0,”b”]
jq ´[path(..)]´
{“a”:[{“b”:1}]}
=> [[],[“a”],[“a”,0],[“a”,0,”b”]]
del(path_expression)
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”]
getpath(PATHS)
The builtin function getpath outputs the values in . found at each path
in PATHS.
jq ´getpath([“a”,”b”])´
null
=> null
jq ´[getpath([“a”,”b”], [“a”,”c”])]´
{“a”:{“b”:0, “c”:1}}
=> [0, 1]
setpath(PATHS; VALUE)
The builtin function setpath sets the PATHS in . to VALUE.
jq ´setpath([“a”,”b”]; 1)´
null
=> {“a”: {“b”: 1}}
jq ´setpath([“a”,”b”]; 1)´
{“a”:{“b”:0}}
=> {“a”: {“b”: 1}}
jq ´setpath([0,”a”]; 1)´
null
=> [{“a”:1}]
delpaths(PATHS)
The builtin function delpaths sets the PATHS in .. PATHS must be an
array of paths, where each path is an array of strings and numbers.
jq ´delpaths([[“a”,”b”]])´
{“a”:{“b”:1},”x”:{“y”:2}}
=> {“a”:{},”x”:{“y”:2}}
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. from_entries
accepts key, Key, name, Name, value and Value as keys.
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(boolean_expression)
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]
jq ´.[] | select(.id == “second”)´
[{“id”: “first”, “val”: 1}, {“id”: “second”, “val”: 2}]
=> {“id”: “second”, “val”: 2}
arrays, objects, iterables, booleans, numbers, normals, finites, strings,
nulls, values, scalars
These built-ins select only inputs that are arrays, objects, iterables
(arrays or objects), booleans, numbers, normal numbers, finite 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]
error(message)
Produces an error, just like .a applied to values other than null and
objects would, but with the given message as the error´s value. Errors
can be caught with try/catch; see below.
halt
Stops the jq program with no further outputs. jq will exit with exit
status 0.
halt_error, halt_error(exit_code)
Stops the jq program with no further outputs. The input will be printed
on stderr as raw output (i.e., strings will not have double quotes)
with no decoration, not even a newline.
The given exit_code (defaulting to 5) will be jq´s exit status.
For example, “Error: somthing went wrong\n”|halt_error(1).
$__loc__
Produces an object with a “file” key and a “line” key, with the file‐
name and line number where $__loc__ occurs, as values.
jq ´try error(“\($__loc__)”) catch .´
null
=> “{\”file\”:\”
paths, paths(node_filter), leaf_paths
paths outputs the paths to all the elements in its input (except it
does not output the empty list, representing . itself).
paths(f) outputs the paths to any values for which f is true. That is,
paths(numbers) outputs the paths to all numeric values.
leaf_paths is an alias of paths(scalars); leaf_paths is deprecated and
will be removed in the next major release.
jq ´[paths]´
[1,[[],{“a”:2}]]
=> [[0],[1],[1,0],[1,1],[1,1,”a”]]
jq ´[paths(scalars)]´
[1,[[],{“a”:2}]]
=> [[0],[1,1,”a”]]
add
The filter add takes as input an array, and produces as output the ele‐
ments 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, any(condition), any(generator; condition)
The filter any takes as input an array of boolean values, and produces
true as output if any of the elements of the array are true.
If the input is an empty array, any returns false.
The any(condition) form applies the given condition to the elements of
the input array.
The any(generator; condition) form applies the given condition to all
the outputs of the given generator.
jq ´any´
[true, false]
=> true
jq ´any´
[false, false]
=> false
jq ´any´
[]
=> false
all, all(condition), all(generator; condition)
The filter all takes as input an array of boolean values, and produces
true as output if all of the elements of the array are true.
The all(condition) form applies the given condition to the elements of
the input array.
The all(generator; condition) form applies the given condition to all
the outputs of the given generator.
If the input is an empty array, all returns true.
jq ´all´
[true, false]
=> false
jq ´all´
[true, true]
=> true
jq ´all´
[]
=> true
flatten, flatten(depth)
The filter flatten takes as input an array of nested arrays, and pro‐
duces a flat array in which all arrays inside the original array have
been recursively replaced by their values. You can pass an argument to
it to specify how many levels of nesting to flatten.
flatten(2) is like flatten, but going only up to two levels deep.
jq ´flatten´
[1, [2], [[3]]]
=> [1, 2, 3]
jq ´flatten(1)´
[1, [2], [[3]]]
=> [1, 2, [3]]
jq ´flatten´
[[]]
=> []
jq ´flatten´
[{“foo”: “bar”}, [{“foo”: “baz”}]]
=> [{“foo”: “bar”}, {“foo”: “baz”}]
range(upto), range(from;upto) range(from;upto;by)
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.
The one argument form generates numbers from 0 to the given number,
with an increment of 1.
The two argument form generates numbers from from to upto with an
increment of 1.
The three argument form generates numbers from to upto with an incre‐
ment of by.
jq ´range(2;4)´
null
=> 2, 3
jq ´[range(4)]´
null
=> [0,1,2,3]
jq ´[range(0;10;3)]´
null
=> [0,3,6,9]
jq ´[range(0;10;-1)]´
null
=> []
jq ´[range(0;-5;-1)]´
null
=> [0,-1,-2,-3,-4]
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”]
infinite, nan, isinfinite, isnan, isfinite, isnormal
Some arithmetic operations can yield infinities and “not a number”
(NaN) values. The isinfinite builtin returns true if its input is infi‐
nite. The isnan builtin returns true if its input is a NaN. The infi‐
nite builtin returns a positive infinite value. The nan builtin returns
a NaN. The isnormal builtin returns true if its input is a normal num‐
ber.
Note that division by zero raises an error.
Currently most arithmetic operations operating on infinities, NaNs, and
sub-normals do not raise errors.
jq ´.[] | (infinite * .) < 0´ [-1, 1] => true, false
jq ´infinite, nan | type´
null
=> “number”, “number”
sort, sort_by(path_expression)
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 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(path_expression)
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(path_exp), max_by(path_exp)
Find the minimum or maximum element of the input array.
The min_by(path_exp) and max_by(path_exp) functions allow you to spec‐
ify 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, unique_by(path_exp)
The unique function takes as input an array and produces an array of
the same elements, in sorted order, with duplicates removed.
The unique_by(path_exp) function will keep only one element for each
value obtained by applying the argument. Think of it as making an array
by taking one element out of every group produced by group.
jq ´unique´
[1,2,5,3,5,3,1,3]
=> [1,2,3,5]
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”]
=> [“bacon”, “chunky”, “asparagus”]
reverse
This function reverses an array.
jq ´reverse´
[1,2,3,4]
=> [4,3,2,1]
contains(element)
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 sub‐
string of A. An array B is contained in an array A if 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
inside
The filter inside(b) will produce true if the input is completely con‐
tained within b. It is, essentially, an inversed version of contains.
jq ´inside(“foobar”)´
“bar”
=> true
jq ´inside([“foobar”, “foobaz”, “blarp”])´
[“baz”, “bar”]
=> true
jq ´inside([“foobar”, “foobaz”, “blarp”])´
[“bazzzzz”, “bar”]
=> false
jq ´inside({“foo”: 12, “bar”:[1,2,{“barp”:12, “blip”:13}]})´
{“foo”: 12, “bar”: [{“barp”: 12}]}
=> true
jq ´inside({“foo”: 12, “bar”:[1,2,{“barp”:12, “blip”:13}]})´
{“foo”: 12, “bar”: [{“barp”: 15}]}
=> false
startswith(str)
Outputs true if . starts with the given string argument.
jq ´[.[]|startswith(“foo”)]´
[“fo”, “foo”, “barfoo”, “foobar”, “barfoob”]
=> [false, true, false, true, false]
endswith(str)
Outputs true if . ends with the given string argument.
jq ´[.[]|endswith(“foo”)]´
[“foobar”, “barfoo”]
=> [false, true]
combinations, combinations(n)
Outputs all combinations of the elements of the arrays in the input
array. If given an argument n, it outputs all combinations of n repeti‐
tions of the input array.
jq ´combinations´
[[1,2], [3, 4]]
=> [1, 3], [1, 4], [2, 3], [2, 4]
jq ´combinations(2)´
[0, 1]
=> [0, 0], [0, 1], [1, 0], [1, 1]
ltrimstr(str)
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(str)
Outputs its input with the given suffix string removed, if it ends 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 num‐
bers.
jq ´explode´
“foobar”
=> [102,111,111,98,97,114]
implode
The inverse of explode.
jq ´implode´
[65, 66, 67]
=> “ABC”
split(str)
Splits an input string on the separator argument.
jq ´split(“, “)´
“a, b,c,d, e, ”
=> [“a”,”b,c,d”,”e”,””]
join(str)
Joins the array of elements given as input, using the argument as sepa‐
rator. It is the inverse of split: that is, running split(“foo”) |
join(“foo”) over any input string returns said input string.
Numbers and booleans in the input are converted to strings. Null values
are treated as empty strings. Arrays and objects in the input are not
supported.
jq ´join(“, “)´
[“a”,”b,c,d”,”e”]
=> “a, b,c,d, e”
jq ´join(” “)´
[“a”,1,2.3,true,null,false]
=> “a 1 2.3 true false”
ascii_downcase, ascii_upcase
Emit a copy of the input string with its alphabetic characters (a-z and
A-Z) converted to the specified case.
while(cond; update)
The while(cond; update) function allows you to repeatedly apply an
update to . until cond is false.
Note that while(cond; update) is internally defined as a recursive jq
function. Recursive calls within while will not consume additional mem‐
ory if update produces at most one output for each input. See advanced
topics below.
jq ´[while(.<100; .*2)]´ 1 => [1,2,4,8,16,32,64]
until(cond; next)
The until(cond; next) function allows you to repeatedly apply the
expression next, initially to . then to its own output, until cond is
true. For example, this can be used to implement a factorial function
(see below).
Note that until(cond; next) is internally defined as a recursive jq
function. Recursive calls within until() will not consume additional
memory if next produces at most one output for each input. See advanced
topics below.
jq ´[.,1]|until(.[0] < 1; [.[0] - 1, .[1] * .[0]])|.[1]´ 4 => 24
recurse(f), recurse, recurse(f; condition), recurse_down
The recurse(f) function allows you to search through a recursive struc‐
ture, 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
When called without an argument, recurse is equivalent to
recurse(.[]?).
recurse(f) is identical to recurse(f; . != null) and can be used with‐
out concerns about recursion depth.
recurse(f; condition) is a generator which begins by emitting . and
then emits in turn .|f, .|f|f, .|f|f|f, … so long as the computed
value satisfies the condition. For example, to generate all the inte‐
gers, at least in principle, one could write recurse(.+1; true).
For legacy reasons, recurse_down exists as an alias to calling recurse
without arguments. This alias is considered deprecated and will be
removed in the next major release.
The recursive calls in recurse will not consume additional memory when‐
ever f produces at most a single output for each input.
jq ´recurse(.foo[])´
{“foo”:[{“foo”: []}, {“foo”:[{“foo”:[]}]}]}
=> {“foo”:[{“foo”:[]},{“foo”:[{“foo”:[]}]}]}, {“foo”:[]}, {“foo”:[{“foo”:[]}]}, {“foo”:[]}
jq ´recurse´
{“a”:0,”b”:[1]}
=> {“a”:0,”b”:[1]}, 0, [1], 1
jq ´recurse(. * .; . < 20)´ 2 => 2, 4, 16
walk(f)
The walk(f) function applies f recursively to every component of the
input entity. When an array is encountered, f is first applied to its
elements and then to the array itself; when an object is encountered, f
is first applied to all the values and then to the object. In practice,
f will usually test the type of its input, as illustrated in the fol‐
lowing examples. The first example highlights the usefulness of pro‐
cessing the elements of an array of arrays before processing the array
itself. The second example shows how all the keys of all the objects
within the input can be considered for alteration.
jq ´walk(if type == “array” then sort else . end)´
[[4, 1, 7], [8, 5, 2], [3, 6, 9]]
=> [[1,4,7],[2,5,8],[3,6,9]]
jq ´walk( if type == “object” then with_entries( .key |= sub( “^_+”; “”) ) else . end )´
[ { “_a”: { “__b”: 2 } } ]
=> [{“a”:{“b”:2}}]
$ENV, env
$ENV is an object representing the environment variables as set when
the jq program started.
env outputs an object representing jq´s current environment.
At the moment there is no builtin for setting environment variables.
jq ´$ENV.PAGER´
null
=> “less”
jq ´env.PAGER´
null
=> “less”
transpose
Transpose a possibly jagged matrix (an array of arrays). Rows are
padded with nulls so the result is always rectangular.
jq ´transpose´
[[1], [2,3]]
=> [[1,2],[null,3]]
bsearch(x)
bsearch(x) conducts a binary search for x in the input array. If the
input is sorted and contains x, then bsearch(x) will return its index
in the array; otherwise, if the array is sorted, it will return (-1 –
ix) where ix is an insertion point such that the array would still be
sorted after the insertion of x at ix. If the array is not sorted,
bsearch(x) will return an integer that is probably of no interest.
jq ´bsearch(0)´
[0,1]
=> 0
jq ´bsearch(0)´
[1,2,3]
=> -1
jq ´bsearch(4) as $ix | if $ix < 0 then .[-(1+$ix)] = 4 else . end´ [1,2,3] => [1,2,3,4]
String interpolation – \(foo)
Inside a string, you can put an expression inside parens after a back‐
slash. 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”]]
=> [1,”foo”,[“foo”]]
Format strings and escaping
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:
Serializes 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 dou‐
ble quotes for strings, and quotes escaped by repetition.
@tsv:
The input must be an array, and it is rendered as TSV (tab-sepa‐
rated values). Each input array will be printed as a single
line. Fields are separated by a single tab (ascii 0x09). Input
characters line-feed (ascii 0x0a), carriage-return (ascii 0x0d),
tab (ascii 0x09) and backslash (ascii 0x5c) will be output as
escape sequences \n, \r, \t, \\ respectively.
@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.
@base64d:
The inverse of @base64, input is decoded as specified by RFC
4648. Note: If the decoded string is not UTF-8, the results are
undefined.
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 “https://www.google.com/search?q=\(.search)”
will produce the following output for the input {“search”:”what is
jq?”}:
“https://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´”
jq ´@base64´
“This is a message”
=> “VGhpcyBpcyBhIG1lc3NhZ2U=”
jq ´@base64d´
“VGhpcyBpcyBhIG1lc3NhZ2U=”
=> “This is a message”
Dates
jq provides some basic date handling functionality, with some
high-level and low-level builtins. In all cases these builtins deal
exclusively with time in UTC.
The fromdateiso8601 builtin parses datetimes in the ISO 8601 format to
a number of seconds since the Unix epoch (1970-01-01T00:00:00Z). The
todateiso8601 builtin does the inverse.
The fromdate builtin parses datetime strings. Currently fromdate only
supports ISO 8601 datetime strings, but in the future it will attempt
to parse datetime strings in more formats.
The todate builtin is an alias for todateiso8601.
The now builtin outputs the current time, in seconds since the Unix
epoch.
Low-level jq interfaces to the C-library time functions are also pro‐
vided: strptime, strftime, strflocaltime, mktime, gmtime, and local‐
time. Refer to your host operating system´s documentation for the for‐
mat strings used by strptime and strftime. Note: these are not neces‐
sarily stable interfaces in jq, particularly as to their localization
functionality.
The gmtime builtin consumes a number of seconds since the Unix epoch
and outputs a “broken down time” representation of Greenwhich Meridian
time as an array of numbers representing (in this order): the year, the
month (zero-based), the day of the month (one-based), the hour of the
day, the minute of the hour, the second of the minute, the day of the
week, and the day of the year — all one-based unless otherwise stated.
The day of the week number may be wrong on some systems for dates
before March 1st 1900, or after December 31 2099.
The localtime builtin works like the gmtime builtin, but using the
local timezone setting.
The mktime builtin consumes “broken down time” representations of time
output by gmtime and strptime.
The strptime(fmt) builtin parses input strings matching the fmt argu‐
ment. The output is in the “broken down time” representation consumed
by gmtime and output by mktime.
The strftime(fmt) builtin formats a time (GMT) with the given format.
The strflocaltime does the same, but using the local timezone setting.
The format strings for strptime and strftime are described in typical C
library documentation. The format string for ISO 8601 datetime is
“%Y-%m-%dT%H:%M:%SZ”.
jq may not support some or all of this date functionality on some sys‐
tems. In particular, the %u and %j specifiers for strptime(fmt) are not
supported on macOS.
jq ´fromdate´
“2015-03-05T23:51:47Z”
=> 1425599507
jq ´strptime(“%Y-%m-%dT%H:%M:%SZ”)´
“2015-03-05T23:51:47Z”
=> [2015,2,5,23,51,47,4,63]
jq ´strptime(“%Y-%m-%dT%H:%M:%SZ”)|mktime´
“2015-03-05T23:51:47Z”
=> 1425599507
SQL-Style Operators
jq provides a few SQL-style operators.
INDEX(stream; index_expression):
This builtin produces an object whose keys are computed by the
given index expression applied to each value from the given
stream.
JOIN($idx; stream; idx_expr; join_expr):
This builtin joins the values from the given stream to the given
index. The index´s keys are computed by applying the given index
expression to each value from the given stream. An array of the
value in the stream and the corresponding value from the index
is fed to the given join expression to produce each result.
JOIN($idx; stream; idx_expr):
Same as JOIN($idx; stream; idx_expr; .).
JOIN($idx; idx_expr):
This builtin joins the input . to the given index, applying the
given index expression to . to compute the index key. The join
operation is as described above.
IN(s):
This builtin outputs true if . appears in the given stream, oth‐
erwise it outputs false.
IN(source; s):
This builtin outputs true if any value in the source stream
appears in the second stream, otherwise it outputs false.
builtins
Returns a list of all builtin functions in the format name/arity. Since
functions with the same name but different arities are considered sepa‐
rate functions, all/0, all/1, and all/2 would all be present in the
list.
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, then B is evaluated once
for each result that is not false or null, and C is evaluated once for
each false or null.
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 argu‐ ment 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 spe‐
cial 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 pro‐
duces 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 some‐
times used in Python (jq´s or operator is reserved for strictly Boolean
operations).
jq ´.foo // 42´
{“foo”: 19}
=> 19
jq ´.foo // 42´
{}
=> 42
try-catch
Errors can be caught by using try EXP catch EXP. The first expression
is executed, and if it fails then the second is executed with the error
message. The output of the handler, if any, is output as if it had been
the output of the expression to try.
The try EXP form uses empty as the exception handler.
jq ´try .a catch “. is not an object”´
true
=> “. is not an object”
jq ´[.[]|try .a]´
[{}, true, {“a”:1}]
=> [null, 1]
jq ´try error(“some exception”) catch .´
true
=> “some exception”
Breaking out of control structures
A convenient use of try/catch is to break out of control structures
like reduce, foreach, while, and so on.
For example:
# Repeat an expression until it raises “break” as an
# error, then stop repeating without re-raising the error.
# But if the error caught is not “break” then re-raise it.
try repeat(exp) catch .==”break” then empty else error;
jq has a syntax for named lexical labels to “break” or “go (back) to”:
label $out | … break $out …
The break $label_name expression will cause the program to to act as
though the nearest (to the left) label $label_name produced empty.
The relationship between the break and corresponding label is lexical:
the label has to be “visible” from the break.
To break out of a reduce, for example:
label $out | reduce .[] as $item (null; if .==false then break $out else … end)
The following jq program produces a syntax error:
break $out
because no label $out is visible.
Error Suppression / Optional Operator: ?
The ? operator, used as EXP?, is shorthand for try EXP.
jq ´[.[]|(.a)?]´
[{}, true, {“a”:1}]
=> [null, 1]
REGULAR EXPRESSIONS (PCRE)
jq uses the Oniguruma regular expression library, as do php, ruby,
TextMate, Sublime Text, etc, so the description here will focus on jq
specifics.
The jq regex filters are defined so that they can be used using one of
these patterns:
STRING | FILTER( REGEX )
STRING | FILTER( REGEX; FLAGS )
STRING | FILTER( [REGEX] )
STRING | FILTER( [REGEX, FLAGS] )
where: * STRING, REGEX and FLAGS are jq strings and subject to jq
string interpolation; * REGEX, after string interpolation, should be a
valid PCRE regex; * FILTER is one of test, match, or capture, as
described below.
FLAGS is a string consisting of one of more of the supported flags:
· g – Global search (find all matches, not just the first)
· i – Case insensitive search
· m – Multi line mode (´.´ will match newlines)
· n – Ignore empty matches
· p – Both s and m modes are enabled
· s – Single line mode (´^´ -> ´\A´, ´$´ -> ´\Z´)
· l – Find longest possible matches
· x – Extended regex format (ignore whitespace and comments)
To match whitespace in an x pattern use an escape such as \s, e.g.
· test( “a\sb”, “x” ).
Note that certain flags may also be specified within REGEX, e.g.
· jq -n ´(“test”, “TEst”, “teST”, “TEST”) | test( “(?i)te(?-i)st” )´
evaluates to: true, true, false, false.
test(val), test(regex; flags)
Like match, but does not return match objects, only true or false for
whether or not the regex matches the input.
jq ´test(“foo”)´
“foo”
=> true
jq ´.[] | test(“a b c # spaces are ignored”; “ix”)´
[“xabcd”, “ABC”]
=> true, true
match(val), match(regex; flags)
match outputs an object for each match it finds. Matches have the fol‐
lowing fields:
· offset – offset in UTF-8 codepoints from the beginning of the input
· length – length in UTF-8 codepoints of the match
· string – the string that it matched
· captures – an array of objects representing capturing groups.
Capturing group objects have the following fields:
· offset – offset in UTF-8 codepoints from the beginning of the input
· length – length in UTF-8 codepoints of this capturing group
· string – the string that was captured
· name – the name of the capturing group (or null if it was unnamed)
Capturing groups that did not match anything return an offset of -1
jq ´match(“(abc)+”; “g”)´
“abc abc”
=> {“offset”: 0, “length”: 3, “string”: “abc”, “captures”: [{“offset”: 0, “length”: 3, “string”: “abc”, “name”: null}]}, {“offset”: 4, “length”: 3, “string”: “abc”, “captures”: [{“offset”: 4, “length”: 3, “string”: “abc”, “name”: null}]}
jq ´match(“foo”)´
“foo bar foo”
=> {“offset”: 0, “length”: 3, “string”: “foo”, “captures”: []}
jq ´match([“foo”, “ig”])´
“foo bar FOO”
=> {“offset”: 0, “length”: 3, “string”: “foo”, “captures”: []}, {“offset”: 8, “length”: 3, “string”: “FOO”, “captures”: []}
jq ´match(“foo (?
“foo bar foo foo foo”
=> {“offset”: 0, “length”: 11, “string”: “foo bar foo”, “captures”: [{“offset”: 4, “length”: 3, “string”: “bar”, “name”: “bar123”}]}, {“offset”: 12, “length”: 8, “string”: “foo foo”, “captures”: [{“offset”: -1, “length”: 0, “string”: null, “name”: “bar123”}]}
jq ´[ match(“.”; “g”)] | length´
“abc”
=> 3
capture(val), capture(regex; flags)
Collects the named captures in a JSON object, with the name of each
capture as the key, and the matched string as the corresponding value.
jq ´capture(“(?[a-z]+)-(?
“xyzzy-14”
=> { “a”: “xyzzy”, “n”: “14” }
scan(regex), scan(regex; flags)
Emit a stream of the non-overlapping substrings of the input that match
the regex in accordance with the flags, if any have been specified. If
there is no match, the stream is empty. To capture all the matches for
each input string, use the idiom [ expr ], e.g. [ scan(regex) ].
split(regex; flags)
For backwards compatibility, split splits on a string, not a regex.
splits(regex), splits(regex; flags)
These provide the same results as their split counterparts, but as a
stream instead of an array.
sub(regex; tostring) sub(regex; string; flags)
Emit the string obtained by replacing the first match of regex in the
input string with tostring, after interpolation. tostring should be a
jq string, and may contain references to named captures. The named cap‐
tures are, in effect, presented as a JSON object (as constructed by
capture) to tostring, so a reference to a captured variable named “x”
would take the form: “(.x)”.
gsub(regex; string), gsub(regex; string; flags)
gsub is like sub but all the non-overlapping occurrences of the regex
are replaced by the string, after interpolation.
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).
jq has reduction operators, which are very powerful but a bit tricky.
Again, these are mostly used internally, to define some useful bits of
jq´s standard library.
It may not be obvious at first, but jq is all about generators (yes, as
often found in other languages). Some utilities are provided to help
deal with generators.
Some minimal I/O support (besides reading JSON from standard input, and
writing JSON to standard output) is available.
Finally, there is a module/library system.
Variable / Symbolic Binding Operator: … as $identifier | …
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 vari‐
ables 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 pro‐
duces its sum, and the length expression is given the array and pro‐
duces 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-aver‐
aging 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
$x set to that value. Thus as functions as something of a foreach loop.
Just as {foo} is a handy way of writing {foo: .foo}, so {$foo} is a
handy way of writing {foo:$foo}.
Multiple variables may be declared using a single as expression by pro‐
viding a pattern that matches the structure of the input (this is known
as “destructuring”):
. as {realnames: $names, posts: [$first, $second]} | …
The variable declarations in array patterns (e.g., . as [$first, $sec‐
ond]) bind to the elements of the array in from the element at index
zero on up, in order. When there is no value at the index for an array
pattern element, null is bound to that variable.
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.
For programming language theorists, it´s more accurate to say that jq
variables are lexically-scoped bindings. In particular there´s no way
to change the value of a binding; one can only setup a new binding with
the same name, but which will not be visible where the old one was.
jq ´.bar as $x | .foo | . + $x´
{“foo”:10, “bar”:200}
=> 210
jq ´. as $i|[(.*2|. as $i| $i), $i]´
5
=> [10,5]
jq ´. as [$a, $b, {c: $c}] | $a + $b + $c´
[2, 3, {“c”: 4, “d”: 5}]
=> 9
jq ´.[] as [$a, $b] | {a: $a, b: $b}´
[[0], [0, 1], [2, 1, 0]]
=> {“a”:0,”b”:null}, {“a”:0,”b”:1}, {“a”:2,”b”:1}
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 func‐
tion (in fact, this is how many of the builtins are defined). A func‐
tion may take arguments:
def map(f): [.[] | f];
Arguments are passed as filters (functions with no arguments), not as
values. The same argument may be referenced multiple times with differ‐
ent inputs (here f is run for each element of the input array). Argu‐
ments to a function work more like callbacks than like value arguments.
This is important to understand. Consider:
def foo(f): f|f;
5|foo(.*2)
The result will be 20 because f is .*2, and during the first invocation
of f . will be 5, and the second time it will be 10 (5 * 2), so the
result will be 20. Function arguments are filters, and filters expect
an input when invoked.
If you want the value-argument behaviour for defining simple functions,
you can just use a variable:
def addvalue(f): f as $f | map(. + $f);
Or use the short-hand:
def addvalue($f): …;
With either definition, addvalue(.foo) will add the current input´s
.foo field to each element of the array. Do note that calling
addvalue(.[]) will cause the map(. + $f) part to be evaluated once per
value in the value of . at the call site.
Multiple definitions using the same function name are allowed. Each
re-definition replaces the previous one for the same number of function
arguments, but only for references from functions (or main program)
subsequent to the re-definition. See also the section below on scoping.
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]]
Scoping
There are two types of symbols in jq: value bindings (a.k.a., “vari‐
ables”), and functions. Both are scoped lexically, with expressions
being able to refer only to symbols that have been defined “to the
left” of them. The only exception to this rule is that functions can
refer to themselves so as to be able to create recursive functions.
For example, in the following expression there is a binding which is
visible “to the right” of it, … | .*3 as $times_three | [. +
$times_three] | …, but not “to the left”. Consider this expression
now, … | (.*3 as $times_three | [.+ $times_three]) | …: here the
binding $times_three is not visible past the closing parenthesis.
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
isempty(exp)
Returns true if exp produces no outputs, false otherwise.
jq ´isempty(empty)´
null
=> true
limit(n; exp)
The limit function extracts up to n outputs from exp.
jq ´[limit(3;.[])]´
[0,1,2,3,4,5,6,7,8,9]
=> [0,1,2]
first(expr), last(expr), nth(n; expr)
The first(expr) and last(expr) functions extract the first and last
values from expr, respectively.
The nth(n; expr) function extracts the nth value output by expr. This
can be defined as def nth(n; expr): last(limit(n + 1; expr));. Note
that nth(n; expr) doesn´t support negative values of n.
jq ´[first(range(.)), last(range(.)), nth(./2; range(.))]´
10
=> [0,9,5]
first, last, nth(n)
The first and last functions extract the first and last values from any
array at ..
The nth(n) function extracts the nth value of any array at ..
jq ´[range(.)]|[first, last, nth(5)]´
10
=> [0,9,5]
foreach
The foreach syntax is similar to reduce, but intended to allow the con‐
struction of limit and reducers that produce intermediate results (see
example).
The form is foreach EXP as $var (INIT; UPDATE; EXTRACT). Like reduce,
INIT is evaluated once to produce a state value, then each output of
EXP is bound to $var, UPDATE is evaluated for each output of EXP with
the current state and with $var visible. Each value output by UPDATE
replaces the previous state. Finally, EXTRACT is evaluated for each new
state to extract an output of foreach.
This is mostly useful only for constructing reduce- and limit-like
functions. But it is much more general, as it allows for partial reduc‐
tions (see the example below).
jq ´[foreach .[] as $item ([[],[]]; if $item == null then [[],.[0]] else [(.[0] + [$item]),[]] end; if $item == null then .[1] else empty end)]´
[1,2,3,4,null,”a”,”b”,null]
=> [[1,2,3,4],[“a”,”b”]]
Recursion
As described above, recurse uses recursion, and any jq function can be
recursive. The while builtin is also implemented in terms of recursion.
Tail calls are optimized whenever the expression to the left of the
recursive call outputs its last value. In practice this means that the
expression to the left of the recursive call should not produce more
than one output for each input.
For example:
def recurse(f): def r: ., (f | select(. != null) | r); r;
def while(cond; update):
def _while:
if cond then ., (update | _while) else empty end;
_while;
def repeat(exp):
def _repeat:
exp, _repeat;
_repeat;
Generators and iterators
Some jq operators and functions are actually generators in that they
can produce zero, one, or more values for each input, just as one might
expect in other programming languages that have generators. For exam‐
ple, .[] generates all the values in its input (which must be an array
or an object), range(0; 10) generates the integers between 0 and 10,
and so on.
Even the comma operator is a generator, generating first the values
generated by the expression to the left of the comma, then for each of
those, the values generate by the expression on the right of the comma.
The empty builtin is the generator that produces zero outputs. The
empty builtin backtracks to the preceding generator expression.
All jq functions can be generators just by using builtin generators. It
is also possible to define new generators using only recursion and the
comma operator. If the recursive call(s) is(are) “in tail position”
then the generator will be efficient. In the example below the recur‐
sive call by _range to itself is in tail position. The example shows
off three advanced topics: tail recursion, generator construction, and
sub-functions.
jq ´def range(init; upto; by): def _range: if (by > 0 and . < upto) or (by < 0 and . > upto) then ., ((.+by)|_range) else . end; if by == 0 then init else init|_range end | select((by > 0 and . < upto) or (by < 0 and . > upto)); range(0; 10; 3)´
null
=> 0, 3, 6, 9
jq ´def while(cond; update): def _while: if cond then ., (update | _while) else empty end; _while; [while(.<100; .*2)]´ 1 => [1,2,4,8,16,32,64]
MATH
jq currently only has IEEE754 double-precision (64-bit) floating point
number support.
Besides simple arithmetic operators such as +, jq also has most stan‐
dard math functions from the C math library. C math functions that take
a single input argument (e.g., sin()) are available as zero-argument jq
functions. C math functions that take two input arguments (e.g., pow())
are available as two-argument jq functions that ignore .. C math func‐
tions that take three input arguments are available as three-argument
jq functions that ignore ..
Availability of standard math functions depends on the availability of
the corresponding math functions in your operating system and C math
library. Unavailable math functions will be defined but will raise an
error.
One-input C math functions: acos acosh asin asinh atan atanh cbrt ceil
cos cosh erf erfc exp exp10 exp2 expm1 fabs floor gamma j0 j1 lgamma
log log10 log1p log2 logb nearbyint pow10 rint round significand sin
sinh sqrt tan tanh tgamma trunc y0 y1.
Two-input C math functions: atan2 copysign drem fdim fmax fmin fmod
frexp hypot jn ldexp modf nextafter nexttoward pow remainder scalb
scalbln yn.
Three-input C math functions: fma.
See your system´s manual for more information on each of these.
I/O
At this time jq has minimal support for I/O, mostly in the form of con‐
trol over when inputs are read. Two builtins functions are provided for
this, input and inputs, that read from the same sources (e.g., stdin,
files named on the command-line) as jq itself. These two builtins, and
jq´s own reading actions, can be interleaved with each other.
Two builtins provide minimal output capabilities, debug, and stderr.
(Recall that a jq program´s output values are always output as JSON
texts on stdout.) The debug builtin can have application-specific
behavior, such as for executables that use the libjq C API but aren´t
the jq executable itself. The stderr builtin outputs its input in raw
mode to stder with no additional decoration, not even a newline.
Most jq builtins are referentially transparent, and yield constant and
repeatable value streams when applied to constant inputs. This is not
true of I/O builtins.
input
Outputs one new input.
inputs
Outputs all remaining inputs, one by one.
This is primarily useful for reductions over a program´s inputs.
debug
Causes a debug message based on the input value to be produced. The jq
executable wraps the input value with [“DEBUG:”,
prints that and a newline on stderr, compactly. This may change in the
future.
stderr
Prints its input in raw and compact mode to stderr with no additional
decoration, not even a newline.
input_filename
Returns the name of the file whose input is currently being filtered.
Note that this will not work well unless jq is running in a UTF-8
locale.
input_line_number
Returns the line number of the input currently being filtered.
STREAMING
With the –stream option jq can parse input texts in a streaming fash‐
ion, allowing jq programs to start processing large JSON texts immedi‐
ately rather than after the parse completes. If you have a single JSON
text that is 1GB in size, streaming it will allow you to process it
much more quickly.
However, streaming isn´t easy to deal with as the jq program will have
[
Several builtins are provided to make handling streams easier.
The examples below use the streamed form of [0,[1]], which is
[[0],0],[[1,0],1],[[1,0]],[[1]].
Streaming forms include [
value, empty array, or empty object), and [
of an array or object). Future versions of jq run with –stream and
-seq may output additional forms such as [“error message”] when an
input text fails to parse.
truncate_stream(stream_expression)
Consumes a number as input and truncates the corresponding number of
path elements from the left of the outputs of the given streaming
expression.
jq ´[1|truncate_stream([[0],1],[[1,0],2],[[1,0]],[[1]])]´
1
=> [[[0],2],[[0]]]
fromstream(stream_expression)
Outputs values corresponding to the stream expression´s outputs.
jq ´fromstream(1|truncate_stream([[0],1],[[1,0],2],[[1,0]],[[1]]))´
null
=> [2]
tostream
The tostream builtin outputs the streamed form of its input.
jq ´. as $dot|fromstream($dot|tostream)|.==$dot´
[0,[1,{“a”:1},{“b”:2}]]
=> true
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, with‐
out 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
previously 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).
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.
All the assignment operators in jq have path expressions on the
left-hand side (LHS). The right-hand side (RHS) procides values to set
to the paths named by the LHS path expressions.
Values in jq are always immutable. Internally, assignment works by
using a reduction to compute new, replacement values for . that have
had all the desired assignments applied to ., then outputting the modi‐
fied value. This might be made clear by this example: {a:{b:{c:1}}} |
(.a.b|=3), .. This will output {“a”:{“b”:3}} and {“a”:{“b”:{“c”:1}}}
because the last sub-expression, ., sees the original value, not the
modified value.
Most users will want to use modification assignment operators, such as
|= or +=, rather than =.
Note that the LHS of assignment operators refers to a value in .. Thus
$var.foo = 1 won´t work as expected ($var.foo is not a valid or useful
path expression in .); use $var | .foo = 1 instead.
Note too that .a,.b=0 does not set .a and .b, but (.a,.b)=0 sets both.
Update-assignment: |=
This is the “update” operator ´|=´. It takes a filter on the right-hand
side and works out the new value for the property of . being assigned
to by running the old value through this expression. For instance,
(.foo, .bar) |= .+1 will build an object with the “foo” field set to
the input´s “foo” plus 1, and the “bar” field set to the input´s “bar”
plus 1.
The left-hand side can be any general path expression; see path().
Note that the left-hand side of ´|=´ refers to a value in .. Thus
$var.foo |= . + 1 won´t work as expected ($var.foo is not a valid or
useful path expression in .); use $var | .foo |= . + 1 instead.
If the right-hand side outputs no values (i.e., empty), then the
left-hand side path will be deleted, as with del(path).
If the right-hand side outputs multiple values, only the first one will
be used (COMPATIBILITY NOTE: in jq 1.5 and earlier releases, it used to
be that only the last one was used).
jq ´(..|select(type==”boolean”)) |= if . then 1 else 0 end´
[true,false,[5,true,[true,[false]],false]]
=> [1,0,[5,1,[1,[0]],0]]
Arithmetic update-assignment: +=, -=, *=, /=, %=, //=
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, being the same
as |= . + 1.
jq ´.foo += 1´
{“foo”: 42}
=> {“foo”: 43}
Plain assignment: =
This is the plain assignment operator. Unlike the others, the input to
the right-hand-side (RHS) is the same as the input to the
left-hand-side (LHS) rather than the value at the LHS path, and all
values output by the RHS will be used (as shown below).
If the RHS of ´=´ produces multiple values, then for each such value jq
will set the paths on the left-hand side to the value and then it will
output the modified .. For example, (.a,.b)=range(2) outputs
{“a”:0,”b”:0}, then {“a”:1,”b”:1}. The “update” assignment forms (see
above) do not do this.
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, “b”: 20}. The latter will set
the “a” field of the input to the “a” field´s “b” field, producing
{“a”: 10, “b”: 20}.
Another example of the difference between ´=´ and ´|=´:
null|(.a,.b)=range(3)
outputs ´{“a”:0,”b”:0}´, ´{“a”:1,”b”:1}´, and ´{“a”:2,”b”:2}´, while
null|(.a,.b)|=range(3)
outputs just ´{“a”:0,”b”:0}´.
Complex assignments
Lots more things are allowed on the left-hand side of a jq assignment
than in most languages. 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 pro‐
duce multiple results, referring to different points in the input docu‐
ment:
.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 exe‐
cuting 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.”]
MODULES
jq has a library/module system. Modules are files whose names end in
.jq.
Modules imported by a program are searched for in a default search path
(see below). The import and include directives allow the importer to
alter this path.
Paths in the a search path are subject to various substitutions.
For paths starting with “~/”, the user´s home directory is substituted
for “~”.
For paths starting with “$ORIGIN/”, the path of the jq executable is
substituted for “$ORIGIN”.
For paths starting with “./” or paths that are “.”, the path of the
including file is substituted for “.”. For top-level programs given on
the command-line, the current directory is used.
Import directives can optionally specify a search path to which the
default is appended.
The default search path is the search path given to the -L command-line
option, else [“~/.jq”, “$ORIGIN/../lib/jq”, “$ORIGIN/../lib”].
Null and empty string path elements terminate search path processing.
A dependency with relative path “foo/bar” would be searched for in
“foo/bar.jq” and “foo/bar/bar.jq” in the given search path. This is
intended to allow modules to be placed in a directory along with, for
example, version control files, README files, and so on, but also to
allow for single-file modules.
Consecutive components with the same name are not allowed to avoid
ambiguities (e.g., “foo/foo”).
For example, with -L$HOME/.jq a module foo can be found in
$HOME/.jq/foo.jq and $HOME/.jq/foo/foo.jq.
If “$HOME/.jq” is a file, it is sourced into the main program.
import RelativePathString as NAME [
Imports a module found at the given path relative to a directory in a
search path. A “.jq” suffix will be added to the relative path string.
The module´s symbols are prefixed with “NAME::”.
The optional metadata must be a constant jq expression. It should be an
object with keys like “homepage” and so on. At this time jq only uses
the “search” key/value of the metadata. The metadata is also made
available to users via the modulemeta builtin.
The “search” key in the metadata, if present, should have a string or
array value (array of strings); this is the search path to be prefixed
to the top-level search path.
include RelativePathString [
Imports a module found at the given path relative to a directory in a
search path as if it were included in place. A “.jq” suffix will be
added to the relative path string. The module´s symbols are imported
into the caller´s namespace as if the module´s content had been
included directly.
The optional metadata must be a constant jq expression. It should be an
object with keys like “homepage” and so on. At this time jq only uses
the “search” key/value of the metadata. The metadata is also made
available to users via the modulemeta builtin.
import RelativePathString as $NAME [
Imports a JSON file found at the given path relative to a directory in
a search path. A “.json” suffix will be added to the relative path
string. The file´s data will be available as $NAME::NAME.
The optional metadata must be a constant jq expression. It should be an
object with keys like “homepage” and so on. At this time jq only uses
the “search” key/value of the metadata. The metadata is also made
available to users via the modulemeta builtin.
The “search” key in the metadata, if present, should have a string or
array value (array of strings); this is the search path to be prefixed
to the top-level search path.
module
This directive is entirely optional. It´s not required for proper oper‐
ation. It serves only the purpose of providing metadata that can be
read with the modulemeta builtin.
The metadata must be a constant jq expression. It should be an object
with keys like “homepage”. At this time jq doesn´t use this metadata,
but it is made available to users via the modulemeta builtin.
modulemeta
Takes a module name as input and outputs the module´s metadata as an
object, with the module´s imports (including metadata) as an array
value for the “deps” key.
Programs can use this to query a module´s metadata, which they could
then use to, for example, search for, download, and install missing
dependencies.
COLORS
To configure alternative colors just set the JQ_COLORS environment
variable to colon-delimited list of partial terminal escape sequences
like “1;31”, in this order:
· color for null
· color for false
· color for true
· color for numbers
· color for strings
· color for arrays
· color for objects
The default color scheme is the same as setting “JQ_COL‐
ORS=1;30:0;39:0;39:0;39:0;32:1;39:1;39”.
This is not a manual for VT100/ANSI escapes. However, each of these
color specifications should consist of two numbers separated by a
semi-colon, where the first number is one of these:
· 1 (bright)
· 2 (dim)
· 4 (underscore)
· 5 (blink)
· 7 (reverse)
· 8 (hidden)
and the second is one of these:
· 30 (black)
· 31 (red)
· 32 (green)
· 33 (yellow)
· 34 (blue)
· 35 (magenta)
· 36 (cyan)
· 37 (white)
BUGS
Presumably. Report them or discuss them at:
https://github.com/stedolan/jq/issues
AUTHOR
Stephen Dolan
December 2017 JQ(1)
1 Comment
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