jq - Command-line JSON processor
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.
jq can accept text input as well, but by default,
jq reads a
stream of JSON entities (including numbers and other literals) from
stdin. Whitespace 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
concern input and output formatting. The
filter is written in the jq
language and specifies how to transform the input file or document.
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 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
example, "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 conjunction 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 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.
- ○
-
--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
filters 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 modules below.
- ○
-
-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.
- 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 variable. 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 predefined 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 --slurpfile foo bar, then $foo is available
in the program and has an array whose elements correspond to the texts in
the file named bar.
- ○
-
--rawfile variable-name filename:
- This option reads in the named file and binds its contents
to the given global variable. If you run jq with --rawfile foo bar,
then $foo is available in the program and has a string whose
contents are to the texs 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 $ARGS.positional[].
- ○
-
--run-tests [filename]:
- Runs the tests in the given file or standard input. This
must be the last option given and does not honor all preceding options.
The input consists of comment lines, empty lines, and program lines
followed by one input line, as many lines of output as are expected (one
per output), and a terminating empty line. Compilation failure tests start
with a line containing only "%%FAIL", then a line containing the
program to compile, then a line containing an error message to compare to
the actual.
- Be warned that this option can change
backwards-incompatibly.
-
The absolute simplest filter is
. . This is a filter that takes its input
and produces it unchanged as output. That is, this is the identity operator.
Since jq by default pretty-prints all output, this trivial program can be a
useful way of formatting JSON output from, say,
curl.
-
-
jq ´.´
"Hello, world!"
=> "Hello, world!"
-
The simplest
useful filter is
.foo. When given a JSON object (aka
dictionary or hash) as input, it produces the value at the key
"foo", or null if there´s none present.
A filter of the form
.foo.bar is equivalent to
.foo|.bar.
This syntax only works for simple, identifier-like keys, that is, keys that are
all made of alphanumeric characters and underscore, and which do not start
with a digit.
If the key contains special characters, you need to surround it with double
quotes like this:
."foo$", 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
-
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]
=> []
-
You can also look up fields of an object using syntax like
.["foo"] (.foo above is a shorthand version of this, but only
for identifier-like strings).
When the index value is an integer,
.[<value>] can index arrays.
Arrays 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
-
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"]
-
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 same input will be fed into
both and the two filters´ output value streams will be concatenated 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"
-
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
"pipeline", 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 work as a grouping operator just as in any typical programming
language.
-
-
jq ´(. + 2) * 5´
1
=> 15
-
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.
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
[] 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"]
jq ´[ .[] | . * 2]´
[1, 2, 3]
=> [2, 4, 6]
-
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
parenthesized, 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 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 is so common, there´s a shortcut syntax for it:
{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"]}
-
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
-
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.
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}
-
As well as normal arithmetic subtraction on numbers, the
- operator can
be used on arrays to remove all occurrences of the second array´s
elements from the first array.
-
-
jq ´4 - .a´
{"a":3}
=> 1
jq ´. - ["xml", "yaml"]´
["xml", "yaml", "json"]
=> ["json"]
-
These infix operators behave as expected when given two numbers. Division 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 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}}
jq ´.[] | (1 / .)?´
[1,0,-1]
=> 1, -1
-
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
-
The builtin function
utf8bytelength outputs the number of bytes used to
encode a string in UTF-8.
-
-
jq ´utf8bytelength´
"\u03bc"
=> 2
-
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]
-
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]
-
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]
-
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}
-
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 expressions. 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"]]
-
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"]
-
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]
-
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}]
-
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}}
-
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}
-
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}
-
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 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]
-
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.
Stops the jq program with no further outputs. jq will exit with exit status
0.
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).
Produces an object with a "file" key and a "line" key, with
the filename and line number where
$__loc__ occurs, as values.
-
-
jq ´try error("\($__loc__)") catch .´
null
=> "{\"file\":\"<top-level>\",\"line\":1}"
-
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"]]
-
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
-
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
-
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
-
The filter
flatten takes as input an array of nested arrays, and produces
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"}]
-
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
increment of
by.
-
-
jq ´range(2;4)´
null
=> 2, 3
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]
-
The
floor function returns the floor of its numeric input.
-
-
jq ´floor´
3.14159
=> 3
-
The
sqrt function returns the square root of its numeric input.
-
-
jq ´sqrt´
9
=> 3
-
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
-
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]"
-
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"]
-
Some arithmetic operations can yield infinities and "not a number"
(NaN) values. The
isinfinite builtin returns
true if its input
is infinite. The
isnan builtin returns
true if its input is a
NaN. The
infinite builtin returns a positive infinite value. The
nan builtin returns a NaN. The
isnormal builtin returns true if
its input is a normal number.
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"
-
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(.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}]]
-
Find the minimum or maximum element of the input array.
The
min_by(path_exp) and
max_by(path_exp) functions 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}
-
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"]
-
This function reverses an array.
-
-
jq ´reverse´
[1,2,3,4]
=> [4,3,2,1]
-
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 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
-
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]
-
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
-
The filter
inside(b) will produce true if the input is completely
contained 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
-
Outputs
true if . starts with the given string argument.
-
-
jq ´[.[]|startswith("foo")]´
["fo", "foo", "barfoo", "foobar", "barfoob"]
=> [false, true, false, true, false]
-
Outputs
true if . ends with the given string argument.
-
-
jq ´[.[]|endswith("foo")]´
["foobar", "barfoo"]
=> [false, true]
-
Outputs all combinations of the elements of the arrays in the input array. If
given an argument
n, it outputs all combinations of
n
repetitions 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]
-
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"]
-
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"]
-
Converts an input string into an array of the string´s codepoint numbers.
-
-
jq ´explode´
"foobar"
=> [102,111,111,98,97,114]
-
The inverse of explode.
-
-
jq ´implode´
[65, 66, 67]
=> "ABC"
-
Splits an input string on the separator argument.
-
-
jq ´split(", ")´
"a, b,c,d, e, "
=> ["a","b,c,d","e",""]
-
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.
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"
-
Emit a copy of the input string with its alphabetic characters (a-z and A-Z)
converted to the specified case.
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
memory 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]
-
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
-
The
recurse(f) 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
-
When called without an argument,
recurse is equivalent to
recurse(.[]?).
recurse(f) is identical to
recurse(f; . != null) and can be used
without 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 integers, 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
whenever
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
-
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 following examples. The
first example highlights the usefulness of processing 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}}]
-
$ENV is an object representing the environment variables as set when the
jq program started.
env outputs an object representing jq´s current environment.
At the moment there is no builtin for setting environment variables.
-
-
jq ´$ENV.PAGER´
null
=> "less"
jq ´env.PAGER´
null
=> "less"
-
Transpose 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) 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]
-
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"
-
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:
-
-
@json:
-
-
@html:
-
-
@uri:
-
-
@csv:
-
-
@tsv:
-
-
@sh:
-
-
@base64:
-
-
@base64d:
-
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"
-
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 provided:
strptime,
strftime,
strflocaltime,
mktime,
gmtime, and
localtime. Refer to your host operating
system´s documentation for the format strings used by
strptime
and
strftime. Note: these are not necessarily 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
argument. 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 systems. 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
-
jq provides a few SQL-style operators.
- INDEX(stream; index_expression):
-
- JOIN($idx; stream; idx_expr; join_expr):
-
- JOIN($idx; stream; idx_expr):
-
- JOIN($idx; idx_expr):
-
- IN(s):
-
- IN(source; s):
-
Returns a list of all builtin functions in the format
name/arity. Since
functions with the same name but different arities are considered separate
functions,
all/0,
all/1, and
all/2 would all be present
in the list.
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 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 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
-
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]
-
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
-
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"
-
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
$out is visible.
The
? operator, used as
EXP?, is shorthand for
try EXP.
-
-
jq ´[.[]|(.a)?]´
[{}, true, {"a":1}]
=> [null, 1]
-
jq uses the Oniguruma regular expression library, as do php, ruby, TextMate,
Sublime Text, etc, so the description here will focus on jq specifics.
The jq regex filters are defined so that they can be used using one of these
patterns:
-
-
STRING | FILTER( REGEX )
STRING | FILTER( REGEX; FLAGS )
STRING | FILTER( [REGEX] )
STRING | FILTER( [REGEX, FLAGS] )
-
where: * STRING, REGEX and FLAGS are jq strings and subject to jq string
interpolation; * REGEX, after string interpolation, should be a valid PCRE
regex; * FILTER is one of
test,
match, or
capture, as
described below.
FLAGS is a string consisting of one of more of the supported flags:
- ○
-
g - Global search (find all matches, not just the
first)
- ○
-
i - Case insensitive search
- ○
-
m - Multi line mode (´.´ will match
newlines)
- ○
-
n - Ignore empty matches
- ○
-
p - Both s and m modes are enabled
- ○
-
s - Single line mode (´^´ ->
´\A´, ´$´ -> ´\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.
- ○
-
-
evaluates to: true, true, false, false.
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 outputs an object for each match it finds. Matches have the
following 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 (?<bar123>bar)? foo"; "ig")´
"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
-
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>[a-z]+)-(?<n>[0-9]+)")´
"xyzzy-14"
=> { "a": "xyzzy", "n": "14" }
-
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) ].
For backwards compatibility,
split splits on a string, not a regex.
These provide the same results as their
split counterparts, but as a
stream instead of an array.
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 captures
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 is like
sub but all the non-overlapping occurrences of the
regex are replaced by the string, after interpolation.
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.
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
$x set to that value. Thus
as functions as something of a
foreach loop.
Just as
{foo} is a handy way of writing
{foo: .foo}, so
{$foo} is a handy way of writing
{foo:$foo}.
Multiple variables may be declared using a single
as expression by
providing 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,
$second]) 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: $b}´
[[0], [0, 1], [2, 1, 0]]
=> {"a":0,"b":null}, {"a":0,"b":1}, {"a":2,"b":1}
-
The destructuring alternative operator provides a concise mechanism for
destructuring an input that can take one of several forms.
Suppose we have an API that returns a list of resources and events associated
with them, and we want to get the user_id and timestamp of the first event for
each resource. The API (having been clumsily converted from XML) will only
wrap the events in an array if the resource has multiple events:
-
-
{"resources": [{"id": 1, "kind": "widget", "events": {"action": "create", "user_id": 1, "ts": 13}},
{"id": 2, "kind": "widget", "events": [{"action": "create", "user_id": 1, "ts": 14}, {"action": "destroy", "user_id": 1, "ts": 15}]}]}
-
We can use the destructuring alternative operator to handle this structural
change simply:
-
-
.resources[] as {$id, $kind, events: {$user_id, $ts}} ?// {$id, $kind, events: [{$user_id, $ts}]} | {$user_id, $kind, $id, $ts}
-
Or, if we aren´t sure if the input is an array of values or an object:
-
-
.[] as [$id, $kind, $user_id, $ts] ?// {$id, $kind, $user_id, $ts} | ...
-
Each alternative need not define all of the same variables, but all named
variables will be available to the subsequent expression. Variables not
matched in the alternative that succeeded will be
null:
-
-
.resources[] as {$id, $kind, events: {$user_id, $ts}} ?// {$id, $kind, events: [{$first_user_id, $first_ts}]} | {$user_id, $first_user_id, $kind, $id, $ts, $first_ts}
-
Additionally, if the subsequent expression returns an error, the alternative
operator will attempt to try the next binding. Errors that occur during the
final alternative are passed through.
-
-
[[3]] | .[] as [$a] ?// [$b] | if $a != null then error("err: \($a)") else {$a,$b} end
jq ´.[] as {$a, $b, c: {$d, $e}} ?// {$a, $b, c: [{$d, $e}]} | {$a, $b, $d, $e}´
[{"a": 1, "b": 2, "c": {"d": 3, "e": 4}}, {"a": 1, "b": 2, "c": [{"d": 3, "e": 4}]}]
=> {"a":1,"b":2,"d":3,"e":4}, {"a":1,"b":2,"d":3,"e":4}
jq ´.[] as {$a, $b, c: {$d}} ?// {$a, $b, c: [{$e}]} | {$a, $b, $d, $e}´
[{"a": 1, "b": 2, "c": {"d": 3, "e": 4}}, {"a": 1, "b": 2, "c": [{"d": 3, "e": 4}]}]
=> {"a":1,"b":2,"d":3,"e":null}, {"a":1,"b":2,"d":null,"e":4}
jq ´.[] as [$a] ?// [$b] | if $a != null then error("err: \($a)") else {$a,$b} end´
[[3]]
=> {"a":null,"b":3}
-
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 many of the builtins are defined). A function
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 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. 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]]
-
There are two types of symbols in jq: value bindings (a.k.a.,
"variables"), 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.
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
-
Returns true if
exp produces no outputs, false otherwise.
-
-
jq ´isempty(empty)´
null
=> true
-
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]
-
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]
-
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]
-
The
foreach syntax is similar to
reduce, but intended to allow the
construction 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 reductions
(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"]]
-
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;
-
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 example,
.[] 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 recursive 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]
-
jq currently only has IEEE754 double-precision (64-bit) floating point number
support.
Besides simple arithmetic operators such as
+, jq also has most standard
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
functions 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.
At this time jq has minimal support for I/O, mostly in the form of control 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.
Outputs one new input.
Outputs all remaining inputs, one by one.
This is primarily useful for reductions over a program´s inputs.
Causes a debug message based on the input value to be produced. The jq
executable wraps the input value with
["DEBUG:",
<input-value>] and prints that and a newline on stderr, compactly.
This may change in the future.
Prints its input in raw and compact mode to stderr with no additional
decoration, not even a newline.
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.
Returns the line number of the input currently being filtered.
With the
--stream option jq can parse input texts in a streaming fashion,
allowing jq programs to start processing large JSON texts immediately 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
[<path>, <leaf-value>] (and a few other forms) as inputs.
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
[<path>, <leaf-value>] (to indicate
any scalar value, empty array, or empty object), and
[<path>] (to
indicate the end 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.
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]]]
-
Outputs values corresponding to the stream expression´s outputs.
-
-
jq ´fromstream(1|truncate_stream([[0],1],[[1,0],2],[[1,0]],[[1]]))´
null
=> [2]
-
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 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 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) provides 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 modified
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.
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]]
-
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}
-
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.
Provide input ´{"a": {"b": 10}, "b":
20}´ to the programs:
.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}.
outputs ´{"a":0,"b":0}´,
´{"a":1,"b":1}´, and
´{"a":2,"b":2}´, while
outputs just ´{"a":0,"b":0}´.
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 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."]
-
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.
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.
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.
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.
This directive is entirely optional. It´s not required for proper
operation. 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.
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.
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_COLORS=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)
-
Presumably. Report them or discuss them at:
-
-
https://github.com/stedolan/jq/issues
-
Stephen Dolan
<[email protected]>