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---
headline: jq 1.5 Manual
history: |
*The manual for the development version of jq can be found
[here](/jq/manual).*
body: |
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:
manpage_intro: |
jq(1) -- Command-line JSON processor
====================================
## SYNOPSIS
`jq` [<options>...] <filter> [<files>...]
`jq` can transform JSON in various ways, by selecting, iterating,
reducing and otherwise mangling JSON documents. For instance,
running the command `jq 'map(.price) | add'` will take an array of
JSON objects as input and return the sum of their "price" fields.
`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.
## FILTERS
manpage_epilogue: |
## BUGS
Presumably. Report them or discuss them at:
https://github.com/stedolan/jq/issues
## AUTHOR
Stephen Dolan `<mu@netsoc.tcd.ie>`
sections:
- title: Invoking jq
body: |
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 more also parses the output of jq without the `--seq`
option.
* `--stream`:
Parse the input in streaming fashion, outputting 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 7) 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`.
* `--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.
* `--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"`.
* `--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
`$foo` is available in the program and has the value `123`.
* `--slurpfile variable-name filename`:
This option reads all the JSON texts in the named file and binds
an array of the parsed JSON values to the given global variable.
If you run jq with `--argfile foo bar`, then `$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`.)
* `--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.
- title: Basic filters
entries:
- title: "`.`"
body: |
The absolute simplest (and least interesting) filter
is `.`. This is a filter that takes its input and
produces it unchanged as output.
Since jq by default pretty-prints all output, this trivial
program can be a useful way of formatting JSON output from,
say, `curl`.
examples:
- program: '.'
input: '"Hello, world!"'
output: ['"Hello, world!"']
- title: "`.foo`, `.foo.bar`"
body: |
The simplest *useful* filter is `.foo`. When given a
JSON object (aka dictionary or hash) as input, it produces
the value at the key "foo", or null if there's none present.
If the key contains special characters or starts with a digit,
you need to surround it with double quotes like this: `."foo$"`.
A filter of the form `.foo.bar` is equivalent to `.foo|.bar`.
examples:
- program: '.foo'
input: '{"foo": 42, "bar": "less interesting data"}'
output: [42]
- program: '.foo'
input: '{"notfoo": true, "alsonotfoo": false}'
output: ['null']
- program: '.["foo"]'
input: '{"foo": 42}'
output: [42]
- title: "`.foo?`"
body: |
Just like `.foo`, but does not output even an error when `.`
is not an array or an object.
examples:
- program: '.foo?'
input: '{"foo": 42, "bar": "less interesting data"}'
output: [42]
- program: '.foo?'
input: '{"notfoo": true, "alsonotfoo": false}'
output: ['null']
- program: '.["foo"]?'
input: '{"foo": 42}'
output: [42]
- program: '[.foo?]'
input: '[1,2]'
output: ['[]']
- title: "`.[<string>]`, `.[2]`, `.[10:15]`"
body: |
You can also look up fields of an object using syntax like
`.["foo"]` (.foo above is a shorthand version of this). This
one works for arrays as well, if the key is an
integer. Arrays are zero-based (like javascript), so `.[2]`
returns the third element of the array.
The `.[10:15]` syntax can be used to return a subarray of an
array or substring of a string. The array returned by
`.[10:15]` will be of length 5, containing the elements from
index 10 (inclusive) to index 15 (exclusive). Either index may
be negative (in which case it counts backwards from the end of
the array), or omitted (in which case it refers to the start
or end of the array).
The `.[2]` syntax can be used to return the element at the
given index. Negative indices are allowed, with -1 referring
to the last element, -2 referring to the next to last element,
and so on.
The `.foo` syntax only works for simple keys i.e. keys that
are all alphanumeric characters. `.[<string>]` works with
keys that contain special characters such as colons and dots.
For example `.["foo::bar"]` and `.["foo.bar"]` work while
`.foo::bar` and `.foo.bar` would not.
The `?` "operator" can also be used with the slice operator,
as in `.[10:15]?`, which outputs values where the inputs are
slice-able.
examples:
- program: '.[0]'
input: '[{"name":"JSON", "good":true}, {"name":"XML", "good":false}]'
output: ['{"name":"JSON", "good":true}']
- program: '.[2]'
input: '[{"name":"JSON", "good":true}, {"name":"XML", "good":false}]'
output: ['null']
- program: '.[2:4]'
input: '["a","b","c","d","e"]'
output: ['["c", "d"]']
- program: '.[2:4]'
input: '"abcdefghi"'
output: ['"cd"']
- program: '.[:3]'
input: '["a","b","c","d","e"]'
output: ['["a", "b", "c"]']
- program: '.[-2:]'
input: '["a","b","c","d","e"]'
output: ['["d", "e"]']
- program: '.[-2]'
input: '[1,2,3]'
output: ['2']
- title: "`.[]`"
body: |
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.
examples:
- program: '.[]'
input: '[{"name":"JSON", "good":true}, {"name":"XML", "good":false}]'
output:
- '{"name":"JSON", "good":true}'
- '{"name":"XML", "good":false}'
- program: '.[]'
input: '[]'
output: []
- program: '.[]'
input: '{"a": 1, "b": 1}'
output: ['1', '1']
- title: "`.[]?`"
body: |
Like `.[]`, but no errors will be output if . is not an array
or object.
- title: "`,`"
body: |
If two filters are separated by a comma, then the
input will be fed into both and there will be multiple
outputs: first, all of the outputs produced by the left
expression, and then all of the outputs produced by the
right. For instance, filter `.foo, .bar`, produces
both the "foo" fields and "bar" fields as separate outputs.
examples:
- program: '.foo, .bar'
input: '{"foo": 42, "bar": "something else", "baz": true}'
output: ['42', '"something else"']
- program: ".user, .projects[]"
input: '{"user":"stedolan", "projects": ["jq", "wikiflow"]}'
output: ['"stedolan"', '"jq"', '"wikiflow"']
- program: '.[4,2]'
input: '["a","b","c","d","e"]'
output: ['"e"', '"c"']
- title: "`|`"
body: |
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.
examples:
- program: '.[] | .name'
input: '[{"name":"JSON", "good":true}, {"name":"XML", "good":false}]'
output: ['"JSON"', '"XML"']
- title: Types and Values
body: |
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.
entries:
- title: Array construction - `[]`
body: |
As in JSON, `[]` is used to construct arrays, as in
`[1,2,3]`. The elements of the arrays can be any jq
expression. All of the results produced by all of the
expressions are collected into one big array. You can use it
to construct an array out of a known quantity of values (as
in `[.foo, .bar, .baz]`) or to "collect" all the results of a
filter into an array (as in `[.items[].name]`)
Once you understand the "," operator, you can look at jq's array
syntax in a different light: the expression `[1,2,3]` is not using a
built-in syntax for comma-separated arrays, but is instead applying
the `[]` operator (collect results) to the expression 1,2,3 (which
produces three different results).
If you have a filter `X` that produces four results,
then the expression `[X]` will produce a single result, an
array of four elements.
examples:
- program: "[.user, .projects[]]"
input: '{"user":"stedolan", "projects": ["jq", "wikiflow"]}'
output: ['["stedolan", "jq", "wikiflow"]']
- title: Objects - `{}`
body: |
Like JSON, `{}` is for constructing objects (aka
dictionaries or hashes), as in: `{"a": 42, "b": 17}`.
If the keys are "sensible" (all alphabetic characters), then
the quotes can be left off. The value can be any expression
(although you may need to wrap it in parentheses if it's a
complicated one), which gets applied to the {} expression's
input (remember, all filters have an input and an
output).
{foo: .bar}
will produce the JSON object `{"foo": 42}` if given the JSON
object `{"bar":42, "baz":43}`. You can use this to select
particular fields of an object: if the input is an object
with "user", "title", "id", and "content" fields and you
just want "user" and "title", you can write
{user: .user, title: .title}
Because that's so common, there's a shortcut syntax: `{user, title}`.
If one of the expressions produces multiple results,
multiple dictionaries will be produced. If the input's
{"user":"stedolan","titles":["JQ Primer", "More JQ"]}
then the expression
{user, title: .titles[]}
will produce two outputs:
{"user":"stedolan", "title": "JQ Primer"}
{"user":"stedolan", "title": "More JQ"}
Putting parentheses around the key means it will be evaluated as an
expression. With the same input as above,
{(.user): .titles}
produces
{"stedolan": ["JQ Primer", "More JQ"]}
examples:
- program: '{user, title: .titles[]}'
input: '{"user":"stedolan","titles":["JQ Primer", "More JQ"]}'
output:
- '{"user":"stedolan", "title": "JQ Primer"}'
- '{"user":"stedolan", "title": "More JQ"}'
- program: '{(.user): .titles}'
input: '{"user":"stedolan","titles":["JQ Primer", "More JQ"]}'
output: ['{"stedolan": ["JQ Primer", "More JQ"]}']
- title: Builtin operators and functions
body: |
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.
entries:
- title: Addition - `+`
body: |
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.
examples:
- program: '.a + 1'
input: '{"a": 7}'
output: ['8']
- program: '.a + .b'
input: '{"a": [1,2], "b": [3,4]}'
output: ['[1,2,3,4]']
- program: '.a + null'
input: '{"a": 1}'
output: ['1']
- program: '.a + 1'
input: '{}'
output: ['1']
- program: '{a: 1} + {b: 2} + {c: 3} + {a: 42}'
input: 'null'
output: ['{"a": 42, "b": 2, "c": 3}']
- title: Subtraction - `-`
body: |
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.
examples:
- program: '4 - .a'
input: '{"a":3}'
output: ['1']
- program: . - ["xml", "yaml"]
input: '["xml", "yaml", "json"]'
output: ['["json"]']
- title: Multiplication, division, modulo - `*`, `/`, and `%`
body: |
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.
examples:
- program: '10 / . * 3'
input: 5
output: [6]
- program: '. / ", "'
input: '"a, b,c,d, e"'
output: ['["a","b,c,d","e"]']
- program: '{"k": {"a": 1, "b": 2}} * {"k": {"a": 0,"c": 3}}'
input: 'null'
output: ['{"k": {"a": 0, "b": 2, "c": 3}}']
- program: '.[] | (1 / .)?'
input: '[1,0,-1]'
output: ['1', '-1']
- title: "`length`"
body: |
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.
examples:
- program: '.[] | length'
input: '[[1,2], "string", {"a":2}, null]'
output: [2, 6, 1, 0]
- title: "`keys`, `keys_unsorted`"
body: |
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.
examples:
- program: 'keys'
input: '{"abc": 1, "abcd": 2, "Foo": 3}'
output: ['["Foo", "abc", "abcd"]']
- program: 'keys'
input: '[42,3,35]'
output: ['[0,1,2]']
- title: "`has(key)`"
body: |
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.
examples:
- program: 'map(has("foo"))'
input: '[{"foo": 42}, {}]'
output: ['[true, false]']
- program: 'map(has(2))'
input: '[[0,1], ["a","b","c"]]'
output: ['[false, true]']
- title: "`in`"
body: |
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`.
examples:
- program: '.[] | in({"foo": 42})'
input: '["foo", "bar"]'
output: ['true', 'false']
- program: 'map(in([0,1]))'
input: '[2, 0]'
output: ['[false, true]']
- title: "`path(path_expression)`"
body: |
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.
examples:
- program: 'path(.a[0].b)'
input: 'null'
output: ['["a",0,"b"]']
- program: '[path(..)]'
input: '{"a":[{"b":1}]}'
output: ['[[],["a"],["a",0],["a",0,"b"]]']
- title: "`del(path_expression)`"
body: |
The builtin function `del` removes a key and its corresponding
value from an object.
examples:
- program: 'del(.foo)'
input: '{"foo": 42, "bar": 9001, "baz": 42}'
output: ['{"bar": 9001, "baz": 42}']
- program: 'del(.[1, 2])'
input: '["foo", "bar", "baz"]'
output: ['["foo"]']
- title: "`to_entries`, `from_entries`, `with_entries`"
body: |
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, value and Value as keys.
examples:
- program: 'to_entries'
input: '{"a": 1, "b": 2}'
output: ['[{"key":"a", "value":1}, {"key":"b", "value":2}]']
- program: 'from_entries'
input: '[{"key":"a", "value":1}, {"key":"b", "value":2}]'
output: ['{"a": 1, "b": 2}']
- program: 'with_entries(.key |= "KEY_" + .)'
input: '{"a": 1, "b": 2}'
output: ['{"KEY_a": 1, "KEY_b": 2}']
- title: "`select(boolean_expression)`"
body: |
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]`.
examples:
- program: 'map(select(. >= 2))'
input: '[1,5,3,0,7]'
output: ['[5,3,7]']
- program: '.[] | select(.id == "second")'
input: '[{"id": "first", "val": 1}, {"id": "second", "val": 2}]'
output: ['{"id": "second", "val": 2}']
- title: "`arrays`, `objects`, `iterables`, `booleans`, `numbers`, `normals`, `finites`, `strings`, `nulls`, `values`, `scalars`"
body: |
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.
examples:
- program: '.[]|numbers'
input: '[[],{},1,"foo",null,true,false]'
output: ['1']
- title: "`empty`"
body: |
`empty` returns no results. None at all. Not even `null`.
It's useful on occasion. You'll know if you need it :)
examples:
- program: '1, empty, 2'
input: 'null'
output: [1, 2]
- program: '[1,2,empty,3]'
input: 'null'
output: ['[1,2,3]']
- title: "`error(message)`"
body: |
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.
- title: "`$__loc__`"
body: |
Produces an object with a "file" key and a "line" key, with
the filename and line number where `$__loc__` occurs, as
values.
examples:
- program: 'try error("\($__loc__)") catch .'
input: 'null'
output: ['"{\"file\":\"<top-level>\",\"line\":1}"']
- title: "`map(x)`, `map_values(x)`"
body: |
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`.
examples:
- program: 'map(.+1)'
input: '[1,2,3]'
output: ['[2,3,4]']
- program: 'map_values(.+1)'
input: '{"a": 1, "b": 2, "c": 3}'
output: ['{"a": 2, "b": 3, "c": 4}']
- title: "`paths`, `paths(node_filter)`, `leaf_paths`"
body: |
`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.
examples:
- program: '[paths]'
input: '[1,[[],{"a":2}]]'
output: ['[[0],[1],[1,0],[1,1],[1,1,"a"]]']
- program: '[paths(scalars)]'
input: '[1,[[],{"a":2}]]'
output: ['[[0],[1,1,"a"]]']
- title: "`add`"
body: |
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`.
examples:
- program: add
input: '["a","b","c"]'
output: ['"abc"']
- program: add
input: '[1, 2, 3]'
output: [6]
- program: add
input: '[]'
output: ["null"]
- title: "`any`, `any(condition)`, `any(generator; condition)`"
body: |
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.
examples:
- program: any
input: '[true, false]'
output: ["true"]
- program: any
input: '[false, false]'
output: ["false"]
- program: any
input: '[]'
output: ["false"]
- title: "`all`, `all(condition)`, `all(generator; condition)`"
body: |
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`.
examples:
- program: all
input: '[true, false]'
output: ["false"]
- program: all
input: '[true, true]'
output: ["true"]
- program: all
input: '[]'
output: ["true"]
- title: "`flatten`, `flatten(depth)`"
body: |
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.
examples:
- program: flatten
input: '[1, [2], [[3]]]'
output: ["[1, 2, 3]"]
- program: flatten(1)
input: '[1, [2], [[3]]]'
output: ["[1, 2, [3]]"]
- program: flatten
input: '[[]]'
output: ["[]"]
- program: flatten
input: '[{"foo": "bar"}, [{"foo": "baz"}]]'
output: ['[{"foo": "bar"}, {"foo": "baz"}]']
- title: "`range(upto)`, `range(from;upto)` `range(from;upto;by)`"
body: |
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`.
examples:
- program: 'range(2;4)'
input: 'null'
output: ['2', '3']
- program: '[range(2;4)]'
input: 'null'
output: ['[2,3]']
- program: '[range(4)]'
input: 'null'
output: ['[0,1,2,3]']
- program: '[range(0;10;3)]'
input: 'null'
output: ['[0,3,6,9]']
- program: '[range(0;10;-1)]'
input: 'null'
output: ['[]']
- program: '[range(0;-5;-1)]'
input: 'null'
output: ['[0,-1,-2,-3,-4]']
- title: "`floor`"
body: |
The `floor` function returns the floor of its numeric input.
examples:
- program: 'floor'
input: '3.14159'
output: ['3']
- title: "`sqrt`"
body: |
The `sqrt` function returns the square root of its numeric input.
examples:
- program: 'sqrt'
input: '9'
output: ['3']
- title: "`tonumber`"
body: |
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.
examples:
- program: '.[] | tonumber'
input: '[1, "1"]'
output: [1, 1]
- title: "`tostring`"
body: |
The `tostring` function prints its input as a
string. Strings are left unchanged, and all other values are
JSON-encoded.
examples:
- program: '.[] | tostring'
input: '[1, "1", [1]]'
output: ['"1"', '"1"', '"[1]"']
- title: "`type`"
body: |
The `type` function returns the type of its argument as a
string, which is one of null, boolean, number, string, array
or object.
examples:
- program: 'map(type)'
input: '[0, false, [], {}, null, "hello"]'
output: ['["number", "boolean", "array", "object", "null", "string"]']
- title: "`infinite`, `nan`, `isinfinite`, `isnan`, `isfinite`, `isnormal`"
body: |
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.
examples:
- program: '.[] | (infinite * .) < 0'
input: '[-1, 1]'
output: ['true', 'false']
- program: 'infinite, nan | type'
input: 'null'
output: ['"number"', '"number"']
- title: "`sort, sort_by(path_expression)`"
body: |
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.
examples:
- program: 'sort'
input: '[8,3,null,6]'
output: ['[null,3,6,8]']
- program: 'sort_by(.foo)'
input: '[{"foo":4, "bar":10}, {"foo":3, "bar":100}, {"foo":2, "bar":1}]'
output: ['[{"foo":2, "bar":1}, {"foo":3, "bar":100}, {"foo":4, "bar":10}]']
- title: "`group_by(path_expression)`"
body: |
`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.
examples:
- program: 'group_by(.foo)'
input: '[{"foo":1, "bar":10}, {"foo":3, "bar":100}, {"foo":1, "bar":1}]'
output: ['[[{"foo":1, "bar":10}, {"foo":1, "bar":1}], [{"foo":3, "bar":100}]]']
- title: "`min`, `max`, `min_by(path_exp)`, `max_by(path_exp)`"
body: |
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.
examples:
- program: 'min'
input: '[5,4,2,7]'
output: ['2']
- program: 'max_by(.foo)'
input: '[{"foo":1, "bar":14}, {"foo":2, "bar":3}]'
output: ['{"foo":2, "bar":3}']
- title: "`unique`, `unique_by(path_exp)`"
body: |
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`.
examples:
- program: 'unique'
input: '[1,2,5,3,5,3,1,3]'
output: ['[1,2,3,5]']
- program: 'unique_by(.foo)'
input: '[{"foo": 1, "bar": 2}, {"foo": 1, "bar": 3}, {"foo": 4, "bar": 5}]'
output: ['[{"foo": 1, "bar": 2}, {"foo": 4, "bar": 5}]']
- program: 'unique_by(length)'
input: '["chunky", "bacon", "kitten", "cicada", "asparagus"]'
output: ['["bacon", "chunky", "asparagus"]']
- title: "`reverse`"
body: |
This function reverses an array.
examples:
- program: 'reverse'
input: '[1,2,3,4]'
output: ['[4,3,2,1]']
- title: "`contains(element)`"
body: |
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.
examples:
- program: 'contains("bar")'
input: '"foobar"'
output: ['true']
- program: 'contains(["baz", "bar"])'
input: '["foobar", "foobaz", "blarp"]'
output: ['true']
- program: 'contains(["bazzzzz", "bar"])'
input: '["foobar", "foobaz", "blarp"]'
output: ['false']
- program: 'contains({foo: 12, bar: [{barp: 12}]})'
input: '{"foo": 12, "bar":[1,2,{"barp":12, "blip":13}]}'
output: ['true']
- program: 'contains({foo: 12, bar: [{barp: 15}]})'
input: '{"foo": 12, "bar":[1,2,{"barp":12, "blip":13}]}'
output: ['false']
- title: "`indices(s)`"
body: |
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`.
examples:
- program: 'indices(", ")'
input: '"a,b, cd, efg, hijk"'
output: ['[3,7,12]']
- program: 'indices(1)'
input: '[0,1,2,1,3,1,4]'
output: ['[1,3,5]']
- program: 'indices([1,2])'
input: '[0,1,2,3,1,4,2,5,1,2,6,7]'
output: ['[1,8]']
- title: "`index(s)`, `rindex(s)`"
body: |
Outputs the index of the first (`index`) or last (`rindex`)
occurrence of `s` in the input.
examples:
- program: 'index(", ")'
input: '"a,b, cd, efg, hijk"'
output: ['3']
- program: 'rindex(", ")'
input: '"a,b, cd, efg, hijk"'
output: ['12']
- title: "`inside`"
body: |
The filter `inside(b)` will produce true if the input is
completely contained within b. It is, essentially, an
inversed version of `contains`.
examples:
- program: 'inside("foobar")'
input: '"bar"'
output: ['true']
- program: 'inside(["foobar", "foobaz", "blarp"])'
input: '["baz", "bar"]'
output: ['true']
- program: 'inside(["foobar", "foobaz", "blarp"])'
input: '["bazzzzz", "bar"]'
output: ['false']
- program: 'inside({"foo": 12, "bar":[1,2,{"barp":12, "blip":13}]})'
input: '{"foo": 12, "bar": [{"barp": 12}]}'
output: ['true']
- program: 'inside({"foo": 12, "bar":[1,2,{"barp":12, "blip":13}]})'
input: '{"foo": 12, "bar": [{"barp": 15}]}'
output: ['false']
- title: "`startswith(str)`"
body: |
Outputs `true` if . starts with the given string argument.
examples:
- program: '[.[]|startswith("foo")]'
input: '["fo", "foo", "barfoo", "foobar", "barfoob"]'
output: ['[false, true, false, true, false]']
- title: "`endswith(str)`"
body: |
Outputs `true` if . ends with the given string argument.
examples:
- program: '[.[]|endswith("foo")]'
input: '["foobar", "barfoo"]'
output: ['[false, true]']
- title: "`combinations`, `combinations(n)`"
body: |
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.
examples:
- program: 'combinations'
input: '[[1,2], [3, 4]]'
output: ['[1, 3]', '[1, 4]', '[2, 3]', '[2, 4]']
- program: 'combinations(2)'
input: '[0, 1]'
output: ['[0, 0]', '[0, 1]', '[1, 0]', '[1, 1]']
- title: "`ltrimstr(str)`"
body: |
Outputs its input with the given prefix string removed, if it
starts with it.
examples:
- program: '[.[]|ltrimstr("foo")]'
input: '["fo", "foo", "barfoo", "foobar", "afoo"]'
output: ['["fo","","barfoo","bar","afoo"]']
- title: "`rtrimstr(str)`"
body: |
Outputs its input with the given suffix string removed, if it
ends with it.
examples:
- program: '[.[]|rtrimstr("foo")]'
input: '["fo", "foo", "barfoo", "foobar", "foob"]'
output: ['["fo","","bar","foobar","foob"]']
- title: "`explode`"
body: |
Converts an input string into an array of the string's
codepoint numbers.
examples:
- program: 'explode'
input: '"foobar"'
output: ['[102,111,111,98,97,114]']
- title: "`implode`"
body: |
The inverse of explode.
examples:
- program: 'implode'
input: '[65, 66, 67]'
output: ['"ABC"']
- title: "`split`"
body: |
Splits an input string on the separator argument.
examples:
- program: 'split(", ")'
input: '"a, b,c,d, e, "'
output: ['["a","b,c,d","e",""]']
- title: "`join(str)`"
body: |
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.
examples:
- program: 'join(", ")'
input: '["a","b,c,d","e"]'
output: ['"a, b,c,d, e"']
- title: "`ascii_downcase`, `ascii_upcase`"
body: |
Emit a copy of the input string with its alphabetic characters (a-z and A-Z)
converted to the specified case.
example:
- program: 'ascii_upcase'
input: '"useful but not for é"'
output: '"USEFUL BUT NOT FOR é"'
- title: "`while(cond; update)`"
body: |
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.
examples:
- program: '[while(.<100; .*2)]'
input: '1'
output: ['[1,2,4,8,16,32,64]']
- title: "`until(cond; next)`"
body: |
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.
examples:
- program: '[.,1]|until(.[0] < 1; [.[0] - 1, .[1] * .[0]])|.[1]'
input: '4'
output: ['24']
- title: "`recurse(f)`, `recurse`, `recurse(f; condition)`, `recurse_down`"
body: |
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.
examples:
- program: 'recurse(.foo[])'
input: '{"foo":[{"foo": []}, {"foo":[{"foo":[]}]}]}'
output:
- '{"foo":[{"foo":[]},{"foo":[{"foo":[]}]}]}'
- '{"foo":[]}'
- '{"foo":[{"foo":[]}]}'
- '{"foo":[]}'
- program: 'recurse'
input: '{"a":0,"b":[1]}'
output:
- '{"a":0,"b":[1]}'
- '0'
- '[1]'
- '1'
- program: 'recurse(. * .; . < 20)'
input: 2
output:
- 2
- 4
- 16
- title: "`..`"
body: |
Short-hand for `recurse` without arguments. 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" `.`.
examples:
- program: '..|.a?'
input: '[[{"a":1}]]'
output: ['1']
- title: "`env`"
body: |
Outputs an object representing jq's environment.
examples:
- program: 'env.PAGER'
input: 'null'
output: ['"less"']
- title: "`transpose`"
body: |
Transpose a possibly jagged matrix (an array of arrays).
Rows are padded with nulls so the result is always rectangular.
examples:
- program: 'transpose'
input: '[[1], [2,3]]'
output: ['[[1,2],[null,3]]']
- title: "`bsearch(x)`"
body: |
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.
examples:
- program: 'bsearch(0)'
input: '[0,1]'
output: ['0']
- program: 'bsearch(0)'
input: '[1,2,3]'
output: ['-1']
- program: 'bsearch(4) as $ix | if $ix < 0 then .[-(1+$ix)] = 4 else . end'
input: '[1,2,3]'
output: ['[1,2,3,4]']
- title: "String interpolation - `\\(foo)`"
body: |
Inside a string, you can put an expression inside parens
after a backslash. Whatever the expression returns will be
interpolated into the string.
examples:
- program: '"The input was \(.), which is one less than \(.+1)"'
input: '42'
output: ['"The input was 42, which is one less than 43"']
- title: "Convert to/from JSON"
body: |
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.
examples:
- program: '[.[]|tostring]'
input: '[1, "foo", ["foo"]]'
output: ['["1","foo","[\"foo\"]"]']
- program: '[.[]|tojson]'
input: '[1, "foo", ["foo"]]'
output: ['["1","\"foo\"","[\"foo\"]"]']
- program: '[.[]|tojson|fromjson]'
input: '[1, "foo", ["foo"]]'
output: ['[1,"foo",["foo"]]']
- title: "Format strings and escaping"
body: |
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 `&lt;`, `&gt;`,
`&amp;`, `&apos;`, `&quot;`.
* `@uri`:
Applies percent-encoding, by mapping all reserved URI
characters to a `%XX` sequence.
* `@csv`:
The input must be an array, and it is rendered as CSV
with double quotes for strings, and quotes escaped by
repetition.
* `@tsv`:
The input must be an array, and it is rendered as TSV
(tab-separated 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.
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.
examples:
- program: '@html'
input: '"This works if x < y"'
output: ['"This works if x &lt; y"']
# - program: '@html "<span>Anonymous said: \(.)</span>"'
# input: '"<script>alert(\"lol hax\");</script>"'
# output: ["<span>Anonymous said: &lt;script&gt;alert(&quot;lol hax&quot;);&lt;/script&gt;</span>"]
- program: '@sh "echo \(.)"'
input: "\"O'Hara's Ale\""
output: ["\"echo 'O'\\\\''Hara'\\\\''s Ale'\""]
- title: "Dates"
body: |
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`, `mktime`, and `gmtime`.
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
time as an array of numbers representing (in this order): the
year, the month (zero-based), the day of the month, 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 `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 with the given
format.
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.
examples:
- program: 'fromdate'
input: '"2015-03-05T23:51:47Z"'
output: ['1425599507']
- program: 'strptime("%Y-%m-%dT%H:%M:%SZ")'
input: '"2015-03-05T23:51:47Z"'
output: ['[2015,2,5,23,51,47,4,63]']
- program: 'strptime("%Y-%m-%dT%H:%M:%SZ")|mktime'
input: '"2015-03-05T23:51:47Z"'
output: ['1425599507']
- title: Conditionals and Comparisons
entries:
- title: "`==`, `!=`"
body: |
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'
examples:
- program: '.[] == 1'
input: '[1, 1.0, "1", "banana"]'
output: ['true', 'true', 'false', 'false']
- title: if-then-else
body: |
`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.
examples:
- program: |-
if . == 0 then
"zero"
elif . == 1 then
"one"
else
"many"
end
input: 2
output: ['"many"']
- title: "`>, >=, <=, <`"
body: |
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.
examples:
- program: '. < 5'
input: 2
output: ['true']
- title: and/or/not
body: |
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.
examples:
- program: '42 and "a string"'
input: 'null'
output: ['true']
- program: '(true, false) or false'
input: 'null'
output: ['true', 'false']
# - program: '(true, false) and (true, false)'
# input: 'null'
# output: ['true', 'false', 'false', 'false']
- program: '(true, true) and (true, false)'
input: 'null'
output: ['true', 'false', 'true', 'false']
- program: '[true, false | not]'
input: 'null'
output: ['[false, true]']
- title: Alternative operator - `//`
body: |
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).
examples:
- program: '.foo // 42'
input: '{"foo": 19}'
output: [19]
- program: '.foo // 42'
input: '{}'
output: [42]
- title: try-catch
body: |
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.
examples:
- program: 'try .a catch ". is not an object"'
input: 'true'
output: ['". is not an object"']
- program: '[.[]|try .a]'
input: '[{}, true, {"a":1}]'
output: ['[null, 1]']
- program: 'try error("some exception") catch .'
input: 'true'
output: ['"some exception"']
- title: Breaking out of control structures
body: |
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.
- title: "`?` operator"
body: |
The `?` operator, used as `EXP?`, is shorthand for `try EXP`.
examples:
- program: '[.[]|(.a)?]'
input: '[{}, true, {"a":1}]'
output: ['[null, 1]']
- title: Regular expressions (PCRE)
body: |
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.
entries:
- title: "`test(val)`, `test(regex; flags)`"
body: |
Like `match`, but does not return match objects, only `true` or `false`
for whether or not the regex matches the input.
examples:
- program: 'test("foo")'
input: '"foo"'
output: ['true']
- program: '.[] | test("a b c # spaces are ignored"; "ix")'
input: '["xabcd", "ABC"]'
output: ['true', 'true']
- title: "`match(val)`, `match(regex; flags)`"
body: |
**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
examples:
- program: 'match("(abc)+"; "g")'
input: '"abc abc"'
output:
- '{"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}]}'
- program: 'match("foo")'
input: '"foo bar foo"'
output: ['{"offset": 0, "length": 3, "string": "foo", "captures": []}']
- program: 'match(["foo", "ig"])'
input: '"foo bar FOO"'
output:
- '{"offset": 0, "length": 3, "string": "foo", "captures": []}'
- '{"offset": 8, "length": 3, "string": "FOO", "captures": []}'
- program: 'match("foo (?<bar123>bar)? foo"; "ig")'
input: '"foo bar foo foo foo"'
output:
- '{"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"}]}'
- program: '[ match("."; "g")] | length'
input: '"abc"'
output: [3]
- title: "`capture(val)`, `capture(regex; flags)`"
body: |
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.
examples:
- program: 'capture("(?<a>[a-z]+)-(?<n>[0-9]+)")'
input: '"xyzzy-14"'
output: ['{ "a": "xyzzy", "n": "14" }']
- title: "`scan(regex)`, `scan(regex; flags)`"
body: |
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) ]`.
example:
- program: 'scan("c")'
input: '"abcdefabc"'
output: ['"c"', '"c"']
- program: 'scan("b")'
input: ("", "")
output: ['[]', '[]']
- title: "`split(regex; flags)`"
body: |
For backwards compatibility, `split` splits on a string, not a regex.
example:
- program: 'split(", *"; null)'
input: '"ab,cd, ef"'
output: ['"ab","cd","ef"']
- title: "`splits(regex)`, `splits(regex; flags)`"
body: |
These provide the same results as their `split` counterparts,
but as a stream instead of an array.
example:
- program: 'splits(", *")'
input: '("ab,cd", "ef, gh")'
output: ['"ab"', '"cd"', '"ef"', '"gh"']
- title: "`sub(regex; tostring)` `sub(regex; string; flags)`"
body: |
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)".
example:
- program: 'sub("^[^a-z]*(?<x>[a-z]*).*")'
input: '"123abc456"'
output: '"ZabcZabc"'
- title: "`gsub(regex; string)`, `gsub(regex; string; flags)`"
body: |
`gsub` is like `sub` but all the non-overlapping occurrences of the regex are
replaced by the string, after interpolation.
example:
- program: 'gsub("(?<x>.)[^a]*"; "+\(.x)-")'
input: '"Abcabc"'
output: '"+A-+a-"'
- title: Advanced features
body: |
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.
entries:
- title: Variables
body: |
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.
examples:
- program: '.bar as $x | .foo | . + $x'
input: '{"foo":10, "bar":200}'
output: ['210']
- program: '. as $i|[(.*2|. as $i| $i), $i]'
input: '5'
output: ['[10,5]']
- program: '. as [$a, $b, {c: $c}] | $a + $b + $c'
input: '[2, 3, {"c": 4, "d": 5}]'
output: ['9']
- program: '.[] as [$a, $b] | {a: $a, b: $b}'
input: '[[0], [0, 1], [2, 1, 0]]'
output: ['{"a":0,"b":null}', '{"a":0,"b":1}', '{"a":2,"b":1}']
- title: 'Defining Functions'
body: |
You can give a filter a name using "def" syntax:
def increment: . + 1;
From then on, `increment` is usable as a filter just like a
builtin function (in fact, this is how some of the builtins
are defined). A function may take arguments:
def map(f): [.[] | f];
Arguments are passed as filters, not as values. The
same argument may be referenced multiple times with
different inputs (here `f` is run for each element of the
input array). Arguments to a function work more like
callbacks than like value arguments. 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.
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.
examples:
- program: 'def addvalue(f): . + [f]; map(addvalue(.[0]))'
input: '[[1,2],[10,20]]'
output: ['[[1,2,1], [10,20,10]]']
- program: 'def addvalue(f): f as $x | map(. + $x); addvalue(.[0])'
input: '[[1,2],[10,20]]'
output: ['[[1,2,1,2], [10,20,1,2]]']
- title: Reduce
body: |
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)
examples:
- program: 'reduce .[] as $item (0; . + $item)'
input: '[10,2,5,3]'
output: ['20']
- title: "`limit(n; exp)`"
body: |
The `limit` function extracts up to `n` outputs from `exp`.
examples:
- program: '[limit(3;.[])]'
input: '[0,1,2,3,4,5,6,7,8,9]'
output: ['[0,1,2]']
- title: "`first(expr)`, `last(expr)`, `nth(n; expr)`"
body: |
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`.
examples:
- program: '[first(range(.)), last(range(.)), nth(./2; range(.))]'
input: '10'
output: ['[0,9,5]']
- title: "`first`, `last`, `nth(n)`"
body: |
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 `.`.
examples:
- program: '[range(.)]|[first, last, nth(5)]'
input: '10'
output: ['[0,9,5]']
- title: "`foreach`"
body: |
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).
examples:
- program: '[foreach .[] as $item
([[],[]];
if $item == null then [[],.[0]] else [(.[0] + [$item]),[]] end;
if $item == null then .[1] else empty end)]'
input: '[1,2,3,4,null,"a","b",null]'
output: ['[[1,2,3,4],["a","b"]]']
- title: Recursion
body: |
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;
- title: Generators and iterators
body: |
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.
examples:
- program: '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)'
input: 'null'
output: ['0', '3', '6', '9']
- program: 'def while(cond; update):
def _while:
if cond then ., (update | _while) else empty end;
_while;
[while(.<100; .*2)]'
input: '1'
output: ['[1,2,4,8,16,32,64]']
- title: 'Math'
body: |
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 `.`.
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.
- title: 'I/O'
body: |
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.
One builtin provides minimal output capabilities, `debug`.
(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.
entries:
- title: "`input`"
body: |
Outputs one new input.
- title: "`inputs`"
body: |
Outputs all remaining inputs, one by one.
This is primarily useful for reductions over a program's
inputs.
- title: "`debug`"
body: |
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.
- title: "`input_filename`"
body: |
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.
- title: "`input_line_number`"
body: |
Returns the line number of the input currently being filtered.
- title: 'Streaming'
body: |
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.
entries:
- title: "`truncate_stream(stream_expression)`"
body: |
Consumes a number as input and truncates the corresponding
number of path elements from the left of the outputs of the
given streaming expression.
examples:
- program: '[1|truncate_stream([[0],1],[[1,0],2],[[1,0]],[[1]])]'
input: '1'
output: ['[[[0],2],[[0]]]']
- title: "`fromstream(stream_expression)`"
body: |
Outputs values corresponding to the stream expression's
outputs.
examples:
- program: 'fromstream(1|truncate_stream([[0],1],[[1,0],2],[[1,0]],[[1]]))'
input: 'null'
output: ['[2]']
- title: "`tostream`"
body: |
The `tostream` builtin outputs the streamed form of its input.
examples:
- program: '. as $dot|fromstream($dot|tostream)|.==$dot'
input: '[0,[1,{"a":1},{"b":2}]]'
output: ['true']
- title: Assignment
body: |
Assignment works a little differently in jq than in most
programming languages. jq doesn't distinguish between references
to and copies of something - two objects or arrays are either
equal or not equal, without any further notion of being "the
same object" or "not the same object".
If an object has two fields which are arrays, `.foo` and `.bar`,
and you append something to `.foo`, then `.bar` will not get
bigger. Even if you've just set `.bar = .foo`. If you're used to
programming in languages like Python, Java, Ruby, Javascript,
etc. then you can think of it as though jq does a full deep copy
of every object before it does the assignment (for performance,
it doesn't actually do that, but that's the general idea).
All the assignment operators in jq have path expressions on the
left-hand side.
entries:
- title: "`=`"
body: |
The filter `.foo = 1` will take as input an object
and produce as output an object with the "foo" field set to
1. There is no notion of "modifying" or "changing" something
in jq - all jq values are immutable. For instance,
.foo = .bar | .foo.baz = 1
will not have the side-effect of setting .bar.baz to be set
to 1, as the similar-looking program in Javascript, Python,
Ruby or other languages would. Unlike these languages (but
like Haskell and some other functional languages), there is
no notion of two arrays or objects being "the same array" or
"the same object". They can be equal, or not equal, but if
we change one of them in no circumstances will the other
change behind our backs.
This means that it's impossible to build circular values in
jq (such as an array whose first element is itself). This is
quite intentional, and ensures that anything a jq program
can produce can be represented in JSON.
Note that the left-hand side of '=' refers to a value in `.`.
Thus `$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 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 below) do
not do this.
Note too that `.a,.b=0` does not set `.a` and `.b`, but
`(.a,.b)=0` sets both.
- title: "`|=`"
body: |
As well as the assignment operator '=', jq provides the "update"
operator '|=', which takes a filter on the right-hand side and
works out the new value for the property of `.` being assigned
to by running the old value through this expression. For
instance, .foo |= .+1 will build an object with the "foo"
field set to the input's "foo" plus 1.
This example should show the difference between '=' and '|=':
Provide input '{"a": {"b": 10}, "b": 20}' to the programs:
.a = .b
.a |= .b
The former will set the "a" field of the input to the "b" field of the
input, and produce the output {"a": 20}. The latter will set the "a"
field of the input to the "a" field's "b" field, producing {"a": 10}.
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 multiple values, only the last
one will be used.
examples:
- program: '(..|select(type=="boolean")) |= if . then 1 else 0 end'
input: '[true,false,[5,true,[true,[false]],false]]'
output: ['[1,0,[5,1,[1,[0]],0]]']
- title: "`+=`, `-=`, `*=`, `/=`, `%=`, `//=`"
body: |
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.
examples:
- program: .foo += 1
input: '{"foo": 42}'
output: ['{"foo": 43}']
- title: Complex assignments
body: |
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."]
- title: Modules
body: |
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.
entries:
- title: "`import RelativePathString as NAME [<metadata>];`"
body: |
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.
- title: "`include RelativePathString [<metadata>];`"
body: |
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.
- title: "`import RelativePathString as $NAME [<metadata>];`"
body: |
Imports a JSON file found at the given path relative to a
directory in a search path. A ".json" suffix will be added to
the relative path string. The file's data will be available
as `$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.
- title: "`module <metadata>;`"
body: |
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.
- title: "`modulemeta`"
body: |
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.