The data templating language
Jsonnet

Standard Library

This page describes the functions available in Jsonnet's standard library, i.e. the object implicitly bound to the std variable. Some of the standard library functions can be implemented in Jsonnet. Their code can be found in the std.jsonnet file. The behavior of some of the other functions, i.e. the ones that expose extra functionality not otherwise available to programmers, is described formally in the specification.

The standard library is implicitly added to all Jsonnet programs by enclosing them in a local construct. For example, if the program given by the user is {x: "foo"}, then the actual code executed would be local std = { ... }; {x: "foo"}. The functions in the standard library are all hidden fields of the std object.

External Variables

std.extVar(x)

If an external variable with the given name was defined, return its string value. Otherwise, raise an error.

Types and Reflection

std.thisFile

Note that this is a field. It contains the current Jsonnet filename as a string.

std.type(x)

Return a string that indicates the type of the value. The possible return values are: "array", "boolean", "function", "null", "number", "object", and "string".

std.length(x)

Depending on the type of the value given, either returns the number of elements in the array, the number of codepoints in the string, the number of parameters in the function, or the number of fields in the object. Raises an error if given a primitive value, i.e. null, true or false.

std.objectHas(o, f)

Returns true if the given object has the field (given as a string), otherwise false. Raises an error if the arguments are not object and string respectively. Returns false if the field is hidden..

std.objectFields(o)

Returns an array of strings, each element being a field from the given object. Does not include hidden fields.

std.objectHasAll(o, f)

As std.objectHas but also includes hidden fields.

std.objectFieldsAll(o)

As std.objectFields but also includes hidden fields.

std.prune(x)

Recursively remove all "empty" members of `x`. "Empty" is defined as zero length `arrays`, zero length `objects`, or `null` values.

Mathematical Utilities

The following mathematical functions are available: std.abs(n), std.max(a, b), std.min(a, b), std.pow(x, n), std.exp(x), std.exponent(x), std.mantissa(x), std.floor(x), std.ceil(x), std.sqrt(x), std.sin(x), std.cos(x), std.tan(x), std.asin(x), std.acos(x), and std.atan(x).

The function std.mod(a, b) is what the % operator is desugared to. It performs modulo arithmetic if the left hand side is a number, or if the left hand side is a string, it does Python-style string formatting with std.format().

Assertions and Debugging

std.assertEqual(a, b)

Ensure that a == b. Returns true or throws an error message.

String Manipulation

std.toString(a)

Convert the given argument to a string.

std.codepoint(str)

Returns the positive integer representing the unicode codepoint of the character in the given single-character string. This function is the inverse of std.char(n).

std.char(n)

Returns a string of length one whose only unicode codepoint has integer id n. This function is the inverse of std.codepoint(str).

std.substr(s, from, len)

Returns a string that is the part of s that starts at offset from and is len codepoints long.

std.startsWith(a, b)

Returns whether the string a is prefixed by the string b.

std.endsWith(a, b)

Returns whether the string a is suffixed by the string b.

std.substr(s, from, len)

Returns a string that is the part of s that starts at offset from and is len codepoints long.

std.split(str, c)

Split the string str into an array of strings, divided by the single character c.

Example: std.split("foo/bar", "/") yields ["foo", "bar"].

Example: std.split("/foo/", "/") yields ["", "foo", ""].

std.splitLimit(str, c, maxsplits)

As std.split(str, c) but will stop after maxsplits splits, thereby the largest array it will return has length maxsplits + 1. A limit of -1 means unlimited.

Example: std.splitLimit("foo/bar", "/", 1) yields ["foo", "bar"].

Example: std.splitLimit("/foo/", "/", 1) yields ["", "foo/"].

std.stringChars(str)

Split the string str into an array of strings, each containing a single codepoint.

Example: std.stringChars("foo") yields ["f", "o", "o"].

std.format(str, vals)

Format the string str using the values in vals. The values can be an array, an object, or in other cases are treated as if they were provided in a singleton array. The string formatting follows the same rules as Python. The % operator can be used as a shorthand for this function.

Example: std.format("Hello %03d", 12) yields "Hello 012".

Example: "Hello %03d" % 12 yields "Hello 012".

Example: "Hello %s, age %d" % ["Foo", 25] yields "Hello Foo, age 25".

Example: "Hello %(name)s, age %(age)d" % {age: 25, name: "Foo"} yields "Hello Foo, age 25".

std.parseInt(str)

Parses a signed decimal integer from the input string

Example: std.parseInt("123") yields 123.

Example: std.parseInt("-123") yields -123.

std.escapeStringBash(str)

Wrap str in single quotes, and escape any single quotes within str by changing them to a sequence '"'"'. This allows injection of arbitrary strings as arguments of commands in bash scripts.

std.escapeStringDollars(str)

Convert $ to $$ in str. This allows injection of arbitrary strings into systems that use $ for string interpolation (like Terraform).

std.escapeStringJson(str)

Convert str to allow it to be embedded in a JSON representation, within a string. This adds quotes, escapes backslashes, and escapes unprintable characters.

Example:
{ local description = "Multiline\nc:\\path", json: "{name: %s}" % std.escapeStringJson(description) }
yields: {"json": "{name: \"Multiline\\nc:\\\\path\"}"}

std.escapeStringPython(str)

Convert str to allow it to be embedded in Python. This is an alias for std.escapeStringJson.

Manifestation

std.manifestIni(v)

Convert the given structure to a string in INI format. This allows using Jsonnet's object model to build a configuration to be consumed by an application expecting an INI file. The data is in the form of a set of sections, each containing a key/value mapping. These examples should make it clear:

{ main: { a: "1", b: "2" }, sections: { s1: {x: "11", y: "22", z: "33"}, s2: {p: "yes", q: ""}, empty: {}, } }

Yields a string containing this INI file:

a = 1 b = 2 [empty] [s1] x = 11 y = 22 z = 33 [s2] p = yes q =

std.manifestPython(v)

Convert the given value to a JSON-like form that is compatible with Python. The chief differences are True / False / None instead of true / false / null.

{ b: ["foo", "bar"], c: true, d: null, e: { f1: false, f2: 42 }, }

Yields a string containing this Python code:

{"b": ["foo", "bar"], "c": True, "d": None, "e": {"f1": False, "f2": 42}}

std.manifestPythonVars(v)

Convert the given object to a JSON-like form that is compatible with Python. The key difference to std.manifestPython is that the top level is represented as a list of Python global variables.

{ b: ["foo", "bar"], c: true, d: null, e: { f1: false, f2: 42 }, }

Yields a string containing this Python code:

b = ["foo", "bar"] c = True d = None e = {"f1": False, "f2": 42}

Arrays

std.makeArray(sz, func)

Create a new array of sz elements by calling func(i) to initialize each element. Func is expected to be a function that takes a single parameter, the index of the element it should initialize.

Example: std.makeArray(3,function(x) x * x) yields [0, 1, 4].

std.count(arr, x)

Return the number of times that x occurs in arr.

std.map(func, arr)

Apply the given function to every element of the array to form a new array.

std.filterMap(filter_func, map_func, arr)

This is primarily used to desugar array comprehension syntax. It first filters, then maps thte given array, using the two functions provided.

std.filter(func, arr)

Return a new array containing all the elements of arr for which the func function returns true.

std.foldl(func, arr, init)

Classic foldl function. Calls the function on the result of the previous function call and each array element, or init in the case of the initial element. Traverses the array from left to right.

std.foldr(func, arr, init)

Classic foldl function. Calls the function on each array element and the result of the previous function call, or init in the case of the initial element. Traverses the array from right to left.

std.range(from, to)

Return an array of ascending numbers between the two limits, inclusively.

std.join(sep, arr)

If sep is a string, then arr must be an array of strings, in which case they are concatenated with sep used as a delimiter. If sep is an array, then arr must be an array of arrays, in which case the arrays are concatenated in the same way, to produce a single array.

Example1: std.join(".", ["www", "google", "com"]) yields "www.google.com".

Example2: std.join([9, 9], [[1], [2, 3]]) yields [1, 9, 9, 2, 3].

std.lines(arr)

Concatenate an array of strings into a text file with newline characters after each string. This is suitable for constructing bash scripts and the like.

std.flattenArrays(arrs)

Concatenate an array of arrays into a single array.

std.sort(arr)

Sorts the array using the <= operator.

std.uniq(arr)

Removes successive duplicates. When given a sorted array, removes all duplicates.

Sets

Sets are represented as ordered arrays without duplicates.

std.set(arr)

Syntax sugar for std.uniq(std.sort(arr)).

std.setInter(a, b)

Set intersection operation (values in both a and b).

std.setUnion(a, b)

Set union operation (values in either a or b). Note that + on sets will simply concatenate the arrays, possibly forming an array that is not a set (due to not bein ordered without duplicates).

std.setDiff(a, b)

Set difference operation (values in a but not b).

Encoding

std.base64(v)

Encodes the given value into a base64 string. The encoding sequence is A-Za-z0-9+/ with = to pad the output to a multiple of 4 characters. The value can be a string or an array of numbers, but the codepoints / numbers must be in the 0 to 255 range. The resulting string has no line breaks.

std.base64DecodeBytes(s)

Decodes the given base64 string into an array of bytes (number values). Currently assumes the input string has no linebreaks and is padded to a multiple of 4 (with the = character). In other words, it consumes the output of std.base64().

std.base64Decode(s)

Behaves like std.base64DecodeBytes() except returns a string instead of an array of bytes.

std.md5(s)

Encodes the given value into an MD5 string.

JSON Merge Patch

std.mergePatch(target, patch)

Applies patch to target according to RFC7396