1# YAML support for the Go language
2
3Introduction
4------------
5
6The yaml package enables Go programs to comfortably encode and decode YAML
7values. It was developed within [Canonical](https://www.canonical.com) as
8part of the [juju](https://juju.ubuntu.com) project, and is based on a
9pure Go port of the well-known [libyaml](http://pyyaml.org/wiki/LibYAML)
10C library to parse and generate YAML data quickly and reliably.
11
12Compatibility
13-------------
14
15The yaml package supports most of YAML 1.2, but preserves some behavior
16from 1.1 for backwards compatibility.
17
18Specifically, as of v3 of the yaml package:
19
20 - YAML 1.1 bools (_yes/no, on/off_) are supported as long as they are being
21 decoded into a typed bool value. Otherwise they behave as a string. Booleans
22 in YAML 1.2 are _true/false_ only.
23 - Octals encode and decode as _0777_ per YAML 1.1, rather than _0o777_
24 as specified in YAML 1.2, because most parsers still use the old format.
25 Octals in the _0o777_ format are supported though, so new files work.
26 - Does not support base-60 floats. These are gone from YAML 1.2, and were
27 actually never supported by this package as it's clearly a poor choice.
28
29and offers backwards
30compatibility with YAML 1.1 in some cases.
311.2, including support for
32anchors, tags, map merging, etc. Multi-document unmarshalling is not yet
33implemented, and base-60 floats from YAML 1.1 are purposefully not
34supported since they're a poor design and are gone in YAML 1.2.
35
36Installation and usage
37----------------------
38
39The import path for the package is *gopkg.in/yaml.v3*.
40
41To install it, run:
42
43 go get gopkg.in/yaml.v3
44
45API documentation
46-----------------
47
48If opened in a browser, the import path itself leads to the API documentation:
49
50 - [https://gopkg.in/yaml.v3](https://gopkg.in/yaml.v3)
51
52API stability
53-------------
54
55The package API for yaml v3 will remain stable as described in [gopkg.in](https://gopkg.in).
56
57
58License
59-------
60
61The yaml package is licensed under the MIT and Apache License 2.0 licenses.
62Please see the LICENSE file for details.
63
64
65Example
66-------
67
68```Go
69package main
70
71import (
72 "fmt"
73 "log"
74
75 "gopkg.in/yaml.v3"
76)
77
78var data = `
79a: Easy!
80b:
81 c: 2
82 d: [3, 4]
83`
84
85// Note: struct fields must be public in order for unmarshal to
86// correctly populate the data.
87type T struct {
88 A string
89 B struct {
90 RenamedC int `yaml:"c"`
91 D []int `yaml:",flow"`
92 }
93}
94
95func main() {
96 t := T{}
97
98 err := yaml.Unmarshal([]byte(data), &t)
99 if err != nil {
100 log.Fatalf("error: %v", err)
101 }
102 fmt.Printf("--- t:\n%v\n\n", t)
103
104 d, err := yaml.Marshal(&t)
105 if err != nil {
106 log.Fatalf("error: %v", err)
107 }
108 fmt.Printf("--- t dump:\n%s\n\n", string(d))
109
110 m := make(map[interface{}]interface{})
111
112 err = yaml.Unmarshal([]byte(data), &m)
113 if err != nil {
114 log.Fatalf("error: %v", err)
115 }
116 fmt.Printf("--- m:\n%v\n\n", m)
117
118 d, err = yaml.Marshal(&m)
119 if err != nil {
120 log.Fatalf("error: %v", err)
121 }
122 fmt.Printf("--- m dump:\n%s\n\n", string(d))
123}
124```
125
126This example will generate the following output:
127
128```
129--- t:
130{Easy! {2 [3 4]}}
131
132--- t dump:
133a: Easy!
134b:
135 c: 2
136 d: [3, 4]
137
138
139--- m:
140map[a:Easy! b:map[c:2 d:[3 4]]]
141
142--- m dump:
143a: Easy!
144b:
145 c: 2
146 d:
147 - 3
148 - 4
149```
150
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