Programming inevitably needs to write configuration files. How to write configuration is also a knowledge. YAML language (pronunciation)/ ˈ jæm ə l /) is designed to facilitate human reading and writing. It is essentially a universal data serialization format.
YAML is a language specially used to write configuration files. It is very concise and powerful, which is far more convenient than JSON format.
This paper introduces the syntax of YAML to JS-YAML As an example. You can go Online Demo Verify the following example.
Its basic syntax rules are as follows.
- Case sensitive
- Use indents to indicate hierarchical relationships
- The Tab key is not allowed when indenting, only spaces are allowed.
- The number of indented spaces is not important, as long as the elements of the same level are aligned to the left
#Represents a comment. From this character to the end of the line, it will be ignored by the parser.
YAML supports three data structures.
- Object: a collection of key value pairs, also known as mapping / hashes / dictionary
- Array: a set of values arranged in order, also known as sequence / list
- scalars: single, non separable value
These three data structures are described below.
2, Object
A set of key value pairs of an object, represented by a colon structure.
animal: pets
Convert to JavaScript as follows.
{ animal: 'pets' }
Yaml also allows another way to write all key value pairs as an inline object.
hash: { name: Steve, foo: bar }
Convert to JavaScript as follows.
{ hash: { name: 'Steve', foo: 'bar' } }
3, Array
A set of lines beginning with a conjunction line to form an array.
- Cat - Dog - Goldfish
Convert to JavaScript as follows.
[ 'Cat', 'Dog', 'Goldfish' ]
If the child member of the data structure is an array, you can indent a space under the item.
- - Cat - Dog - Goldfish
Convert to JavaScript as follows.
[ [ 'Cat', 'Dog', 'Goldfish' ] ]
Arrays can also use inline representation.
animal: [Cat, Dog]
Convert to JavaScript as follows.
{ animal: [ 'Cat', 'Dog' ] }
4, Composite structure
Objects and arrays can be used together to form a composite structure.
languages: - Ruby - Perl - Python websites: YAML: yaml.org Ruby: ruby-lang.org Python: python.org Perl: use.perl.org
Convert to JavaScript as follows.
{ languages: [ 'Ruby', 'Perl', 'Python' ],
websites:
{ YAML: 'yaml.org',
Ruby: 'ruby-lang.org',
Python: 'python.org',
Perl: 'use.perl.org' } }
5, Pure quantity
Scalar is the most basic and inseparable value. The following data types are scalars of JavaScript.
- character string
- Boolean value
- integer
- Floating point number
- Null
- time
- date
Values are expressed directly in literal form.
number: 12.30
Convert to JavaScript as follows.
{ number: 12.30 }
Boolean values are represented by true and false.
isSet: true
Convert to JavaScript as follows.
{ isSet: true }
null is represented by ~.
parent: ~
Convert to JavaScript as follows.
{ parent: null }
The time is in ISO8601 format.
iso8601: 2001-12-14t21:59:43.10-05:00
Convert to JavaScript as follows.
{ iso8601: new Date('2001-12-14t21:59:43.10-05:00') }
The date is represented by year, month and day in compound iso8601 format.
date: 1976-07-31
Convert to JavaScript as follows.
{ date: new Date('1976-07-31') }
YAML allows the use of two exclamation marks to cast data types.
e: !!str 123 f: !!str true
Convert to JavaScript as follows.
{ e: '123', f: 'true' }
6, String
String is the most common and complex data type.
Strings are not quoted by default.
str: This is a line of string
Convert to JavaScript as follows.
{ str: 'This is a line of string' }
If the string contains spaces or special characters, you need to put them in quotation marks.
str: 'Content: String'
Convert to JavaScript as follows.
{ str: 'content: character string' }
Single quotation marks and double quotation marks can be used, and double quotation marks will not escape special characters.
s1: 'content\n character string' s2: "content\n character string"
Convert to JavaScript as follows.
{ s1: 'content\\n character string', s2: 'content\n character string' }
If there are single quotation marks in single quotation marks, two single quotation marks must be used continuously to escape.
str: 'labor''s day'
Convert to JavaScript as follows.
{ str: 'labor\'s day' }
The string can be written in multiple lines. Starting from the second line, there must be a single space indentation. Line breaks are converted to spaces.
str: This is a paragraph Multiline character string
Convert to JavaScript as follows.
{ str: 'This is a multiline string' }
For multiline strings, you can use | to preserve line breaks or > to collapse line breaks.
this: | Foo Bar that: > Foo Bar
The code to JavaScript is as follows.
{ this: 'Foo\nBar\n', that: 'Foo Bar\n' }
+Means to keep the line break at the end of the text block, - means to delete the line break at the end of the string.
s1: | Foo s2: |+ Foo s3: |- Foo
The code to JavaScript is as follows.
{ s1: 'Foo\n', s2: 'Foo\n\n\n', s3: 'Foo' }
HTML tags can be inserted into the string.
message: |
<p style="color: red">
paragraph
</p>
Convert to JavaScript as follows.
{ message: '\n<p style="color: red">\n paragraph\n</p>\n' }
7, Quote
Anchor & and alias *, which can be used to reference.
defaults: &defaults adapter: postgres host: localhost development: database: myapp_development <<: *defaults test: database: myapp_test <<: *defaults
Equivalent to the following code.
defaults: adapter: postgres host: localhost development: database: myapp_development adapter: postgres host: localhost test: database: myapp_test adapter: postgres host: localhost
&It is used to establish anchors, < < indicates merging into the current data, * is used to reference anchors.
Here is another example.
- &showell Steve - Clark - Brian - Oren - *showell
The code to JavaScript is as follows.
[ 'Steve', 'Clark', 'Brian', 'Oren', 'Steve' ]
8, Conversion of functions and regular expressions
This is JS-YAML Library specific functions can convert functions and regular expressions into strings.
# example.yml
fn: function () { return 1 }
reg: /test/
The code for parsing the above yml file is as follows.
var yaml = require('js-yaml');
var fs = require('fs');
try {
var doc = yaml.load(
fs.readFileSync('./example.yml', 'utf8')
);
console.log(doc);
} catch (e) {
console.log(e);
}
The code to restore the JavaScript object to the yaml file is as follows.
var yaml = require('js-yaml');
var fs = require('fs');
var obj = {
fn: function () { return 1 },
reg: /test/
};
try {
fs.writeFileSync(
'./example.yml',
yaml.dump(obj),
'utf8'
);
} catch (e) {
console.log(e);
}
9, Reference link
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