The YAML Format ¶

Strings ¶

Strings in YAML can be wrapped both in single and double quotes. In some cases, they can also be unquoted:

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A string in YAML

'A single-quoted string in YAML'

"A double-quoted string in YAML"

Quoted styles are useful when a string starts or end with one or more relevant spaces, because unquoted strings are trimmed on both end when parsing their contents. Quotes are required when the string contains special or reserved characters.

When using single-quoted strings, any single quote ' inside its contents must be doubled to escape it:

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'A single quote '' inside a single-quoted string'

Strings containing any of the following characters must be quoted. Although you can use double quotes, for these characters it is more convenient to use single quotes, which avoids having to escape any backslash \:

• :, {, }, [, ], ,, &, *, #, ?, |, -, <, >, =, !, %, @, `

The double-quoted style provides a way to express arbitrary strings, by using \ to escape characters and sequences. For instance, it is very useful when you need to embed a \n or a Unicode character in a string.

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"A double-quoted string in YAML\n"

If the string contains any of the following control characters, it must be escaped with double quotes:

• \0, \x01, \x02, \x03, \x04, \x05, \x06, \a, \b, \t, \n, \v, \f, \r, \x0e, \x0f, \x10, \x11, \x12, \x13, \x14, \x15, \x16, \x17, \x18, \x19, \x1a, \e, \x1c, \x1d, \x1e, \x1f, \N, \_, \L, \P
  \0、\x01、\x02、\x03、\x04、\x05、\x06、\a、\b、\t、\n、\v、\f、\r、\x0e、\x0f、\x10 ,\x11, \x12, \x13, \x14, \x15, \x16, \x17, \x18,\x19, \x1a, \e, \x1c, \x1d, \x1e, \x1f, \N,\ _、\L、\P

Finally, there are other cases when the strings must be quoted, no matter if you're using single or double quotes:

• When the string is true or false (otherwise, it would be treated as a boolean value);
  文字列が true または false の場合 (そうでない場合は、ブール値として扱われます)。
• When the string is null or ~ (otherwise, it would be considered as a null value);
  文字列が null または ~ の場合 (そうでない場合は、null 値と見なされます)。
• When the string looks like a number, such as integers (e.g. 2, 14, etc.), floats (e.g. 2.6, 14.9) and exponential numbers (e.g. 12e7, etc.) (otherwise, it would be treated as a numeric value);
  整数（2、14 など）、浮動小数点数（2.6、14.9 など）、指数（12e7 など）など、文字列が数値のように見える場合（それ以外の場合は、数値として扱われます） ;
• When the string looks like a date (e.g. 2014-12-31) (otherwise it would be automatically converted into a Unix timestamp).
  文字列が日付のように見える場合 (例: 2014-12-31) (それ以外の場合は、Unix タイムスタンプに自動的に変換されます)。

When a string contains line breaks, you can use the literal style, indicated by the pipe (|), to indicate that the string will span several lines. In literals, newlines are preserved:

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|
  \/ /| |\/| |
  / / | |  | |__

Alternatively, strings can be written with the folded style, denoted by >, where each line break is replaced by a space:

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>
  This is a very long sentence
  that spans several lines in the YAML.

# This will be parsed as follows: (notice the trailing \n)
# "This is a very long sentence that spans several lines in the YAML.\n"

>-
  This is a very long sentence
  that spans several lines in the YAML.

# This will be parsed as follows: (without a trailing \n)
# "This is a very long sentence that spans several lines in the YAML."

Numbers ¶

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# an integer
12

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# an octal
0o14

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# an hexadecimal
0xC

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# a float
13.4

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# an exponential number
1.2e+34

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# infinity
.inf

Nulls ¶

Nulls in YAML can be expressed with null or ~.

Booleans ¶

Booleans in YAML are expressed with true and false.

Dates ¶

YAML uses the ISO-8601 standard to express dates:

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2001-12-14T21:59:43.10-05:00

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# simple date
2002-12-14