# Literals¶ ↑

Literals create objects you can use in your program. Literals include:

## Boolean and Nil Literals¶ ↑

`nil` and `false` are both false values. `nil` is sometimes used to indicate “no value” or “unknown” but evaluates to `false` in conditional expressions.

`true` is a true value. All objects except `nil` and `false` evaluate to a true value in conditional expressions.

## Number Literals¶ ↑

### Integer Literals¶ ↑

You can write integers of any size as follows:

```1234
1_234
```

These numbers have the same value, 1,234. The underscore may be used to enhance readability for humans. You may place an underscore anywhere in the number.

You can use a special prefix to write numbers in decimal, hexadecimal, octal or binary formats. For decimal numbers use a prefix of `0d`, for hexadecimal numbers use a prefix of `0x`, for octal numbers use a prefix of `0` or `0o`, for binary numbers use a prefix of `0b`. The alphabetic component of the number is not case-sensitive.

Examples:

```0d170
0D170

0xaa
0xAa
0xAA
0Xaa
0XAa
0XaA

0252
0o252
0O252

0b10101010
0B10101010
```

All these numbers have the same decimal value, 170. Like integers and floats you may use an underscore for readability.

### Float Literals¶ ↑

Floating-point numbers may be written as follows:

```12.34
1234e-2
1.234E1
```

These numbers have the same value, 12.34. You may use underscores in floating point numbers as well.

### Rational Literals¶ ↑

You can write a `Rational` literal using a special suffix, `'r'`.

Examples:

```1r       # => (1/1)
2/3r     # => (2/3)   # With denominator.
-1r      # => (-1/1)  # With signs.
-2/3r    # => (-2/3)
2/-3r    # => (-2/3)
-2/-3r   # => (2/3)
+1/+3r   # => (1/3)
1.2r     # => (6/5)   # With fractional part.
1_1/2_1r # => (11/21) # With embedded underscores.
2/4r     # => (1/2)   # Automatically reduced.
```

Syntax:

```<rational-literal> = <numerator> [ '/' <denominator> ] 'r'
<numerator> = [ <sign> ] <digits> [ <fractional-part> ]
<fractional-part> = '.' <digits>
<denominator> = [ sign ] <digits>
<sign> = '-' | '+'
<digits> = <digit> { <digit> | '_' <digit> }
<digit> = '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9'```

Note this, which is parsed as Float numerator `1.2` divided by Rational denominator `3r`, resulting in a Float:

```1.2/3r  # => 0.39999999999999997
```

### Complex Literals¶ ↑

You can write a `Complex` number as follows (suffixed `i`):

```1i          #=> (0+1i)
1i * 1i     #=> (-1+0i)
```

Also Rational numbers may be imaginary numbers.

```12.3ri      #=> (0+(123/10)*i)
```

`i` must be placed after `r`; the opposite is not allowed.

`12.3ir      #=> Syntax error`

## Strings¶ ↑

### Escape Sequences¶ ↑

Some characters can be represented as escape sequences in double-quoted strings, character literals, here document literals (non-quoted, double-quoted, and with backticks), double-quoted symbols, double-quoted symbol keys in `Hash` literals, `Regexp` literals, and several percent literals (`%`, `%Q,` `%W`, `%I`, `%r`, `%x`).

They allow escape sequences such as `\n` for newline, `\t` for tab, etc. The full list of supported escape sequences are as follows:

```\a             bell, ASCII 07h (BEL)
\b             backspace, ASCII 08h (BS)
\t             horizontal tab, ASCII 09h (TAB)
\n             newline (line feed), ASCII 0Ah (LF)
\v             vertical tab, ASCII 0Bh (VT)
\f             form feed, ASCII 0Ch (FF)
\r             carriage return, ASCII 0Dh (CR)
\e             escape, ASCII 1Bh (ESC)
\s             space, ASCII 20h (SPC)
\\             backslash, \
\nnn           octal bit pattern, where nnn is 1-3 octal digits ([0-7])
\unnnn         Unicode character, where nnnn is exactly 4 hexadecimal digits ([0-9a-fA-F])
\u{nnnn ...}   Unicode character(s), where each nnnn is 1-6 hexadecimal digits ([0-9a-fA-F])
\cx or \C-x    control character, where x is an ASCII printable character
\M-x           meta character, where x is an ASCII printable character
\M-\C-x        meta control character, where x is an ASCII printable character
\M-\cx         same as above
\c\M-x         same as above
\c? or \C-?    delete, ASCII 7Fh (DEL)
\<newline>     continuation line (empty string)```

The last one, `<newline>`, represents an empty string instead of a character. It is used to fold a line in a string.

### Double-quoted String Literals¶ ↑

The most common way of writing strings is using `"`:

```"This is a string."
```

The string may be many lines long.

Any internal `"` must be escaped:

```"This string has a quote: \".  As you can see, it is escaped"
```

Double-quoted strings allow escape sequences described in Escape Sequences.

In a double-quoted string, any other character following a backslash is interpreted as the character itself.

Double-quoted strings allow interpolation of other values using `#{...}`:

```"One plus one is two: #{1 + 1}"
```

Any expression may be placed inside the interpolated section, but it’s best to keep the expression small for readability.

You can also use `#@foo`, `#@@foo` and `#\$foo` as a shorthand for, respectively, `#{ @foo }`, `#{ @@foo }` and `#{ \$foo }`.

### Single-quoted String Literals¶ ↑

Interpolation may be disabled by escaping the “#” character or using single-quoted strings:

```'#{1 + 1}' #=> "\#{1 + 1}"
```

In addition to disabling interpolation, single-quoted strings also disable all escape sequences except for the single-quote (`\'`) and backslash (`\\`).

In a single-quoted string, any other character following a backslash is interpreted as is: a backslash and the character itself.

### Literal `String` Concatenation¶ ↑

Adjacent string literals are automatically concatenated by the interpreter:

```"con" "cat" "en" "at" "ion" #=> "concatenation"
"This string contains "\
"no newlines."              #=> "This string contains no newlines."
```

Any combination of adjacent single-quote, double-quote, percent strings will be concatenated as long as a percent-string is not last.

```%q{a} 'b' "c" #=> "abc"
"a" 'b' %q{c} #=> NameError: uninitialized constant q
```

### Character Literal¶ ↑

There is also a character literal notation to represent single character strings, which syntax is a question mark (`?`) followed by a single character or escape sequence (except continuation line) that corresponds to a single codepoint in the script encoding:

```?a       #=> "a"
?abc     #=> SyntaxError
?\n      #=> "\n"
?\s      #=> " "
?\\      #=> "\\"
?\u{41}  #=> "A"
?\C-a    #=> "\x01"
?\M-a    #=> "\xE1"
?\M-\C-a #=> "\x81"
?\C-\M-a #=> "\x81", same as above
?あ      #=> "あ"```

### Here Document Literals¶ ↑

If you are writing a large block of text you may use a “here document” or “heredoc”:

```expected_result = <<HEREDOC
This would contain specially formatted text.

That might span many lines
HEREDOC
```

The heredoc starts on the line following `<<HEREDOC` and ends with the next line that starts with `HEREDOC`. The result includes the ending newline.

You may use any identifier with a heredoc, but all-uppercase identifiers are typically used.

You may indent the ending identifier if you place a “-” after `<<`:

```  expected_result = <<-INDENTED_HEREDOC
This would contain specially formatted text.

That might span many lines
INDENTED_HEREDOC
```

Note that while the closing identifier may be indented, the content is always treated as if it is flush left. If you indent the content those spaces will appear in the output.

To have indented content as well as an indented closing identifier, you can use a “squiggly” heredoc, which uses a “~” instead of a “-” after `<<`:

```expected_result = <<~SQUIGGLY_HEREDOC
This would contain specially formatted text.

That might span many lines
SQUIGGLY_HEREDOC
```

The indentation of the least-indented line will be removed from each line of the content. Note that empty lines and lines consisting solely of literal tabs and spaces will be ignored for the purposes of determining indentation, but escaped tabs and spaces are considered non-indentation characters.

For the purpose of measuring an indentation, a horizontal tab is regarded as a sequence of one to eight spaces such that the column position corresponding to its end is a multiple of eight. The amount to be removed is counted in terms of the number of spaces. If the boundary appears in the middle of a tab, that tab is not removed.

A heredoc allows interpolation and the escape sequences described in Escape Sequences. You may disable interpolation and the escaping by surrounding the opening identifier with single quotes:

```expected_result = <<-'EXPECTED'
One plus one is #{1 + 1}
EXPECTED

p expected_result # prints: "One plus one is \#{1 + 1}\n"
```

The identifier may also be surrounded with double quotes (which is the same as no quotes) or with backticks. When surrounded by backticks the HEREDOC behaves like `Kernel#``:

```puts <<-`HEREDOC`
cat #{__FILE__}
HEREDOC
```

When surrounding with quotes, any character but that quote and newline (CR and/or LF) can be used as the identifier.

To call a method on a heredoc place it after the opening identifier:

```expected_result = <<-EXPECTED.chomp
One plus one is #{1 + 1}
EXPECTED
```

You may open multiple heredocs on the same line, but this can be difficult to read:

```puts(<<-ONE, <<-TWO)
content for heredoc one
ONE
content for heredoc two
TWO
```

## Symbol Literals¶ ↑

A `Symbol` represents a name inside the ruby interpreter. See `Symbol` for more details on what symbols are and when ruby creates them internally.

You may reference a symbol using a colon: `:my_symbol`.

You may also create symbols by interpolation and escape sequences described in Escape Sequences with double-quotes:

```:"my_symbol1"
:"my_symbol#{1 + 1}"
:"foo\sbar"
```

Like strings, a single-quote may be used to disable interpolation and escape sequences:

```:'my_symbol#{1 + 1}' #=> :"my_symbol\#{1 + 1}"
```

When creating a `Hash`, there is a special syntax for referencing a `Symbol` as well.

## Array Literals¶ ↑

An array is created using the objects between `[` and `]`:

```[1, 2, 3]
```

You may place expressions inside the array:

```[1, 1 + 1, 1 + 2]
[1, [1 + 1, [1 + 2]]]
```

See `Array` for the methods you may use with an array.

## Hash Literals¶ ↑

A hash is created using key-value pairs between `{` and `}`:

```{ "a" => 1, "b" => 2 }
```

Both the key and value may be any object.

You can create a hash using symbol keys with the following syntax:

```{ a: 1, b: 2 }
```

This same syntax is used for keyword arguments for a method.

Like `Symbol` literals, you can quote symbol keys.

```{ "a 1": 1, "b #{1 + 1}": 2 }
```

is equal to

```{ :"a 1" => 1, :"b 2" => 2 }
```

`Hash` values can be omitted, meaning that value will be fetched from the context by the name of the key:

```x = 100
y = 200
h = { x:, y: }
#=> {:x=>100, :y=>200}
```

See `Hash` for the methods you may use with a hash.

## Range Literals¶ ↑

A range represents an interval of values. The range may include or exclude its ending value.

```(1..2)  # includes its ending value
(1...2) # excludes its ending value
(1..)   # endless range, representing infinite sequence from 1 to Infinity
(..1)   # beginless range, representing infinite sequence from -Infinity to 1
```

You may create a range of any object. See the `Range` documentation for details on the methods you need to implement.

## Regexp Literals¶ ↑

A regular expression may be created using leading and trailing slash (`'/'`) characters:

```re = /foo/ # => /foo/
re.class   # => Regexp
```

The trailing slash may be followed by one or more modifiers characters that set modes for the regexp. See Regexp modes for details.

Interpolation may be used inside regular expressions along with escaped characters. Note that a regular expression may require additional escaped characters than a string.

See `Regexp` for a description of the syntax of regular expressions.

## Lambda `Proc` Literals¶ ↑

A lambda proc can be created with `->`:

```-> { 1 + 1 }
```

Calling the above proc will give a result of `2`.

You can require arguments for the proc as follows:

```->(v) { 1 + v }
```

This proc will add one to its argument.

## Percent Literals¶ ↑

Each of the literals in described in this section may use these paired delimiters:

• `[` and `]`.

• `(` and `)`.

• `{` and `}`.

• `<` and `>`.

• Non-alphanumeric ASCII character except above, as both beginning and ending delimiters.

The delimiters can be escaped with a backslash. However, the first four pairs (brackets, parenthesis, braces, and angle brackets) are allowed without backslash as far as they are correctly paired.

These are demonstrated in the next section.

### `%q`: Non-Interpolable `String` Literals¶ ↑

You can write a non-interpolable string with `%q`. The created string is the same as if you created it with single quotes:

```%q[foo bar baz]       # => "foo bar baz" # Using [].
%q(foo bar baz)       # => "foo bar baz" # Using ().
%q{foo bar baz}       # => "foo bar baz" # Using {}.
%q<foo bar baz>       # => "foo bar baz" # Using <>.
%q|foo bar baz|       # => "foo bar baz" # Using two |.
%q:foo bar baz:       # => "foo bar baz" # Using two :.
%q(1 + 1 is #{1 + 1}) # => "1 + 1 is \#{1 + 1}" # No interpolation.
%q[foo[bar]baz]       # => "foo[bar]baz" # brackets can be nested.
%q(foo(bar)baz)       # => "foo(bar)baz" # parenthesis can be nested.
%q{foo{bar}baz}       # => "foo{bar}baz" # braces can be nested.
%q<foo<bar>baz>       # => "foo<bar>baz" # angle brackets can be nested.
```

This is similar to single-quoted string but only backslashs and the specified delimiters can be escaped with a backslash.

### `% and %Q`: Interpolable `String` Literals¶ ↑

You can write an interpolable string with `%Q` or with its alias `%`:

```%[foo bar baz]       # => "foo bar baz"
%(1 + 1 is #{1 + 1}) # => "1 + 1 is 2" # Interpolation.
```

This is similar to double-quoted string. It allow escape sequences described in Escape Sequences. Other escaped characters (a backslash followed by a character) are interpreted as the character.

### `%w and %W`: String-Array Literals¶ ↑

You can write an array of strings as whitespace-separated words with `%w` (non-interpolable) or `%W` (interpolable):

```%w[foo bar baz]       # => ["foo", "bar", "baz"]
%w[1 % *]             # => ["1", "%", "*"]
# Use backslash to embed spaces in the strings.
%w[foo\ bar baz\ bat] # => ["foo bar", "baz bat"]
%W[foo\ bar baz\ bat] # => ["foo bar", "baz bat"]
%w(#{1 + 1})          # => ["\#{1", "+", "1}"]
%W(#{1 + 1})          # => ["2"]

# The nested delimiters evaluated to a flat array of strings
# (not nested array).
%w[foo[bar baz]qux]   # => ["foo[bar", "baz]qux"]
```

The following characters are considered as white spaces to separate words:

• space, ASCII 20h (SPC)

• form feed, ASCII 0Ch (FF)

• newline (line feed), ASCII 0Ah (LF)

• carriage return, ASCII 0Dh (CR)

• horizontal tab, ASCII 09h (TAB)

• vertical tab, ASCII 0Bh (VT)

The white space characters can be escaped with a backslash to make them part of a word.

`%W` allow escape sequences described in Escape Sequences. However the continuation line `<newline>` is not usable because it is interpreted as the escaped newline described above.

### `%i and %I`: Symbol-Array Literals¶ ↑

You can write an array of symbols as whitespace-separated words with `%i` (non-interpolable) or `%I` (interpolable):

```%i[foo bar baz]       # => [:foo, :bar, :baz]
%i[1 % *]             # => [:"1", :%, :*]
# Use backslash to embed spaces in the symbols.
%i[foo\ bar baz\ bat] # => [:"foo bar", :"baz bat"]
%I[foo\ bar baz\ bat] # => [:"foo bar", :"baz bat"]
%i(#{1 + 1})          # => [:"\#{1", :+, :"1}"]
%I(#{1 + 1})          # => [:"2"]
```

The white space characters and its escapes are interpreted as the same as string-array literals described in %w and %W: String-Array Literals.

### `%s`: `Symbol` Literals¶ ↑

You can write a symbol with `%s`:

```%s[foo]     # => :foo
%s[foo bar] # => :"foo bar"
```

This is non-interpolable. No interpolation allowed. Only backslashs and the specified delimiters can be escaped with a backslash.

### `%r`: `Regexp` Literals¶ ↑

You can write a regular expression with `%r`; the character used as the leading and trailing delimiter may be (almost) any character:

```%r/foo/             # => /foo/
%r:name/value pair: # => /name\/value pair/
```

A few “symmetrical” character pairs may be used as delimiters:

```%r[foo] # => /foo/
%r{foo} # => /foo/
%r(foo) # => /foo/
%r<foo> # => /foo/
```

The trailing delimiter may be followed by one or more modifier characters that set modes for the regexp. See Regexp modes for details.

### `%x`: Backtick Literals¶ ↑

You can write and execute a shell command with `%x`:

```%x(echo 1)      # => "1\n"
%x[echo #{1 + 2}] # => "3\n"
%x[echo \u0030] # => "0\n"
```

This is interpolable. `%x` allow escape sequences described in Escape Sequences.