%Q, %q, %W, %w, %x, %r, %s, %i

Perl-inspired notation to quote strings: by using % (percent character) and specifying a delimiting character.

Any single non-alpha-numeric character can be used as the delimiter, %[including these], %?or these?, %~or even these things~.

Strings

% or %Q

Use %Q only for strings that contain both single quotes and double quotes, or for dynamic strings that contain double quotes.

interpolated string

This is an alternative for double-quoted strings, when you have more quote characters in a string.Instead of putting backslashes in front of them, you can easily write:

>> %Q(Joe said: "Frank said: "#{what_frank_said}"")
=> "Joe said: "Frank said: "Hello!"""

The parenthesis “(…)” can be replaced with any other non-alphanumeric characters and non-printing characters (pairs), so the following commands are equivalent:

>> %Q!Joe said: "Frank said: "#{what_frank_said}""!
>> %Q[Joe said: "Frank said: "#{what_frank_said}""]
>> %Q+Joe said: "Frank said: "#{what_frank_said}""+

You can use also:

>> %/Joe said: "Frank said: "#{what_frank_said}""/
=> "Joe said: "Frank said: "Hello!"""

%q

non-interpolated string

Used for single-quoted strings.The syntax is similar to %Q, but single-quoted strings are not subject to expression substitution or escape sequences.

>> %q(Joe said: 'Frank said: '#{what_frank_said} ' ')
=> "Joe said: 'Frank said: '\#{what_frank_said} ' '"

Arrays

%W

interpolated array of words, separated by whitespace

Used for double-quoted array elements.The syntax is similar to %Q

>> %W(#{foo} Bar Bar\ with\ space)
=> ["Foo", "Bar", "Bar with space"]

%w

non-interpolated array of words, separated by whitespace

Used for single-quoted array elements. The syntax is similar to %Q, but single-quoted elements are not subject to expression substitution or escape sequences.

>> %w(#{foo} Bar Bar\ with\ space)
=> ["\#{foo}", "Bar", "Bar with space"]

%I

interpolated array of symbols, separated by whitespace

Generates an array of symbols, similar to %W, available in ruby >= 2.1.

>> %I(#{foo} Bar Bar\ with\ space)
=> => [:foo, :Bar, :"Bar with space"]

%i

non-interpolated array of symbols, separated by whitespace

Generates an array of symbols, similar to %W, available in ruby >= 2.1.

>> %I(#{foo} Bar Bar\ with\ space)
=> [:"\#{foo}", :Bar, :"Bar with space"]

Symbols

%s

interpolated string

Used for symbols. It’s not subject to expression substitution or escape sequences.

>> %s(foo)
=> :foo

>> %s(foo bar)
=> :"foo bar"

>> %s(#{foo} bar)
=> :"\#{foo} bar"

Shell command

%x

interpolated shell command

Uses the ` method and returns the standard output of running the command in a subshell.The syntax is similar to %Q.

>> %x(echo foo:#{foo})
=> "foo:Foo\n"

Regexp

%r

interpolated regexp

Used for regular expressions.The syntax is similar to %Q.

>> %r(/home/#{foo})
=> "/\\/home\\/Foo/"

Additionnaly, you can add flags after the closing delimiter, like this

>> %r/[a-z]/i
=> /[a-z]/i