Symbol objects represent names inside the Ruby interpreter. They are generated using the
:"string" literals syntax, and by the various
to_sym methods. The same Symbol object will be created for a given name or string for the duration of a program’s execution, regardless of the context or meaning of that name. Thus if
Fred is a constant in one context, a method in another, and a class in a third, the Symbol
:Fred will be the same object in all three contexts.
module One class Fred end $f1 = :Fred end module Two Fred = 1 $f2 = :Fred end def Fred() end $f3 = :Fred $f1.object_id #=> 2514190 $f2.object_id #=> 2514190 $f3.object_id #=> 2514190
A String object holds and manipulates an arbitrary sequence of bytes, typically representing characters. String objects may be created using String::new or as literals.
Because of aliasing issues, users of strings should be aware of the methods that modify the contents of a String object. Typically, methods with names ending in
! modify their receiver, while those without a
! return a new String. However, there are exceptions, such as
An Encoding instance represents a character encoding usable in Ruby. It is defined as a constant under the Encoding namespace. It has a name and optionally, aliases:
Encoding::ISO_8859_1.name #=> "ISO-8859-1" Encoding::ISO_8859_1.names #=> ["ISO-8859-1", "ISO8859-1"]
Ruby methods dealing with encodings return or accept Encoding instances as arguments (when a method accepts an Encoding instance as an argument, it can be passed an Encoding name or alias instead).
"some string".encoding #=> #<Encoding:UTF-8> string = "some string".encode(Encoding::ISO_8859_1) #=> "some string" string.encoding #=> #<Encoding:ISO-8859-1> "some string".encode "ISO-8859-1" #=> "some string"
Encoding::ASCII_8BIT is a special encoding that is usually used for a byte string, not a character string. But as the name insists, its characters in the range of ASCII are considered as ASCII characters. This is useful when you use ASCII-8BIT characters with other ASCII compatible characters.
The associated Encoding of a String can be changed in two different ways.
First, it is possible to set the Encoding of a string to a new Encoding without changing the internal byte representation of the string, with
String#force_encoding. This is how you can tell Ruby the correct encoding of a string.
string #=> "R\xC3\xA9sum\xC3\xA9" string.encoding #=> #<Encoding:ISO-8859-1> string.force_encoding(Encoding::UTF_8) #=> "R\u00E9sum\u00E9"
Second, it is possible to transcode a string, i.e. translate its internal byte representation to another encoding. Its associated encoding is also set to the other encoding. See
String#encode for the various forms of transcoding, and the Encoding::Converter class for additional control over the transcoding process.
string #=> "R\u00E9sum\u00E9" string.encoding #=> #<Encoding:UTF-8> string = string.encode!(Encoding::ISO_8859_1) #=> "R\xE9sum\xE9" string.encoding #=> #<Encoding::ISO-8859-1>
All Ruby script code has an associated Encoding which any String literal created in the source code will be associated to.
The default script encoding is Encoding::UTF_8 after v2.0, but it can be changed by a magic comment on the first line of the source code file (or second line, if there is a shebang line on the first). The comment must contain the word
encoding, followed by a colon, space and the Encoding name or alias:
# encoding: UTF-8 "some string".encoding #=> #<Encoding:UTF-8>
__ENCODING__ keyword returns the script encoding of the file which the keyword is written:
# encoding: ISO-8859-1 __ENCODING__ #=> #<Encoding:ISO-8859-1>
ruby -K will change the default locale encoding, but this is not recommended. Ruby source files should declare its script encoding by a magic comment even when they only depend on US-ASCII strings or regular expressions.
The default encoding of the environment. Usually derived from locale.
see Encoding.locale_charmap, Encoding.find(‘locale’)
The default encoding of strings from the filesystem of the environment. This is used for strings of file names or paths.
Each IO object has an external encoding which indicates the encoding that Ruby will use to read its data. By default Ruby sets the external encoding of an IO object to the default external encoding. The default external encoding is set by locale encoding or the interpreter
-E option. Encoding.default_external returns the current value of the external encoding.
ENV["LANG"] #=> "UTF-8" Encoding.default_external #=> #<Encoding:UTF-8> $ ruby -E ISO-8859-1 -e "p Encoding.default_external" #<Encoding:ISO-8859-1> $ LANG=C ruby -e 'p Encoding.default_external' #<Encoding:US-ASCII>
The default external encoding may also be set through Encoding.default_external=, but you should not do this as strings created before and after the change will have inconsistent encodings. Instead use
ruby -E to invoke ruby with the correct external encoding.
When you know that the actual encoding of the data of an IO object is not the default external encoding, you can reset its external encoding with
IO#set_encoding or set it at IO object creation (see IO.new options).
To process the data of an IO object which has an encoding different from its external encoding, you can set its internal encoding. Ruby will use this internal encoding to transcode the data when it is read from the IO object.
Conversely, when data is written to the IO object it is transcoded from the internal encoding to the external encoding of the IO object.
The internal encoding of an IO object can be set with
IO#set_encoding or at IO object creation (see IO.new options).
The internal encoding is optional and when not set, the Ruby default internal encoding is used. If not explicitly set this default internal encoding is
nil meaning that by default, no transcoding occurs.
The default internal encoding can be set with the interpreter option
-E. Encoding.default_internal returns the current internal encoding.
$ ruby -e 'p Encoding.default_internal' nil $ ruby -E ISO-8859-1:UTF-8 -e "p [Encoding.default_external, \ Encoding.default_internal]" [#<Encoding:ISO-8859-1>, #<Encoding:UTF-8>]
The default internal encoding may also be set through Encoding.default_internal=, but you should not do this as strings created before and after the change will have inconsistent encodings. Instead use
ruby -E to invoke ruby with the correct internal encoding.
In the following example a UTF-8 encoded string “Ru00E9sumu00E9” is transcoded for output to ISO-8859-1 encoding, then read back in and transcoded to UTF-8:
string = "R\u00E9sum\u00E9" open("transcoded.txt", "w:ISO-8859-1") do |io| io.write(string) end puts "raw text:" p File.binread("transcoded.txt") puts open("transcoded.txt", "r:ISO-8859-1:UTF-8") do |io| puts "transcoded text:" p io.read end
While writing the file, the internal encoding is not specified as it is only necessary for reading. While reading the file both the internal and external encoding must be specified to obtain the correct result.
$ ruby t.rb raw text: "R\xE9sum\xE9" transcoded text: "R\u00E9sum\u00E9"