UTF-8/it

L'UTF-8 è una codifica dei caratteri a lunghezza variabile, il che significa per esempio che vengono utilizzati da 1 a 4 bytes per simbolo. Quindi, il primo byte UTF-8 è utilizzato per codificare caratteri ASCII, garantendo alla codifica piena compatibilità con il codice ASCII. Secondo UTF-8, ASCII e caratteri Latini sono intercambiabili con un piccolo incremento di dimensione dei dati, dato che solo il primo byte è utilizzato. Gli utilizzatori degli alfabeti orientali, come il Giapponese, che hanno assegnato un più ampio range, sono infelici, perchè questo porta ad una ridondanza fino al 50% nei loro dati

Cos'è la Codifica Caratteri?
I Computer non capiscono il testo di per sè. Al contrario, ogni carattere è rappresentato da un numero. In passato, ogni set di numeri utilizzato per rappresentare alfabeti e caratteri (noto come codice, codifica o set di caratteri) era limitato in dimensione per via dei limiti hardware.

The History of Character Encodings
The most common (or at least the most widely accepted) character set is ASCII (American Standard Code for Information Interchange). It is widely held that ASCII is the most successful software standard ever. Modern ASCII was standardised in 1986 (ANSI X3.4, RFC 20, ISO/IEC 646:1991, ECMA-6) by the American National Standards Institute.

ASCII is strictly seven-bit, meaning that it uses bit patterns representable with seven binary digits, which provides a range of 0 to 127 in decimal. These include 32 non-visible control characters, most between 0 and 31, with the final control character, DEL or delete at 127. Characters 32 to 126 are visible characters: a space, punctuation marks, Latin letters and numbers.

The eighth bit in ASCII was originally used as a parity bit for error checking. If this is not desired, it is left as 0. This means that, with ASCII, each character is represented by a single byte.

Although ASCII was enough for communication in modern English, in other European languages that include accented characters, things were not so easy. The ISO 8859 standards were developed to meet these needs. They were backwards compatible with ASCII, but instead of leaving the eighth bit blank, they used it to allow another 127 characters in each encoding. ISO 8859's limitations soon came to light, and there are currently 15 variants of the ISO 8859 standard (8859-1 through to 8859-15). Outside of the ASCII-compatible byte range of these character sets, there is often conflict between the letters represented by each byte. To complicate interoperability between character encodings further, Windows-1252 is used in some versions of Microsoft Windows instead for Western European languages. This is a superset of ISO 8859-1, however it is different in several ways. These sets do all retain ASCII compatibility, however.

The necessary development of completely different single-byte encodings for non-Latin alphabets, such as EUC (Extended Unix Coding) which is used for Japanese and Korean (and to a lesser extent Chinese) created more confusion, while other operating systems still used different character sets for the same languages, for example, Shift-JIS and ISO-2022-JP. Users wishing to view cyrillic glyphs had to choose between KOI8-R for Russian and Bulgarian or KOI8-U for Ukrainian, as well as all the other cyrillic encodings such as the unsuccessful ISO 8859-5, and the common Windows-1251 set. All of these character sets broke most compatibility with ASCII (although KOI8 encodings place cyrillic characters in Latin order, so in case the eighth bit is stripped, text is still decipherable on an ASCII terminal through case-reversed transliteration.)

This has led to confusion, and also to an almost total inability for multilingual communication, especially across different alphabets. Enter Unicode.

What is Unicode?
Unicode throws away the traditional single-byte limit of character sets. It uses 17 "planes" of 65,536 code points to describe a maximum of 1,114,112 characters. As the first plane, aka. "Basic Multilingual Plane" or BMP, contains almost everything you will ever use, many have made the wrong assumption that Unicode was a 16-bit character set.

Unicode has been mapped in many different ways, but the two most common are UTF (Unicode Transformation Format) and UCS (Universal Character Set). A number after UTF indicates the number of bits in one unit, while the number after UCS indicates the number of bytes. UTF-8 has become the most widespread means for the interchange of Unicode text as a result of its eight-bit clean nature, and it is the subject of this document.

What UTF-8 Can Do for You
UTF-8 allows you to work in a standards-compliant and internationally accepted multilingual environment, with a comparatively low data redundancy. UTF-8 is the preferred way for transmitting non-ASCII characters over the Internet, through Email, IRC or almost any other medium. Despite this, many people regard UTF-8 in online communication as abusive. It is always best to be aware of the attitude towards UTF-8 in a specific channel, mailing list or Usenet group before using non-ASCII UTF-8.

Finding or Creating UTF-8 Locales
Now that you understand the principles behind Unicode, you're ready to start using UTF-8 with your system.

The preliminary requirement for UTF-8 is to have a version of glibc installed that has national language support. The recommend means to do this is the file. It is beyond the scope of this document to explain the usage of this file though. It is explained in the Gentoo Localization Guide.

Next, we'll need to decide whether a UTF-8 locale is already available for our language, or whether we need to create one.

From the output of this command line, we need to take the result with a suffix similar to. If there is no result with a suffix similar to, we need to create a UTF-8 compatible locale.

Replace "en_GB" with your desired locale setting:

Another way to include a UTF-8 locale is to add it to the file and generate necessary locales with   command.

Line in /etc/locale.gen

Setting the Locale
There is one environment variable that needs to be set in order to use our new UTF-8 locales:  (or optionally  , if you want to change the system language as well). There are also many different ways to set it; some people prefer to only have a UTF-8 environment for a specific user, in which case they set them in their (if you use   ),  or  (if you use   ). More details and best practices can be found in our Localization Guide.

Others prefer to set the locale globally. One specific circumstance where the author particularly recommends doing this is when is in use, because this init script starts the display manager and desktop before any of the aforementioned shell startup files are sourced, and so before any of the variables are in the environment.

Setting the locale globally should be done using. The file should look something like the following:

Demonstration /etc/env.d/02locale

Next, the environment must be updated with the change.

Now, run  with no arguments to see if we have the correct variables in our environment:

That's everything. You are now using UTF-8 locales, and the next hurdle is the configuration of the applications you use from day to day.

Application Support
When Unicode first started gaining momentum in the software world, multibyte character sets were not well suited to languages like C, in which many of the day-to-day programs people use are written. Even today, some programs are not able to handle UTF-8 properly. Fortunately, most are!

Filenames, NTFS, and FAT
There are several NLS options in the Linux kernel configuration menu, but it is important to not become confused! For the most part, the only thing you need to do is to build UTF-8 NLS support into your kernel, and change the default NLS option to utf8.

If you plan on mounting NTFS partitions, you may need to specify an  option with mount. If you plan on mounting FAT partitions, you may need to specify a  option with mount. Optionally, you can also set a default codepage for FAT in the kernel configuration. Note that the  option with mount will override the kernel settings.

You should avoid setting  to UTF-8, as it is not recommended. Instead, you may want to pass the option utf8=true when mounting your FAT partitions. For further information, see  and the kernel documentation at.

For changing the encoding of filenames,  can be used.

The format of the  command is as follows:

Substitute iso-8859-1 with the charset you are converting from:

For changing the contents of files, use the  utility, bundled with. Substitute iso-8859-1 with the charset you are converting from, and check that the output is sane:

To convert a file, you must create another file:

can also be used for this purpose.

The System Console
To enable UTF-8 on the console, you should edit and set , and also read the comments in that file -- it is important to have a font that has a good range of characters if you plan on making the most of Unicode. For this to work, make sure you have properly created a Unicode locale.

The  variable, set in, should have a Unicode keymap specified.

Example /etc/conf.d/keymaps snippet

Ncurses and Slang
It is wise to add  to your global USE flags in, and then to remerge   and   if appropriate. Portage will do this automatically when you update your system:

We also need to rebuild packages that link to these, now the USE changes have been applied. The tool we use is part of the   package.

KDE, GNOME and Xfce
All of the major desktop environments have full Unicode support, and will require no further setup than what has already been covered in this guide. This is because the underlying graphical toolkits (Qt or GTK+2) are UTF-8 aware. Subsequently, all applications running on top of these toolkits should be UTF-8-aware out of the box.

The exceptions to this rule come in Xlib and GTK+1. GTK+1 requires a iso-10646-1 FontSpec in the ~/.gtkrc, for example. Also, applications using Xlib or Xaw will need to be given a similar FontSpec, otherwise they will not work.

Example ~/.gtkrc (for GTK+1) that defines a Unicode compatible font

If an application has support for both a Qt and GTK+2 GUI, the GTK+2 GUI will generally give better results with Unicode.

X11 and Fonts
TrueType fonts have support for Unicode, and most of the fonts that ship with Xorg have impressive character support, although, obviously, not every single glyph available in Unicode has been created for that font. To build fonts (including the Bitstream Vera set) with support for East Asian letters with X, make sure you have the  USE flag set. Many other applications utilise this flag, so it may be worthwhile to add it as a permanent USE flag.

Also, several font packages in Portage are Unicode aware.

Window Managers and Terminal Emulators
Window managers not built on GTK or Qt generally have very good Unicode support, as they often use the Xft library for handling fonts. If your window manager does not use Xft for fonts, you can still use the FontSpec mentioned in the previous section as a Unicode font.

Terminal emulators that use Xft and support Unicode are harder to come by. Aside from Konsole and gnome-terminal, the best options in Portage are ,   ,   ,   , or plain   when built with the   USE flag and invoked as. supports UTF-8 too, when invoked as  or the following is put into the  :

~/.screenrc for UTF-8

Vim, Emacs, Xemacs and Nano
Vim provides full UTF-8 support, and also has builtin detection of UTF-8 files. For further information in Vim, use.

GNU Emacs since version 23 and XEmacs version 21.5 have full UTF-8 support. GNU Emacs 24 also supports editing bidirectional text.

Nano has provided full UTF-8 support since version 1.3.6.

Shells
Currently,  provides full Unicode support through the GNU readline library. Z Shell offers Unicode support with the   USE flag.

The C shell,  and   do not provide UTF-8 support at all.

Irssi
Irssi has complete UTF-8 support, although it does require a user to set an option.

For channels where non-ASCII characters are often exchanged in non-UTF-8 charsets, the  command may be used to convert the characters. Type  for more information.

Mutt
The Mutt mail user agent has very good Unicode support. To use UTF-8 with Mutt, you don't need to put anything in your configuration files. Mutt will work under unicode enviroment without modification if all your configuration files (signature included) are UTF-8 encoded.

Further information is available from the Mutt Wiki.

Man
Man pages are an integral part of any Linux machine. To ensure that any unicode in your man pages render correctly, edit and replace a line as shown below.

man.conf changes for Unicode support

elinks and links
These are commonly used text-based browsers, and we shall see how we can enable UTF-8 support on them. On  and  , there are two ways to go about this, one using the Setup option from within the browser or editing the config file. To set the option through the browser, open a site with  or   and then   to enter the Setup Menu then select Terminal options, or press. Scroll down and select the last option  by pressing Enter. Then Save and exit the menu. On  you may have to do a repeat   and then press   to save. The config file option, is shown below.

Enabling UTF-8 for elinks/links

Samba
Samba is a software suite which implements the SMB (Server Message Block) protocol for UNIX systems such as Macs, Linux and FreeBSD. The protocol is also sometimes referred to as the Common Internet File System (CIFS). Samba also includes the NetBIOS system - used for file sharing over windows networks.

add the following under the [global] section:

Testing it all out
There are numerous UTF-8 test websites around. , ,   ,   and all Mozilla based browsers (including Firefox) support UTF-8. Konqueror and Opera have full UTF-8 support too.

When using one of the text-only web browsers, make absolutely sure you are using a Unicode-aware terminal.

If you see certain characters displayed as boxes with letters or numbers inside, this means that your font does not have a character for the symbol or glyph that the UTF-8 wants. Instead, it displays a box with the hex code of the UTF-8 symbol.


 * A W3C UTF-8 Test Page
 * A UTF-8 test page provided by the University of Frankfurt

Input Methods
Dead keys may be used to input characters in X that are not included on your keyboard. These work by pressing your right Alt key (or in some countries, AltGr) and an optional key from the non-alphabetical section of the keyboard to the left of the return key at once, releasing them, and then pressing a letter. The dead key should modify it. Input can be further modified by using the Shift key at the same time as pressing the AltGr and modifier.

To enable dead keys in X, you need a layout that supports it. Most European layouts already have dead keys with the default variant. However, this is not true of North American layouts. Although there is a degree of inconsistency between layouts, the easiest solution seems to be to use a layout in the form "en_US" rather than "us", for example. The layout is set in like so:

/etc/X11/xorg.conf snippet

This change will come into effect when your X server is restarted. To apply the change now, use the  tool, for example,.

It is probably easiest to describe dead keys with examples. Although the results are locale dependent, the concepts should remain the same regardless of locale. The examples contain UTF-8, so to view them you need to either tell your browser to view the page as UTF-8, or have a UTF-8 locale already configured.

When I press AltGr and [ at once, release them, and then press a, 'ä' is produced. When I press AltGr and [ at once, and then press e, 'ë' is produced. When I press AltGr and ; at once, 'á' is produced, and when I press AltGr and ; at once, release them, and then press e, 'é' is produced.

By pressing AltGr, Shift and [ at once, releasing them, and then pressing a, a Scandinavian 'å' is produced. Similarly, when I press AltGr, Shift and [ at once, release only the [, and then press it again, '°' is produced. Although it looks like one, this (U+02DA) is not the same as a degree symbol (U+00B0).

AltGr can be used with alphabetical keys alone. For example, AltGr and m, a Greek lower-case letter mu is produced. AltGr and s produce a scharfes s or esszet, etc. As many European users would expect (because it is marked on their keyboard), AltGr and 4 (or E depending on the keyboard layout) produces a Euro sign, '€'.

Resources

 * The Wikipedia entry for Unicode
 * The Wikipedia entry for UTF-8
 * Unicode.org
 * UTF-8.com
 * RFC 3629
 * RFC 2277
 * Characters vs. Bytes

System Configuration Files (in /etc)
Most system configuration files, such as, do not support UTF-8. It is recommended to stick with the ASCII character set for these files.

Acknowledgements
We would like to thank the following authors and editors for their contributions to this guide:


 * Thomas Martin
 * Alexander Simonov
 * Shyam Mani
 * nightmorph