Q. International Character Set Support
Emacs supports a wide variety of international character sets,
including European variants of the Latin alphabet, as well as Chinese,
Cyrillic, Devanagari (Hindi and Marathi), Ethiopic, Greek, Hebrew, IPA,
Japanese, Korean, Lao, Thai, Tibetan, and Vietnamese scripts. These features
have been merged from the modified version of Emacs known as MULE (for
"MULti-lingual Enhancement to GNU Emacs")
Emacs also supports various encodings of these characters used by
other internationalized software, such as word processors and mailers.
Emacs allows editing text with international characters by supporting
all the related activities:
-
You can visit files with non-ASCII characters, save non-ASCII text, and
pass non-ASCII text between Emacs and programs it invokes (such as
compilers, spell-checkers, and mailers). Setting your language
environment (see section Q.3 Language Environments) takes care of setting up the
coding systems and other options for a specific language or culture.
Alternatively, you can specify how Emacs should encode or decode text
for each command; see Q.9 Specifying a Coding System.
-
You can display non-ASCII characters encoded by the various scripts.
This works by using appropriate fonts on X and similar graphics
displays (see section Q.11 Defining fontsets), and by sending special codes to
text-only displays (see section Q.9 Specifying a Coding System). If some characters are
displayed incorrectly, refer to Q.12 Undisplayable Characters, which
describes possible problems and explains how to solve them.
-
You can insert non-ASCII characters or search for them. To do that,
you can specify an input method (see section Q.5 Selecting an Input Method) suitable
for your language, or use the default input method set up when you set
your language environment. (Emacs input methods are part of the Leim
package, which must be installed for you to be able to use them.) If
your keyboard can produce non-ASCII characters, you can select an
appropriate keyboard coding system (see section Q.9 Specifying a Coding System), and Emacs
will accept those characters. Latin-1 characters can also be input by
using the C-x 8 prefix, see C-x 8. On X Window systems, your locale should be set to an
appropriate value to make sure Emacs interprets keyboard input
correctly, see locales.
The rest of this chapter describes these issues in detail.
Q.1 Introduction to International Character Sets
The users of international character sets and scripts have established
many more-or-less standard coding systems for storing files. Emacs
internally uses a single multibyte character encoding, so that it can
intermix characters from all these scripts in a single buffer or string.
This encoding represents each non-ASCII character as a sequence of bytes
in the range 0200 through 0377. Emacs translates between the multibyte
character encoding and various other coding systems when reading and
writing files, when exchanging data with subprocesses, and (in some
cases) in the C-q command (see section Q.6 Unibyte and Multibyte Non-ASCII characters).
The command C-h h (view-hello-file) displays the file
`etc/HELLO', which shows how to say "hello" in many languages.
This illustrates various scripts. If some characters can't be
displayed on your terminal, they appear as `?' or as hollow boxes
(see section Q.12 Undisplayable Characters).
Keyboards, even in the countries where these character sets are used,
generally don't have keys for all the characters in them. So Emacs
supports various input methods, typically one for each script or
language, to make it convenient to type them.
The prefix key C-x RET is used for commands that pertain
to multibyte characters, coding systems, and input methods.
Q.2 Enabling Multibyte Characters
You can enable or disable multibyte character support, either for
Emacs as a whole, or for a single buffer. When multibyte characters are
disabled in a buffer, then each byte in that buffer represents a
character, even codes 0200 through 0377. The old features for
supporting the European character sets, ISO Latin-1 and ISO Latin-2,
work as they did in Emacs 19 and also work for the other ISO 8859
character sets.
However, there is no need to turn off multibyte character support to
use ISO Latin; the Emacs multibyte character set includes all the
characters in these character sets, and Emacs can translate
automatically to and from the ISO codes.
By default, Emacs starts in multibyte mode, because that allows you to
use all the supported languages and scripts without limitations.
To edit a particular file in unibyte representation, visit it using
find-file-literally. See section M.2 Visiting Files. To convert a buffer in
multibyte representation into a single-byte representation of the same
characters, the easiest way is to save the contents in a file, kill the
buffer, and find the file again with find-file-literally. You
can also use C-x RET c
(universal-coding-system-argument) and specify `raw-text' as
the coding system with which to find or save a file. See section Q.9 Specifying a Coding System. Finding a file as `raw-text' doesn't disable format
conversion, uncompression and auto mode selection as
find-file-literally does.
To turn off multibyte character support by default, start Emacs with
the `--unibyte' option (see section AE.2 Initial Options), or set the
environment variable EMACS_UNIBYTE. You can also customize
enable-multibyte-characters or, equivalently, directly set the
variable default-enable-multibyte-characters to nil in
your init file to have basically the same effect as `--unibyte'.
To convert a unibyte session to a multibyte session, set
default-enable-multibyte-characters to t. Buffers which
were created in the unibyte session before you turn on multibyte support
will stay unibyte. You can turn on multibyte support in a specific
buffer by invoking the command toggle-enable-multibyte-characters
in that buffer.
With `--unibyte', multibyte strings are not created during
initialization from the values of environment variables,
`/etc/passwd' entries etc. that contain non-ASCII 8-bit
characters.
Emacs normally loads Lisp files as multibyte, regardless of whether
you used `--unibyte'. This includes the Emacs initialization
file, `.emacs', and the initialization files of Emacs packages
such as Gnus. However, you can specify unibyte loading for a
particular Lisp file, by putting `-*-unibyte: t;-*-' in a
comment on the first line. Then that file is always loaded as unibyte
text, even if you did not start Emacs with `--unibyte'. The
motivation for these conventions is that it is more reliable to always
load any particular Lisp file in the same way. However, you can load
a Lisp file as unibyte, on any one occasion, by typing C-x
RET c raw-text RET immediately before loading it.
The mode line indicates whether multibyte character support is enabled
in the current buffer. If it is, there are two or more characters (most
often two dashes) before the colon near the beginning of the mode line.
When multibyte characters are not enabled, just one dash precedes the
colon.
Q.3 Language Environments
All supported character sets are supported in Emacs buffers whenever
multibyte characters are enabled; there is no need to select a
particular language in order to display its characters in an Emacs
buffer. However, it is important to select a language environment
in order to set various defaults. The language environment really
represents a choice of preferred script (more or less) rather than a
choice of language.
The language environment controls which coding systems to recognize
when reading text (see section Q.8 Recognizing Coding Systems). This applies to files,
incoming mail, netnews, and any other text you read into Emacs. It may
also specify the default coding system to use when you create a file.
Each language environment also specifies a default input method.
To select a language environment, customize the option
current-language-environment or use the command M-x
set-language-environment. It makes no difference which buffer is
current when you use this command, because the effects apply globally to
the Emacs session. The supported language environments include:
Chinese-BIG5, Chinese-CNS, Chinese-GB, Cyrillic-ALT, Cyrillic-ISO,
Cyrillic-KOI8, Czech, Devanagari, Dutch, English, Ethiopic, German,
Greek, Hebrew, IPA, Japanese, Korean, Lao, Latin-1, Latin-2, Latin-3,
Latin-4, Latin-5, Latin-8 (Celtic), Latin-9 (updated Latin-1, with the
Euro sign), Polish, Romanian, Slovak, Slovenian, Spanish, Thai,
Tibetan, Turkish, and Vietnamese.
To display the script(s) used by your language environment on a
graphical display, you need to have a suitable font. If some of the
characters appear as empty boxes, you should install the GNU Intlfonts
package, which includes fonts for all supported scripts.(4)
See section Q.10 Fontsets, for more details about setting up your fonts.
Some operating systems let you specify the character-set locale you
are using by setting the locale environment variables LC_ALL,
LC_CTYPE, or LANG.(5) During startup, Emacs looks up your character-set locale's
name in the system locale alias table, matches its canonical name
against entries in the value of the variables
locale-charset-language-names and locale-language-names,
and selects the corresponding language environment if a match is found.
(The former variable overrides the latter.) It also adjusts the display
table and terminal coding system, the locale coding system, the
preferred coding system as needed for the locale, and--last but not
least--the way Emacs decodes non-ASCII characters sent by your keyboard.
If you modify the LC_ALL, LC_CTYPE, or LANG
environment variables while running Emacs, you may want to invoke the
set-locale-environment function afterwards to readjust the
language environment from the new locale.
The set-locale-environment function normally uses the preferred
coding system established by the language environment to decode system
messages. But if your locale matches an entry in the variable
locale-preferred-coding-systems, Emacs uses the corresponding
coding system instead. For example, if the locale `ja_JP.PCK'
matches japanese-shift-jis in
locale-preferred-coding-systems, Emacs uses that encoding even
though it might normally use japanese-iso-8bit.
You can override the language environment chosen at startup with
explicit use of the command set-language-environment, or with
customization of current-language-environment in your init
file.
To display information about the effects of a certain language
environment lang-env, use the command C-h L lang-env
RET (describe-language-environment). This tells you which
languages this language environment is useful for, and lists the
character sets, coding systems, and input methods that go with it. It
also shows some sample text to illustrate scripts used in this language
environment. By default, this command describes the chosen language
environment.
You can customize any language environment with the normal hook
set-language-environment-hook. The command
set-language-environment runs that hook after setting up the new
language environment. The hook functions can test for a specific
language environment by checking the variable
current-language-environment. This hook is where you should
put non-default settings for specific language environment, such as
coding systems for keyboard input and terminal output, the default
input method, etc.
Before it starts to set up the new language environment,
set-language-environment first runs the hook
exit-language-environment-hook. This hook is useful for undoing
customizations that were made with set-language-environment-hook.
For instance, if you set up a special key binding in a specific language
environment using set-language-environment-hook, you should set
up exit-language-environment-hook to restore the normal binding
for that key.
Q.4 Input Methods
An input method is a kind of character conversion designed
specifically for interactive input. In Emacs, typically each language
has its own input method; sometimes several languages which use the same
characters can share one input method. A few languages support several
input methods.
The simplest kind of input method works by mapping ASCII letters
into another alphabet; this allows you to use one other alphabet
instead of ASCII. The Greek and Russian input methods
work this way.
A more powerful technique is composition: converting sequences of
characters into one letter. Many European input methods use composition
to produce a single non-ASCII letter from a sequence that consists of a
letter followed by accent characters (or vice versa). For example, some
methods convert the sequence a' into a single accented letter.
These input methods have no special commands of their own; all they do
is compose sequences of printing characters.
The input methods for syllabic scripts typically use mapping followed
by composition. The input methods for Thai and Korean work this way.
First, letters are mapped into symbols for particular sounds or tone
marks; then, sequences of these which make up a whole syllable are
mapped into one syllable sign.
Chinese and Japanese require more complex methods. In Chinese input
methods, first you enter the phonetic spelling of a Chinese word (in
input method chinese-py, among others), or a sequence of
portions of the character (input methods chinese-4corner and
chinese-sw, and others). One input sequence typically
corresponds to many possible Chinese characters. You select the one
you mean using keys such as C-f, C-b, C-n,
C-p, and digits, which have special meanings in this situation.
The possible characters are conceptually arranged in several rows,
with each row holding up to 10 alternatives. Normally, Emacs displays
just one row at a time, in the echo area; (i/j)
appears at the beginning, to indicate that this is the ith row
out of a total of j rows. Type C-n or C-p to
display the next row or the previous row.
Type C-f and C-b to move forward and backward among
the alternatives in the current row. As you do this, Emacs highlights
the current alternative with a special color; type C-SPC
to select the current alternative and use it as input. The
alternatives in the row are also numbered; the number appears before
the alternative. Typing a digit n selects the nth
alternative of the current row and uses it as input.
TAB in these Chinese input methods displays a buffer showing
all the possible characters at once; then clicking Mouse-2 on
one of them selects that alternative. The keys C-f, C-b,
C-n, C-p, and digits continue to work as usual, but they
do the highlighting in the buffer showing the possible characters,
rather than in the echo area.
In Japanese input methods, first you input a whole word using
phonetic spelling; then, after the word is in the buffer, Emacs
converts it into one or more characters using a large dictionary. One
phonetic spelling corresponds to a number of different Japanese words;
to select one of them, use C-n and C-p to cycle through
the alternatives.
Sometimes it is useful to cut off input method processing so that the
characters you have just entered will not combine with subsequent
characters. For example, in input method latin-1-postfix, the
sequence e ' combines to form an `e' with an accent. What if
you want to enter them as separate characters?
One way is to type the accent twice; this is a special feature for
entering the separate letter and accent. For example, e ' ' gives
you the two characters `e''. Another way is to type another letter
after the e---something that won't combine with that--and
immediately delete it. For example, you could type e e DEL
' to get separate `e' and `''.
Another method, more general but not quite as easy to type, is to use
C-\ C-\ between two characters to stop them from combining. This
is the command C-\ (toggle-input-method) used twice.
See section Q.5 Selecting an Input Method.
C-\ C-\ is especially useful inside an incremental search,
because it stops waiting for more characters to combine, and starts
searching for what you have already entered.
The variables input-method-highlight-flag and
input-method-verbose-flag control how input methods explain
what is happening. If input-method-highlight-flag is
non-nil, the partial sequence is highlighted in the buffer (for
most input methods--some disable this feature). If
input-method-verbose-flag is non-nil, the list of
possible characters to type next is displayed in the echo area (but
not when you are in the minibuffer).
Input methods are implemented in the separate Leim package: they are
available only if the system administrator used Leim when building
Emacs. If Emacs was built without Leim, you will find that no input
methods are defined.
Q.5 Selecting an Input Method
- C-\
- Enable or disable use of the selected input method.
- C-x RET C-\ method RET
- Select a new input method for the current buffer.
- C-h I method RET
- C-h C-\ method RET
-
Describe the input method method (
describe-input-method).
By default, it describes the current input method (if any). This
description should give you the full details of how to use any
particular input method.
- M-x list-input-methods
- Display a list of all the supported input methods.
To choose an input method for the current buffer, use C-x
RET C-\ (set-input-method). This command reads the
input method name from the minibuffer; the name normally starts with the
language environment that it is meant to be used with. The variable
current-input-method records which input method is selected.
Input methods use various sequences of ASCII characters to stand for
non-ASCII characters. Sometimes it is useful to turn off the input
method temporarily. To do this, type C-\
(toggle-input-method). To reenable the input method, type
C-\ again.
If you type C-\ and you have not yet selected an input method,
it prompts for you to specify one. This has the same effect as using
C-x RET C-\ to specify an input method.
When invoked with a numeric argument, as in C-u C-\,
toggle-input-method always prompts you for an input method,
suggesting the most recently selected one as the default.
Selecting a language environment specifies a default input method for
use in various buffers. When you have a default input method, you can
select it in the current buffer by typing C-\. The variable
default-input-method specifies the default input method
(nil means there is none).
In some language environments, which support several different input
methods, you might want to use an input method different from the
default chosen by set-language-environment. You can instruct
Emacs to select a different default input method for a certain
language environment, if you wish, by using
set-language-environment-hook (see section set-language-environment-hook). For example:
| | (defun my-chinese-setup ()
"Set up my private Chinese environment."
(if (equal current-language-environment "Chinese-GB")
(setq default-input-method "chinese-tonepy")))
(add-hook 'set-language-environment-hook 'my-chinese-setup)
|
This sets the default input method to be chinese-tonepy
whenever you choose a Chinese-GB language environment.
Some input methods for alphabetic scripts work by (in effect)
remapping the keyboard to emulate various keyboard layouts commonly used
for those scripts. How to do this remapping properly depends on your
actual keyboard layout. To specify which layout your keyboard has, use
the command M-x quail-set-keyboard-layout.
To display a list of all the supported input methods, type M-x
list-input-methods. The list gives information about each input
method, including the string that stands for it in the mode line.
Q.6 Unibyte and Multibyte Non-ASCII characters
When multibyte characters are enabled, character codes 0240 (octal)
through 0377 (octal) are not really legitimate in the buffer. The valid
non-ASCII printing characters have codes that start from 0400.
If you type a self-inserting character in the range 0240 through
0377, or if you use C-q to insert one, Emacs assumes you
intended to use one of the ISO Latin-n character sets, and
converts it to the Emacs code representing that Latin-n
character. You select which ISO Latin character set to use
through your choice of language environment
(see section Q.3 Language Environments).
If you do not specify a choice, the default is Latin-1.
If you insert a character in the range 0200 through 0237, which
forms the eight-bit-control character set, it is inserted
literally. You should normally avoid doing this since buffers
containing such characters have to be written out in either the
emacs-mule or raw-text coding system, which is usually
not what you want.
Q.7 Coding Systems
Users of various languages have established many more-or-less standard
coding systems for representing them. Emacs does not use these coding
systems internally; instead, it converts from various coding systems to
its own system when reading data, and converts the internal coding
system to other coding systems when writing data. Conversion is
possible in reading or writing files, in sending or receiving from the
terminal, and in exchanging data with subprocesses.
Emacs assigns a name to each coding system. Most coding systems are
used for one language, and the name of the coding system starts with the
language name. Some coding systems are used for several languages;
their names usually start with `iso'. There are also special
coding systems no-conversion, raw-text and
emacs-mule which do not convert printing characters at all.
A special class of coding systems, collectively known as
codepages, is designed to support text encoded by MS-Windows and
MS-DOS software. To use any of these systems, you need to create it
with M-x codepage-setup. See section AH.6 International Support on MS-DOS. After
creating the coding system for the codepage, you can use it as any
other coding system. For example, to visit a file encoded in codepage
850, type C-x RET c cp850 RET C-x C-f filename
RET.
In addition to converting various representations of non-ASCII
characters, a coding system can perform end-of-line conversion. Emacs
handles three different conventions for how to separate lines in a file:
newline, carriage-return linefeed, and just carriage-return.
- C-h C coding RET
- Describe coding system coding.
- C-h C RET
- Describe the coding systems currently in use.
- M-x list-coding-systems
- Display a list of all the supported coding systems.
The command C-h C (describe-coding-system) displays
information about particular coding systems. You can specify a coding
system name as the argument; alternatively, with an empty argument, it
describes the coding systems currently selected for various purposes,
both in the current buffer and as the defaults, and the priority list
for recognizing coding systems (see section Q.8 Recognizing Coding Systems).
To display a list of all the supported coding systems, type M-x
list-coding-systems. The list gives information about each coding
system, including the letter that stands for it in the mode line
(see section B.3 The Mode Line).
Each of the coding systems that appear in this list--except for
no-conversion, which means no conversion of any kind--specifies
how and whether to convert printing characters, but leaves the choice of
end-of-line conversion to be decided based on the contents of each file.
For example, if the file appears to use the sequence carriage-return
linefeed to separate lines, DOS end-of-line conversion will be used.
Each of the listed coding systems has three variants which specify
exactly what to do for end-of-line conversion:
...-unix
- Don't do any end-of-line conversion; assume the file uses
newline to separate lines. (This is the convention normally used
on Unix and GNU systems.)
...-dos
- Assume the file uses carriage-return linefeed to separate lines, and do
the appropriate conversion. (This is the convention normally used on
Microsoft systems.(6))
...-mac
- Assume the file uses carriage-return to separate lines, and do the
appropriate conversion. (This is the convention normally used on the
Macintosh system.)
These variant coding systems are omitted from the
list-coding-systems display for brevity, since they are entirely
predictable. For example, the coding system iso-latin-1 has
variants iso-latin-1-unix, iso-latin-1-dos and
iso-latin-1-mac.
The coding system raw-text is good for a file which is mainly
ASCII text, but may contain byte values above 127 which are not meant to
encode non-ASCII characters. With raw-text, Emacs copies those
byte values unchanged, and sets enable-multibyte-characters to
nil in the current buffer so that they will be interpreted
properly. raw-text handles end-of-line conversion in the usual
way, based on the data encountered, and has the usual three variants to
specify the kind of end-of-line conversion to use.
In contrast, the coding system no-conversion specifies no
character code conversion at all--none for non-ASCII byte values and
none for end of line. This is useful for reading or writing binary
files, tar files, and other files that must be examined verbatim. It,
too, sets enable-multibyte-characters to nil.
The easiest way to edit a file with no conversion of any kind is with
the M-x find-file-literally command. This uses
no-conversion, and also suppresses other Emacs features that
might convert the file contents before you see them. See section M.2 Visiting Files.
The coding system emacs-mule means that the file contains
non-ASCII characters stored with the internal Emacs encoding. It
handles end-of-line conversion based on the data encountered, and has
the usual three variants to specify the kind of end-of-line conversion.
Q.8 Recognizing Coding Systems
Emacs tries to recognize which coding system to use for a given text
as an integral part of reading that text. (This applies to files
being read, output from subprocesses, text from X selections, etc.)
Emacs can select the right coding system automatically most of the
time--once you have specified your preferences.
Some coding systems can be recognized or distinguished by which byte
sequences appear in the data. However, there are coding systems that
cannot be distinguished, not even potentially. For example, there is no
way to distinguish between Latin-1 and Latin-2; they use the same byte
values with different meanings.
Emacs handles this situation by means of a priority list of coding
systems. Whenever Emacs reads a file, if you do not specify the coding
system to use, Emacs checks the data against each coding system,
starting with the first in priority and working down the list, until it
finds a coding system that fits the data. Then it converts the file
contents assuming that they are represented in this coding system.
The priority list of coding systems depends on the selected language
environment (see section Q.3 Language Environments). For example, if you use
French, you probably want Emacs to prefer Latin-1 to Latin-2; if you use
Czech, you probably want Latin-2 to be preferred. This is one of the
reasons to specify a language environment.
However, you can alter the priority list in detail with the command
M-x prefer-coding-system. This command reads the name of a coding
system from the minibuffer, and adds it to the front of the priority
list, so that it is preferred to all others. If you use this command
several times, each use adds one element to the front of the priority
list.
If you use a coding system that specifies the end-of-line conversion
type, such as iso-8859-1-dos, what this means is that Emacs
should attempt to recognize iso-8859-1 with priority, and should
use DOS end-of-line conversion when it does recognize iso-8859-1.
Sometimes a file name indicates which coding system to use for the
file. The variable file-coding-system-alist specifies this
correspondence. There is a special function
modify-coding-system-alist for adding elements to this list. For
example, to read and write all `.txt' files using the coding system
china-iso-8bit, you can execute this Lisp expression:
| | (modify-coding-system-alist 'file "\\.txt\\'" 'china-iso-8bit)
|
The first argument should be file, the second argument should be
a regular expression that determines which files this applies to, and
the third argument says which coding system to use for these files.
Emacs recognizes which kind of end-of-line conversion to use based on
the contents of the file: if it sees only carriage-returns, or only
carriage-return linefeed sequences, then it chooses the end-of-line
conversion accordingly. You can inhibit the automatic use of
end-of-line conversion by setting the variable inhibit-eol-conversion
to non-nil. If you do that, DOS-style files will be displayed
with the `^M' characters visible in the buffer; some people
prefer this to the more subtle `(DOS)' end-of-line type
indication near the left edge of the mode line (see section eol-mnemonic).
By default, the automatic detection of coding system is sensitive to
escape sequences. If Emacs sees a sequence of characters that begin
with an escape character, and the sequence is valid as an ISO-2022
code, that tells Emacs to use one of the ISO-2022 encodings to decode
the file.
However, there may be cases that you want to read escape sequences
in a file as is. In such a case, you can set the variable
inhibit-iso-escape-detection to non-nil. Then the code
detection ignores any escape sequences, and never uses an ISO-2022
encoding. The result is that all escape sequences become visible in
the buffer.
The default value of inhibit-iso-escape-detection is
nil. We recommend that you not change it permanently, only for
one specific operation. That's because many Emacs Lisp source files
in the Emacs distribution contain non-ASCII characters encoded in the
coding system iso-2022-7bit, and they won't be
decoded correctly when you visit those files if you suppress the
escape sequence detection.
You can specify the coding system for a particular file using the
`-*-...-*-' construct at the beginning of a file, or a
local variables list at the end (see section AD.2.5 Local Variables in Files). You do this
by defining a value for the "variable" named coding. Emacs
does not really have a variable coding; instead of setting a
variable, this uses the specified coding system for the file. For
example, `-*-mode: C; coding: latin-1;-*-' specifies use of the
Latin-1 coding system, as well as C mode. When you specify the coding
explicitly in the file, that overrides
file-coding-system-alist.
The variables auto-coding-alist and
auto-coding-regexp-alist are the strongest way to specify the
coding system for certain patterns of file names, or for files
containing certain patterns; these variables even override
`-*-coding:-*-' tags in the file itself. Emacs uses
auto-coding-alist for tar and archive files, to prevent it
from being confused by a `-*-coding:-*-' tag in a member of the
archive and thinking it applies to the archive file as a whole.
Likewise, Emacs uses auto-coding-regexp-alist to ensure that
RMAIL files, whose names in general don't match any particular pattern,
are decoded correctly.
If Emacs recognizes the encoding of a file incorrectly, you can
reread the file using the correct coding system by typing C-x
RET c coding-system RET M-x revert-buffer
RET. To see what coding system Emacs actually used to decode
the file, look at the coding system mnemonic letter near the left edge
of the mode line (see section B.3 The Mode Line), or type C-h C RET.
Once Emacs has chosen a coding system for a buffer, it stores that
coding system in buffer-file-coding-system and uses that coding
system, by default, for operations that write from this buffer into a
file. This includes the commands save-buffer and
write-region. If you want to write files from this buffer using
a different coding system, you can specify a different coding system for
the buffer using set-buffer-file-coding-system (see section Q.9 Specifying a Coding System).
You can insert any possible character into any Emacs buffer, but
most coding systems can only handle some of the possible characters.
This means that it is possible for you to insert characters that
cannot be encoded with the coding system that will be used to save the
buffer. For example, you could start with an ASCII file and insert a
few Latin-1 characters into it, or you could edit a text file in
Polish encoded in iso-8859-2 and add some Russian words to it.
When you save the buffer, Emacs cannot use the current value of
buffer-file-coding-system, because the characters you added
cannot be encoded by that coding system.
When that happens, Emacs tries the most-preferred coding system (set
by M-x prefer-coding-system or M-x
set-language-environment), and if that coding system can safely
encode all of the characters in the buffer, Emacs uses it, and stores
its value in buffer-file-coding-system. Otherwise, Emacs
displays a list of coding systems suitable for encoding the buffer's
contents, and asks you to choose one of those coding systems.
If you insert the unsuitable characters in a mail message, Emacs
behaves a bit differently. It additionally checks whether the
most-preferred coding system is recommended for use in MIME messages;
if not, Emacs tells you that the most-preferred coding system is
not recommended and prompts you for another coding system. This is so
you won't inadvertently send a message encoded in a way that your
recipient's mail software will have difficulty decoding. (If you do
want to use the most-preferred coding system, you can still type its
name in response to the question.)
When you send a message with Mail mode (see section Z. Sending Mail), Emacs has
four different ways to determine the coding system to use for encoding
the message text. It tries the buffer's own value of
buffer-file-coding-system, if that is non-nil. Otherwise,
it uses the value of sendmail-coding-system, if that is
non-nil. The third way is to use the default coding system for
new files, which is controlled by your choice of language environment,
if that is non-nil. If all of these three values are nil,
Emacs encodes outgoing mail using the Latin-1 coding system.
When you get new mail in Rmail, each message is translated
automatically from the coding system it is written in, as if it were a
separate file. This uses the priority list of coding systems that you
have specified. If a MIME message specifies a character set, Rmail
obeys that specification, unless rmail-decode-mime-charset is
nil.
For reading and saving Rmail files themselves, Emacs uses the coding
system specified by the variable rmail-file-coding-system. The
default value is nil, which means that Rmail files are not
translated (they are read and written in the Emacs internal character
code).
Q.9 Specifying a Coding System
In cases where Emacs does not automatically choose the right coding
system, you can use these commands to specify one:
- C-x RET f coding RET
- Use coding system coding for the visited file
in the current buffer.
- C-x RET c coding RET
- Specify coding system coding for the immediately following
command.
- C-x RET k coding RET
- Use coding system coding for keyboard input.
- C-x RET t coding RET
- Use coding system coding for terminal output.
- C-x RET p input-coding RET output-coding RET
- Use coding systems input-coding and output-coding for
subprocess input and output in the current buffer.
- C-x RET x coding RET
- Use coding system coding for transferring selections to and from
other programs through the window system.
- C-x RET X coding RET
- Use coding system coding for transferring one
selection--the next one--to or from the window system.
The command C-x RET f (set-buffer-file-coding-system)
specifies the file coding system for the current buffer--in other
words, which coding system to use when saving or rereading the visited
file. You specify which coding system using the minibuffer. Since this
command applies to a file you have already visited, it affects only the
way the file is saved.
Another way to specify the coding system for a file is when you visit
the file. First use the command C-x RET c
(universal-coding-system-argument); this command uses the
minibuffer to read a coding system name. After you exit the minibuffer,
the specified coding system is used for the immediately following
command.
So if the immediately following command is C-x C-f, for example,
it reads the file using that coding system (and records the coding
system for when the file is saved). Or if the immediately following
command is C-x C-w, it writes the file using that coding system.
Other file commands affected by a specified coding system include
C-x C-i and C-x C-v, as well as the other-window variants of
C-x C-f.
C-x RET c also affects commands that start subprocesses,
including M-x shell (see section AC.15 Running Shell Commands from Emacs).
However, if the immediately following command does not use the coding
system, then C-x RET c ultimately has no effect.
An easy way to visit a file with no conversion is with the M-x
find-file-literally command. See section M.2 Visiting Files.
The variable default-buffer-file-coding-system specifies the
choice of coding system to use when you create a new file. It applies
when you find a new file, and when you create a buffer and then save it
in a file. Selecting a language environment typically sets this
variable to a good choice of default coding system for that language
environment.
The command C-x RET t (set-terminal-coding-system)
specifies the coding system for terminal output. If you specify a
character code for terminal output, all characters output to the
terminal are translated into that coding system.
This feature is useful for certain character-only terminals built to
support specific languages or character sets--for example, European
terminals that support one of the ISO Latin character sets. You need to
specify the terminal coding system when using multibyte text, so that
Emacs knows which characters the terminal can actually handle.
By default, output to the terminal is not translated at all, unless
Emacs can deduce the proper coding system from your terminal type or
your locale specification (see section Q.3 Language Environments).
The command C-x RET k (set-keyboard-coding-system)
or the Custom option keyboard-coding-system
specifies the coding system for keyboard input. Character-code
translation of keyboard input is useful for terminals with keys that
send non-ASCII graphic characters--for example, some terminals designed
for ISO Latin-1 or subsets of it.
By default, keyboard input is not translated at all.
There is a similarity between using a coding system translation for
keyboard input, and using an input method: both define sequences of
keyboard input that translate into single characters. However, input
methods are designed to be convenient for interactive use by humans, and
the sequences that are translated are typically sequences of ASCII
printing characters. Coding systems typically translate sequences of
non-graphic characters.
The command C-x RET x (set-selection-coding-system)
specifies the coding system for sending selected text to the window
system, and for receiving the text of selections made in other
applications. This command applies to all subsequent selections, until
you override it by using the command again. The command C-x
RET X (set-next-selection-coding-system) specifies the
coding system for the next selection made in Emacs or read by Emacs.
The command C-x RET p (set-buffer-process-coding-system)
specifies the coding system for input and output to a subprocess. This
command applies to the current buffer; normally, each subprocess has its
own buffer, and thus you can use this command to specify translation to
and from a particular subprocess by giving the command in the
corresponding buffer.
The default for translation of process input and output depends on the
current language environment.
The variable file-name-coding-system specifies a coding system
to use for encoding file names. If you set the variable to a coding
system name (as a Lisp symbol or a string), Emacs encodes file names
using that coding system for all file operations. This makes it
possible to use non-ASCII characters in file names--or, at least, those
non-ASCII characters which the specified coding system can encode.
If file-name-coding-system is nil, Emacs uses a default
coding system determined by the selected language environment. In the
default language environment, any non-ASCII characters in file names are
not encoded specially; they appear in the file system using the internal
Emacs representation.
Warning: if you change file-name-coding-system (or the
language environment) in the middle of an Emacs session, problems can
result if you have already visited files whose names were encoded using
the earlier coding system and cannot be encoded (or are encoded
differently) under the new coding system. If you try to save one of
these buffers under the visited file name, saving may use the wrong file
name, or it may get an error. If such a problem happens, use C-x
C-w to specify a new file name for that buffer.
The variable locale-coding-system specifies a coding system
to use when encoding and decoding system strings such as system error
messages and format-time-string formats and time stamps. That
coding system is also used for decoding non-ASCII keyboard input on X
Window systems. You should choose a coding system that is compatible
with the underlying system's text representation, which is normally
specified by one of the environment variables LC_ALL,
LC_CTYPE, and LANG. (The first one, in the order
specified above, whose value is nonempty is the one that determines
the text representation.)
Q.10 Fontsets
A font for X typically defines shapes for a single alphabet or script.
Therefore, displaying the entire range of scripts that Emacs supports
requires a collection of many fonts. In Emacs, such a collection is
called a fontset. A fontset is defined by a list of fonts, each
assigned to handle a range of character codes.
Each fontset has a name, like a font. The available X fonts are
defined by the X server; fontsets, however, are defined within Emacs
itself. Once you have defined a fontset, you can use it within Emacs by
specifying its name, anywhere that you could use a single font. Of
course, Emacs fontsets can use only the fonts that the X server
supports; if certain characters appear on the screen as hollow boxes,
this means that the fontset in use for them has no font for those
characters.(7)
Emacs creates two fontsets automatically: the standard fontset
and the startup fontset. The standard fontset is most likely to
have fonts for a wide variety of non-ASCII characters; however, this is
not the default for Emacs to use. (By default, Emacs tries to find a
font that has bold and italic variants.) You can specify use of the
standard fontset with the `-fn' option, or with the `Font' X
resource (see section AE.7 Font Specification Options). For example,
| | emacs -fn fontset-standard
|
A fontset does not necessarily specify a font for every character
code. If a fontset specifies no font for a certain character, or if it
specifies a font that does not exist on your system, then it cannot
display that character properly. It will display that character as an
empty box instead.
The fontset height and width are determined by the ASCII characters
(that is, by the font used for ASCII characters in that fontset). If
another font in the fontset has a different height, or a different
width, then characters assigned to that font are clipped to the
fontset's size. If highlight-wrong-size-font is non-nil,
a box is displayed around these wrong-size characters as well.
Q.11 Defining fontsets
Emacs creates a standard fontset automatically according to the value
of standard-fontset-spec. This fontset's name is
| | -*-fixed-medium-r-normal-*-16-*-*-*-*-*-fontset-standard
|
or just `fontset-standard' for short.
Bold, italic, and bold-italic variants of the standard fontset are
created automatically. Their names have `bold' instead of
`medium', or `i' instead of `r', or both.
If you specify a default ASCII font with the `Font' resource or
the `-fn' argument, Emacs generates a fontset from it
automatically. This is the startup fontset and its name is
fontset-startup. It does this by replacing the foundry,
family, add_style, and average_width fields of the
font name with `*', replacing charset_registry field with
`fontset', and replacing charset_encoding field with
`startup', then using the resulting string to specify a fontset.
For instance, if you start Emacs this way,
| | emacs -fn "*courier-medium-r-normal--14-140-*-iso8859-1"
|
Emacs generates the following fontset and uses it for the initial X
window frame:
| | -*-*-medium-r-normal-*-14-140-*-*-*-*-fontset-startup
|
With the X resource `Emacs.Font', you can specify a fontset name
just like an actual font name. But be careful not to specify a fontset
name in a wildcard resource like `Emacs*Font'---that wildcard
specification matches various other resources, such as for menus, and
menus cannot handle fontsets.
You can specify additional fontsets using X resources named
`Fontset-n', where n is an integer starting from 0.
The resource value should have this form:
| | fontpattern, [charsetname:fontname]...
|
fontpattern should have the form of a standard X font name, except
for the last two fields. They should have the form
`fontset-alias'.
The fontset has two names, one long and one short. The long name is
fontpattern. The short name is `fontset-alias'. You
can refer to the fontset by either name.
The construct `charset:font' specifies which font to
use (in this fontset) for one particular character set. Here,
charset is the name of a character set, and font is the
font to use for that character set. You can use this construct any
number of times in defining one fontset.
For the other character sets, Emacs chooses a font based on
fontpattern. It replaces `fontset-alias' with values
that describe the character set. For the ASCII character font,
`fontset-alias' is replaced with `ISO8859-1'.
In addition, when several consecutive fields are wildcards, Emacs
collapses them into a single wildcard. This is to prevent use of
auto-scaled fonts. Fonts made by scaling larger fonts are not usable
for editing, and scaling a smaller font is not useful because it is
better to use the smaller font in its own size, which is what Emacs
does.
Thus if fontpattern is this,
| | -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24
|
the font specification for ASCII characters would be this:
| | -*-fixed-medium-r-normal-*-24-*-ISO8859-1
|
and the font specification for Chinese GB2312 characters would be this:
| | -*-fixed-medium-r-normal-*-24-*-gb2312*-*
|
You may not have any Chinese font matching the above font
specification. Most X distributions include only Chinese fonts that
have `song ti' or `fangsong ti' in family field. In
such a case, `Fontset-n' can be specified as below:
| | Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\
chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-*
|
Then, the font specifications for all but Chinese GB2312 characters have
`fixed' in the family field, and the font specification for
Chinese GB2312 characters has a wild card `*' in the family
field.
The function that processes the fontset resource value to create the
fontset is called create-fontset-from-fontset-spec. You can also
call this function explicitly to create a fontset.
See section AE.7 Font Specification Options, for more information about font naming in X.
Q.12 Undisplayable Characters
Your terminal may be unable to display some non-ASCII
characters. Most non-windowing terminals can only use a single
character set (use the variable default-terminal-coding-system
(see section Q.9 Specifying a Coding System) to tell Emacs which one); characters which
can't be encoded in that coding system are displayed as `?' by
default.
Windowing terminals can display a broader range of characters, but
you may not have fonts installed for all of them; characters that have
no font appear as a hollow box.
If you use Latin-1 characters but your terminal can't display
Latin-1, you can arrange to display mnemonic ASCII sequences
instead, e.g. `"o' for o-umlaut. Load the library
`iso-ascii' to do this.
If your terminal can display Latin-1, you can display characters
from other European character sets using a mixture of equivalent
Latin-1 characters and ASCII mnemonics. Use the Custom option
latin1-display to enable this. The mnemonic ASCII
sequences mostly correspond to those of the prefix input methods.
Q.13 Single-byte Character Set Support
The ISO 8859 Latin-n character sets define character codes in
the range 0240 to 0377 octal (160 to 255 decimal) to handle the
accented letters and punctuation needed by various European languages
(and some non-European ones). If you disable multibyte characters,
Emacs can still handle one of these character codes at a time.
To specify which of these codes to use, invoke M-x
set-language-environment and specify a suitable language environment
such as `Latin-n'.
For more information about unibyte operation, see Q.2 Enabling Multibyte Characters. Note particularly that you probably want to ensure that
your initialization files are read as unibyte if they contain non-ASCII
characters.
Emacs can also display those characters, provided the terminal or font
in use supports them. This works automatically. Alternatively, if you
are using a window system, Emacs can also display single-byte characters
through fontsets, in effect by displaying the equivalent multibyte
characters according to the current language environment. To request
this, set the variable unibyte-display-via-language-environment
to a non-nil value.
If your terminal does not support display of the Latin-1 character
set, Emacs can display these characters as ASCII sequences which at
least give you a clear idea of what the characters are. To do this,
load the library iso-ascii. Similar libraries for other
Latin-n character sets could be implemented, but we don't have
them yet.
Normally non-ISO-8859 characters (decimal codes between 128 and 159
inclusive) are displayed as octal escapes. You can change this for
non-standard "extended" versions of ISO-8859 character sets by using the
function standard-display-8bit in the disp-table library.
There are several ways you can input single-byte non-ASCII
characters:
-
If your keyboard can generate character codes 128 (decimal) and up,
representing non-ASCII characters, you can type those character codes
directly.
On a windowing terminal, you should not need to do anything special to
use these keys; they should simply work. On a text-only terminal, you
should use the command M-x set-keyboard-coding-system or the
Custom option keyboard-coding-system to specify which coding
system your keyboard uses (see section Q.9 Specifying a Coding System). Enabling this
feature will probably require you to use ESC to type Meta
characters; however, on a Linux console or in xterm, you can
arrange for Meta to be converted to ESC and still be able type
8-bit characters present directly on the keyboard or using
Compose or AltGr keys. See section B.5 Kinds of User Input.
-
You can use an input method for the selected language environment.
See section Q.4 Input Methods. When you use an input method in a unibyte buffer,
the non-ASCII character you specify with it is converted to unibyte.
-
For Latin-1 only, you can use the
key C-x 8 as a "compose character" prefix for entry of
non-ASCII Latin-1 printing characters. C-x 8 is good for
insertion (in the minibuffer as well as other buffers), for searching,
and in any other context where a key sequence is allowed.
C-x 8 works by loading the iso-transl library. Once that
library is loaded, the ALT modifier key, if you have one, serves
the same purpose as C-x 8; use ALT together with an accent
character to modify the following letter. In addition, if you have keys
for the Latin-1 "dead accent characters," they too are defined to
compose with the following character, once iso-transl is loaded.
Use C-x 8 C-h to list the available translations as mnemonic
command names.
-
For Latin-1, Latin-2 and Latin-3, M-x iso-accents-mode enables
a minor mode that works much like the
latin-1-prefix input
method, but does not depend on having the input methods installed. This
mode is buffer-local. It can be customized for various languages with
M-x iso-accents-customize.
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