PRECONV
Section: User Commands (1)
Updated: 4 November 2014
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NAME
preconv - convert encoding of input files to something GNU troff understands
SYNOPSIS
[
-dr ]
[
-e encoding ]
[
files
...]
-h
|
--help
-v
|
--version
It is possible to have whitespace between the
-e
command line option and its parameter.
DESCRIPTION
preconv
reads
files
and converts its encoding(s) to a form GNU
troff(1)
can process, sending the data to standard output.
Currently, this means ASCII characters and [oq]\[uXXXX][cq]
entities, where [oq]XXXX[cq] is a hexadecimal number with four to
six digits, representing a Unicode input code.
Normally,
preconv
should be invoked with the
-k
and
-K
options of
groff.
OPTIONS
- -d
-
Emit debugging messages to standard error (mainly the used encoding).
- -Dencoding
-
Specify default encoding if everything fails (see below).
- -eencoding
-
Specify input encoding explicitly, overriding all other methods.
This corresponds to
groff[aq]s
-Kencoding
option.
Without this switch,
preconv
uses the algorithm described below to select the input encoding.
- --help
-
-h
Print help message.
- -r
-
Do not add .lf requests.
- --version
-
-v
Print version number.
USAGE
preconv
tries to find the input encoding with the following algorithm.
- 1.
-
If the input encoding has been explicitly specified with option
-e,
use it.
- 2.
-
Otherwise, check whether the input starts with a
Byte Order Mark
(BOM, see below).
If found, use it.
- 3.
-
Finally, check whether there is a known
coding tag
(see below) in either the first or second input line.
If found, use it.
- 4.
-
If everything fails, use a default encoding as given with option
-D,
by the current locale, or [oq]latin1[cq] if the locale is set to
[oq]C[cq], [oq]POSIX[cq], or empty (in that order).
Note that the
groff
program supports a
GROFF_ENCODING
environment variable which is eventually expanded to option
-k.
Byte Order Mark
The Unicode Standard defines character U+FEFF as the Byte Order Mark
(BOM).
On the other hand, value U+FFFE is guaranteed not be a Unicode character at
all.
This allows to detect the byte order within the data stream (either
big-endian or lower-endian), and the MIME encodings [oq]UTF-16[cq]
and [oq]UTF-32[cq] mandate that the data stream starts with U+FEFF.
Similarly, the data stream encoded as [oq]UTF-8[cq] might start
with a BOM (to ease the conversion from and to UTF-16 and UTF-32).
In all cases, the byte order mark is
not
part of the data but part of the encoding protocol; in other words,
preconv[aq]s
output doesn[aq]t contain it.
Note that U+FEFF not at the start of the input data actually is
emitted; it has then the meaning of a [oq]zero width no-break
space[cq] character [en] something not needed normally in
groff.
Coding Tags
Editors which support more than a single character encoding need tags
within the input files to mark the file[aq]s encoding.
While it is possible to guess the right input encoding with the help of
heuristic algorithms for data which represents a greater amount of a natural
language, it is still just a guess.
Additionally, all algorithms fail easily for input which is either too short
or doesn[aq]t represent a natural language.
For these reasons,
preconv
supports the coding tag convention (with some restrictions) as used by
GNU Emacs
and
XEmacs
(and probably other programs too).
Coding tags in
GNU Emacs
and
XEmacs
are stored in so-called
File Variables.
preconv
recognizes the following syntax form which must be put into a troff comment
in the first or second line.
-
-*-
tag1:
value1;
tag2:
value2;
... -*-
The only relevant tag for
preconv
is [oq]coding[cq] which can take the values listed below.
Here an example line which tells
Emacs
to edit a file in troff mode, and to use latin2 as its encoding.
-
.[rs]" -*- mode: troff; coding: latin-2 -*-
The following list gives all MIME coding tags (either lowercase or
uppercase) supported by
preconv;
this list is hard-coded in the source.
-
big5, cp1047, euc-jp, euc-kr, gb2312, iso-8859-1,
iso-8859-2, iso-8859-5, iso-8859-7, iso-8859-9, iso-8859-13,
iso-8859-15, koi8-r, us-ascii, utf-8, utf-16, utf-16be,
utf-16le
In addition, the following hard-coded list of other tags is recognized
which eventually map to values from the list above.
-
ascii, chinese-big5, chinese-euc, chinese-iso-8bit, cn-big5,
cn-gb, cn-gb-2312, cp878, csascii, csisolatin1,
cyrillic-iso-8bit, cyrillic-koi8, euc-china, euc-cn,
euc-japan, euc-japan-1990, euc-korea, greek-iso-8bit,
iso-10646/utf8, iso-10646/utf-8, iso-latin-1, iso-latin-2,
iso-latin-5, iso-latin-7, iso-latin-9, japanese-euc,
japanese-iso-8bit, jis8, koi8, korean-euc, korean-iso-8bit,
latin-0, latin1, latin-1, latin-2, latin-5, latin-7,
latin-9, mule-utf-8, mule-utf-16, mule-utf-16be,
mule-utf-16-be, mule-utf-16be-with-signature, mule-utf-16le,
mule-utf-16-le, mule-utf-16le-with-signature, utf8, utf-16-be,
utf-16-be-with-signature, utf-16be-with-signature, utf-16-le,
utf-16-le-with-signature, utf-16le-with-signature
Those tags are taken from
GNU Emacs
and
XEmacs,
together with some aliases.
Trailing [oq]-dos[cq], [oq]-unix[cq], and [oq]-mac[cq]
suffixes of coding tags (which give the end-of-line convention used in
the file) are stripped off before the comparison with the above tags
happens.
Iconv Issues
preconv
by itself only supports three encodings: latin-1, cp1047, and UTF-8;
all other encodings are passed to the
iconv
library functions.
At compile time it is searched and checked for a valid
iconv
implementation; a call to [oq]preconv --version[cq] shows whether
iconv
is used.
BUGS
preconv
doesn[aq]t support
local variable lists
yet.
This is a different syntax form to specify local variables at the end of a
file.
SEE ALSO
groff(1)
the
GNU Emacs
and
XEmacs
info pages
COPYING
Copyright [co] 2006-2014 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of
this manual provided the copyright notice and this permission notice
are preserved on all copies.
Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.
Permission is granted to copy and distribute translations of this
manual into another language, under the above conditions for modified
versions, except that this permission notice may be included in
translations approved by the Free Software Foundation instead of in
the original English.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- OPTIONS
-
- USAGE
-
- Byte Order Mark
-
- Coding Tags
-
- Iconv Issues
-
- BUGS
-
- SEE ALSO
-
- COPYING
-
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