PRECONV(1) manual page
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preconv - convert encoding of input files to something GNU troff
understands
[files ...] -h | --help -v | --version
It is possible
to have whitespace between the -e command line option and its parameter.
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 ‘\[uXXXX]’ entities, where ‘XXXX’ 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.
- -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’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.
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 ‘latin1’ if the locale is set to ‘C’, ‘POSIX’, or empty (in that order).
Note
that the groff program supports a GROFF_ENCODING environment variable which
is eventually expanded to option -k.
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 ‘UTF-16’ and ‘UTF-32’ mandate that the data stream starts
with U+FEFF. Similarly, the data stream encoded as ‘UTF-8’ 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’s output doesn’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 ‘zero width no-break space’ character [en] something not needed normally
in groff.
Editors which support more than a single character
encoding need tags within the input files to mark the file’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’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 ‘coding’ 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 ‘-dos’, ‘-unix’,
and ‘-mac’ 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.
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 ‘preconv --version’ shows whether iconv is used.
preconv doesn’t
support local variable lists yet. This is a different syntax form to specify
local variables at the end of a file.
groff(1)
the GNU Emacs and XEmacs info pages
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