convert encoding of input files to something GNU troff understands
see also :
[-e encoding] [files
-h | --help
-v | --version
It is possible
to have whitespace between the -e command line
option and its parameter.
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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
Emit debugging messages to
standard error (mainly the used encoding).
Specify default encoding if
everything fails (see below).
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.
Print help message.
Do not add .lf requests.
preconv tries to find the input encoding with the
If the input encoding has been explicitly specified with option
-e, use it.
Otherwise, check whether the input starts with a Byte Order
Mark (BOM, see below). If found, use it.
Finally, check whether there is a known coding tag (see
below) in either the first or second input line. If found, use
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.
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 ’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 – something not needed normally in
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.
.\" -*- 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,
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
doesn’t support local variable lists yet. This
is a different syntax form to specify local variables at the
end of a file.
the GNU Emacs and XEmacs info pages