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
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.
--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
1. If the input encoding has been explicitly specified with
option -e, use it.
2. Otherwise, check whether the input starts with a Byte OrderMark (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.
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 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 FileVariables. 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
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 recog‐
nized 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,
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.
Iconv Issuespreconv 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 imple‐
mentation; a call to ‘preconv --version’ shows whether iconv is used.
This page is part of the groff (GNU troff) project. Information
about the project can be found at
⟨http://www.gnu.org/software/groff/⟩. If you have a bug report for
this manual page, see ⟨http://www.gnu.org/software/groff/⟩. This
page was obtained from the tarball groff-1.22.3.tar.gz fetched from
⟨ftp://ftp.gnu.org/gnu/groff/⟩ on 2016-09-01. If you discover any
rendering problems in this HTML version of the page, or you believe
there is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
Groff Version 1.22.3 4 November 2014 PRECONV(1)