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PRECONV(1)									       PRECONV(1)

NAME
       preconv - convert encoding of input files to something GNU troff understands

SYNOPSIS
       preconv [-dr] [-e encoding] [files ...]
       preconv -h | --help
       preconv -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, send-
       ing 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.

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'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 `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  even-
       tually 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.   Simi-
       larly,  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.

   Coding Tags
       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 nat-
       ural 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  rec-
       ognizes	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, 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.

   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 `preconv --version' shows whether
       iconv is used.

BUGS
       preconv doesn'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

Groff Version 1.22.2			 7 February 2013			       PRECONV(1)
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