PRECONV(1)		    General Commands Manual		    PRECONV(1)



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

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, sending the data  to  standard  output.   Currently,  this
       means ASCII characters and `\[uXXXX]' entities, where `XXXX' is a hexa-
       decimal 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 vari-
       able 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	 emit-
       ted; 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 possi-
       ble to guess the right input encoding with the help of heuristic	 algo-
       rithms  for  data  which	 represents a greater amount of a natural lan-
       guage, it is still just a guess.	  Additionally,	 all  algorithms  fail
       easily for input which is either too short or doesn't represent a natu-
       ral 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	 Vari-
       ables.	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,
	      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 implemen-
       tation; 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)