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PRECONV(1)		    General Commands Manual		    PRECONV(1)

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

       preconv [-dr] [-D default_encoding] [-e encoding] [file ...]
       preconv -h
       preconv --help

       preconv -v
       preconv --version

       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.

       Whitespace is permitted between a command-line option and its argument.

       -d     Emit  debugging  messages	to standard error (mainly the used en-

	      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.

       -h     Print a help message and exit.

       -r     Do not add .lf requests.

       -v     Print the	version	number and exit.

       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.     Otherwise, check whether there is	a known	coding tag (see	below)
	      in either	the first or second input line.	 If found, use it.

       4      Finally, if the uchardet library (an encoding  detector  library
	      available	 on most major distributions) is available on the sys-
	      tem, use it to try to detect the encoding	of the file.

       5.     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	detection of the byte order within the
       data stream (either big-endian or little-endian), and the  MIME	encod-
       ings  `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  en-
       coding 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 up-
       percase)	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.

   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.

       preconv	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

groff 1.22.4		       18 November 2018			    PRECONV(1)


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