Provided by: groff-base_1.22.4-8build1_amd64 bug


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


       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  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.


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

       -d     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.

       -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 system,  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  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 detection
       of  the  byte  order  within the data stream (either big-endian or little-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

   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
       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, 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.


       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