Provided by: groff-base_1.22.3-7_i386 bug


       preconv  -  convert  encoding  of  input  files  to something GNU troff


       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.


       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.

       -h     Print help message.

       -r     Do not add .lf requests.

       -v     Print version number.


       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 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.

   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,

       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


       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


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