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                     21 March 2020                      PRECONV(1)
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