PRECONV(1)                 General Commands Manual                PRECONV(1)

NAME         top

       preconv  -  convert  encoding  of  input files to something GNU troff

SYNOPSIS         top

       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         top

       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.

OPTIONS         top

       -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.

USAGE         top

       preconv tries to find the input encoding with the following

       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 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 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

              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 recog‐
       nized 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 imple‐
       mentation; a call to ‘preconv --version’ shows whether iconv is used.

BUGS         top

       preconv doesn't support local variable lists yet.  This is a
       different syntax form to specify local variables at the end of a

SEE ALSO         top

       the GNU Emacs and XEmacs info pages

COLOPHON         top

       This page is part of the groff (GNU troff) project.  Information
       about the project can be found at 
       ⟨⟩.  If you have a bug report for
       this manual page, see ⟨⟩.  This
       page was obtained from the project's upstream Git repository
       ⟨⟩ on 2018-10-29.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2018-10-25.)  If you discover any rendering problems in
       this HTML version of the page, or you believe there is a better or
       more up-to-date source for the page, or you have corrections or
       improvements to the information in this COLOPHON (which is not part
       of the original manual page), send a mail to

Groff Version 1.22.3          24 November 2017                    PRECONV(1)

Pages that refer to this page: groff(1)