1PRECONV(1)                  General Commands Manual                 PRECONV(1)
2
3
4

NAME

6       preconv - convert encoding of input files to something GNU troff under‐
7       stands
8

SYNOPSIS

10       preconv [-dr] [-e encoding] [files ...]
11       preconv -h | --help
12       preconv -v | --version
13
14       It is possible to have whitespace between the -e  command  line  option
15       and its parameter.
16

DESCRIPTION

18       preconv reads files and converts its encoding(s) to a form GNU troff(1)
19       can process, sending the data  to  standard  output.   Currently,  this
20       means ASCII characters and ‘\[uXXXX]’ entities, where ‘XXXX’ is a hexa‐
21       decimal number with four to six digits, representing  a  Unicode  input
22       code.   Normally,  preconv should be invoked with the -k and -K options
23       of groff.
24

OPTIONS

26       -d     Emit debugging messages  to  standard  error  (mainly  the  used
27              encoding).
28
29       -Dencoding
30              Specify default encoding if everything fails (see below).
31
32       -eencoding
33              Specify input encoding explicitly, overriding all other methods.
34              This corresponds to groff's  -Kencoding  option.   Without  this
35              switch, preconv uses the algorithm described below to select the
36              input encoding.
37
38       --help
39       -h     Print help message.
40
41       -r     Do not add .lf requests.
42
43       --version
44       -v     Print version number.
45

USAGE

47       preconv tries to find the input encoding with the following algorithm.
48
49       1.     If the input encoding has been explicitly specified with  option
50              -e, use it.
51
52       2.     Otherwise, check whether the input starts with a Byte Order Mark
53              (BOM, see below).  If found, use it.
54
55       3.     Finally, check whether there is a known coding tag  (see  below)
56              in either the first or second input line.  If found, use it.
57
58       4.     If everything fails, use a default encoding as given with option
59              -D, by the current locale, or ‘latin1’ if the locale is  set  to
60              ‘C’, ‘POSIX’, or empty (in that order).
61
62       Note that the groff program supports a GROFF_ENCODING environment vari‐
63       able which is eventually expanded to option -k.
64
65   Byte Order Mark
66       The Unicode Standard defines character U+FEFF as the  Byte  Order  Mark
67       (BOM).   On the other hand, value U+FFFE is guaranteed not be a Unicode
68       character at all.  This allows to detect the byte order within the data
69       stream  (either  big-endian  or  lower-endian),  and the MIME encodings
70       ‘UTF-16’ and ‘UTF-32’ mandate that the data stream starts with  U+FEFF.
71       Similarly,  the  data  stream encoded as ‘UTF-8’ might start with a BOM
72       (to ease the conversion from and to UTF-16 and UTF-32).  In all  cases,
73       the  byte  order  mark is not part of the data but part of the encoding
74       protocol; in other words, preconv's output doesn't contain it.
75
76       Note that U+FEFF not at the start of the input data actually  is  emit‐
77       ted; it has then the meaning of a ‘zero width no-break space’ character
78       – something not needed normally in groff.
79
80   Coding Tags
81       Editors which support more than a single character encoding  need  tags
82       within the input files to mark the file's encoding.  While it is possi‐
83       ble to guess the right input encoding with the help of heuristic  algo‐
84       rithms  for  data  which  represents a greater amount of a natural lan‐
85       guage, it is still just a guess.   Additionally,  all  algorithms  fail
86       easily for input which is either too short or doesn't represent a natu‐
87       ral language.
88
89       For these reasons, preconv supports the  coding  tag  convention  (with
90       some  restrictions) as used by GNU Emacs and XEmacs (and probably other
91       programs too).
92
93       Coding tags in GNU Emacs and XEmacs are stored in so-called File  Vari‐
94       ables.   preconv recognizes the following syntax form which must be put
95       into a troff comment in the first or second line.
96
97              -*- tag1: value1; tag2: value2; ... -*-
98
99       The only relevant tag for preconv is ‘coding’ which can take the values
100       listed below.  Here an example line which tells Emacs to edit a file in
101       troff mode, and to use latin2 as its encoding.
102
103              .\" -*- mode: troff; coding: latin-2 -*-
104
105       The following list gives all MIME  coding  tags  (either  lowercase  or
106       uppercase) supported by preconv; this list is hard-coded in the source.
107
108              big5, cp1047, euc-jp, euc-kr, gb2312, iso-8859-1, iso-8859-2,
109              iso-8859-5, iso-8859-7, iso-8859-9, iso-8859-13, iso-8859-15,
110              koi8-r, us-ascii, utf-8, utf-16, utf-16be, utf-16le
111
112       In  addition, the following hard-coded list of other tags is recognized
113       which eventually map to values from the list above.
114
115              ascii, chinese-big5, chinese-euc, chinese-iso-8bit, cn-big5,
116              cn-gb, cn-gb-2312, cp878, csascii, csisolatin1,
117              cyrillic-iso-8bit, cyrillic-koi8, euc-china, euc-cn, euc-japan,
118              euc-japan-1990, euc-korea, greek-iso-8bit, iso-10646/utf8,
119              iso-10646/utf-8, iso-latin-1, iso-latin-2, iso-latin-5,
120              iso-latin-7, iso-latin-9, japanese-euc, japanese-iso-8bit, jis8,
121              koi8, korean-euc, korean-iso-8bit, latin-0, latin1, latin-1,
122              latin-2, latin-5, latin-7, latin-9, mule-utf-8, mule-utf-16,
123              mule-utf-16be, mule-utf-16-be, mule-utf-16be-with-signature,
124              mule-utf-16le, mule-utf-16-le, mule-utf-16le-with-signature,
125              utf8, utf-16-be, utf-16-be-with-signature,
126              utf-16be-with-signature, utf-16-le, utf-16-le-with-signature,
127              utf-16le-with-signature
128
129       Those tags are taken from GNU Emacs  and  XEmacs,  together  with  some
130       aliases.   Trailing ‘-dos’, ‘-unix’, and ‘-mac’ suffixes of coding tags
131       (which give the end-of-line convention used in the file)  are  stripped
132       off before the comparison with the above tags happens.
133
134   Iconv Issues
135       preconv  by  itself only supports three encodings: latin-1, cp1047, and
136       UTF-8; all other encodings are passed to the iconv  library  functions.
137       At  compile time it is searched and checked for a valid iconv implemen‐
138       tation; a call to ‘preconv --version’ shows whether iconv is used.
139

BUGS

141       preconv doesn't support local variable lists yet.  This is a  different
142       syntax form to specify local variables at the end of a file.
143

SEE ALSO

145       groff(1)
146       the GNU Emacs and XEmacs info pages
147

COPYING

149       Copyright © 2006-2014 Free Software Foundation, Inc.
150
151       Permission  is  granted  to make and distribute verbatim copies of this
152       manual provided the copyright notice and  this  permission  notice  are
153       preserved on all copies.
154
155       Permission  is granted to copy and distribute modified versions of this
156       manual under the conditions for verbatim  copying,  provided  that  the
157       entire  resulting derived work is distributed under the terms of a per‐
158       mission notice identical to this one.
159
160       Permission is granted to copy and distribute translations of this  man‐
161       ual into another language, under the above conditions for modified ver‐
162       sions, except that this permission notice may be included  in  transla‐
163       tions approved by the Free Software Foundation instead of in the origi‐
164       nal English.
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168Groff Version 1.22.3            4 November 2014                     PRECONV(1)
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