1PRECONV(1)                  General Commands Manual                 PRECONV(1)
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NAME

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

SYNOPSIS

10       preconv [-dr] [-D default_encoding] [-e encoding] [file ...]
11       preconv -h
12       preconv --help
13
14       preconv -v
15       preconv --version
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       Whitespace is permitted between a command-line option and its argument.
27
28       -d     Emit  debugging  messages to standard error (mainly the used en‐
29              coding).
30
31       -Dencoding
32              Specify default encoding if everything fails (see below).
33
34       -eencoding
35              Specify input encoding explicitly, overriding all other methods.
36              This  corresponds  to  groff's  -Kencoding option.  Without this
37              switch, preconv uses the algorithm described below to select the
38              input encoding.
39
40       --help
41       -h     Print a help message and exit.
42
43       -r     Do not add .lf requests.
44
45       --version
46       -v     Print the version number and exit.
47

USAGE

49       preconv tries to find the input encoding with the following algorithm.
50
51       1.     If  the input encoding has been explicitly specified with option
52              -e, use it.
53
54       2.     Otherwise, check whether the input starts with a Byte Order Mark
55              (BOM, see below).  If found, use it.
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57       3.     Otherwise, check whether there is a known coding tag (see below)
58              in either the first or second input line.  If found, use it.
59
60       4      Finally, if the uchardet library (an encoding  detector  library
61              available  on most major distributions) is available on the sys‐
62              tem, use it to try to detect the encoding of the file.
63
64       5.     If everything fails, use a default encoding as given with option
65              -D,  by  the current locale, or ‘latin1’ if the locale is set to
66              ‘C’, ‘POSIX’, or empty (in that order).
67
68       Note that the groff program supports a GROFF_ENCODING environment vari‐
69       able which is eventually expanded to option -k.
70
71   Byte Order Mark
72       The  Unicode  Standard  defines character U+FEFF as the Byte Order Mark
73       (BOM).  On the other hand, value U+FFFE is guaranteed not be a  Unicode
74       character  at  all.  This allows detection of the byte order within the
75       data stream (either big-endian or little-endian), and the  MIME  encod‐
76       ings  ‘UTF-16’  and  ‘UTF-32’  mandate that the data stream starts with
77       U+FEFF.  Similarly, the data stream encoded as ‘UTF-8’ might start with
78       a  BOM  (to ease the conversion from and to UTF-16 and UTF-32).  In all
79       cases, the byte order mark is not part of the data but part of the  en‐
80       coding protocol; in other words, preconv's output doesn't contain it.
81
82       Note  that  U+FEFF not at the start of the input data actually is emit‐
83       ted; it has then the meaning of a ‘zero width no-break space’ character
84       – something not needed normally in groff.
85
86   Coding Tags
87       Editors  which  support more than a single character encoding need tags
88       within the input files to mark the file's encoding.  While it is possi‐
89       ble  to guess the right input encoding with the help of heuristic algo‐
90       rithms for data which represents a greater amount  of  a  natural  lan‐
91       guage,  it  is  still  just a guess.  Additionally, all algorithms fail
92       easily for input which is either too short or doesn't represent a natu‐
93       ral language.
94
95       For  these  reasons,  preconv  supports the coding tag convention (with
96       some restrictions) as used by GNU Emacs and XEmacs (and probably  other
97       programs too).
98
99       Coding  tags in GNU Emacs and XEmacs are stored in so-called File Vari‐
100       ables.  preconv recognizes the following syntax form which must be  put
101       into a troff comment in the first or second line.
102
103              -*- tag1: value1; tag2: value2; ... -*-
104
105       The only relevant tag for preconv is ‘coding’ which can take the values
106       listed below.  Here an example line which tells Emacs to edit a file in
107       troff mode, and to use latin2 as its encoding.
108
109              .\" -*- mode: troff; coding: latin-2 -*-
110
111       The  following list gives all MIME coding tags (either lowercase or up‐
112       percase) supported by preconv; this list is hard-coded in the source.
113
114              big5, cp1047, euc-jp, euc-kr, gb2312, iso-8859-1, iso-8859-2,
115              iso-8859-5, iso-8859-7, iso-8859-9, iso-8859-13, iso-8859-15,
116              koi8-r, us-ascii, utf-8, utf-16, utf-16be, utf-16le
117
118       In addition, the following hard-coded list of other tags is  recognized
119       which eventually map to values from the list above.
120
121              ascii, chinese-big5, chinese-euc, chinese-iso-8bit, cn-big5,
122              cn-gb, cn-gb-2312, cp878, csascii, csisolatin1,
123              cyrillic-iso-8bit, cyrillic-koi8, euc-china, euc-cn, euc-japan,
124              euc-japan-1990, euc-korea, greek-iso-8bit, iso-10646/utf8,
125              iso-10646/utf-8, iso-latin-1, iso-latin-2, iso-latin-5,
126              iso-latin-7, iso-latin-9, japanese-euc, japanese-iso-8bit, jis8,
127              koi8, korean-euc, korean-iso-8bit, latin-0, latin1, latin-1,
128              latin-2, latin-5, latin-7, latin-9, mule-utf-8, mule-utf-16,
129              mule-utf-16be, mule-utf-16-be, mule-utf-16be-with-signature,
130              mule-utf-16le, mule-utf-16-le, mule-utf-16le-with-signature,
131              utf8, utf-16-be, utf-16-be-with-signature,
132              utf-16be-with-signature, utf-16-le, utf-16-le-with-signature,
133              utf-16le-with-signature
134
135       Those  tags  are  taken  from  GNU Emacs and XEmacs, together with some
136       aliases.  Trailing ‘-dos’, ‘-unix’, and ‘-mac’ suffixes of coding  tags
137       (which  give  the end-of-line convention used in the file) are stripped
138       off before the comparison with the above tags happens.
139
140   Iconv Issues
141       preconv by itself only supports three encodings: latin-1,  cp1047,  and
142       UTF-8;  all  other encodings are passed to the iconv library functions.
143       At compile time it is searched and checked for a valid iconv  implemen‐
144       tation; a call to ‘preconv --version’ shows whether iconv is used.
145

BUGS

147       preconv  doesn't support local variable lists yet.  This is a different
148       syntax form to specify local variables at the end of a file.
149

SEE ALSO

151       groff(1)
152       the GNU Emacs and XEmacs info pages
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154
155
156groff 1.22.4                     21 July 2022                       PRECONV(1)
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