PRECONV(1) | General Commands Manual | PRECONV(1) |
preconv - convert encoding of input files to something GNU troff understands
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 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.
Whitespace is permitted between a command-line option and its argument.
preconv tries to find the input encoding with the following algorithm.
Note that the groff program supports a GROFF_ENCODING environment variable which is eventually expanded to option -k.
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.
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, 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.
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 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.
groff(1)
the GNU Emacs and XEmacs info pages
7 March 2023 | groff 1.22.4 |