vis(3bsd) LOCAL vis(3bsd)
NAME
vis, nvis, strvis, stravis, strnvis, strvisx, strnvisx, strenvisx, svis,
snvis, strsvis, strsnvis, strsvisx, strsnvisx, strsenvisx — visually en-
code characters
LIBRARY
Utility functions from BSD systems (libbsd, -lbsd)
SYNOPSIS
#include <vis.h>
(See libbsd(7) for include usage.)
char *
vis(char *dst, int c, int flag, int nextc);
char *
nvis(char *dst, size_t dlen, int c, int flag, int nextc);
int
strvis(char *dst, const char *src, int flag);
int
stravis(char **dst, const char *src, int flag);
int
strnvis(char *dst, size_t dlen, const char *src, int flag);
int
strvisx(char *dst, const char *src, size_t len, int flag);
int
strnvisx(char *dst, size_t dlen, const char *src, size_t len, int flag);
int
strenvisx(char *dst, size_t dlen, const char *src, size_t len, int flag,
int *cerr_ptr);
char *
svis(char *dst, int c, int flag, int nextc, const char *extra);
char *
snvis(char *dst, size_t dlen, int c, int flag, int nextc,
const char *extra);
int
strsvis(char *dst, const char *src, int flag, const char *extra);
int
strsnvis(char *dst, size_t dlen, const char *src, int flag,
const char *extra);
int
strsvisx(char *dst, const char *src, size_t len, int flag,
const char *extra);
int
strsnvisx(char *dst, size_t dlen, const char *src, size_t len, int flag,
const char *extra);
int
strsenvisx(char *dst, size_t dlen, const char *src, size_t len, int flag,
const char *extra, int *cerr_ptr);
DESCRIPTION
The vis() function copies into dst a string which represents the charac-
ter c. If c needs no encoding, it is copied in unaltered. The string is
null terminated, and a pointer to the end of the string is returned. The
maximum length of any encoding is four bytes (not including the trailing
NUL); thus, when encoding a set of characters into a buffer, the size of
the buffer should be four times the number of bytes encoded, plus one for
the trailing NUL. The flag parameter is used for altering the default
range of characters considered for encoding and for altering the visual
representation. The additional character, nextc, is only used when se-
lecting the VIS_CSTYLE encoding format (explained below).
The strvis(), stravis(), strnvis(), strvisx(), and strnvisx() functions
copy into dst a visual representation of the string src. The strvis()
and strnvis() functions encode characters from src up to the first NUL.
The strvisx() and strnvisx() functions encode exactly len characters from
src (this is useful for encoding a block of data that may contain NUL's).
Both forms NUL terminate dst. The size of dst must be four times the
number of bytes encoded from src (plus one for the NUL). Both forms re-
turn the number of characters in dst (not including the trailing NUL).
The stravis() function allocates space dynamically to hold the string.
The “n” versions of the functions also take an additional argument dlen
that indicates the length of the dst buffer. If dlen is not large enough
to fit the converted string then the strnvis() and strnvisx() functions
return -1 and set errno to ENOSPC. The strenvisx() function takes an ad-
ditional argument, cerr_ptr, that is used to pass in and out a multibyte
conversion error flag. This is useful when processing single characters
at a time when it is possible that the locale may be set to something
other than the locale of the characters in the input data.
The functions svis(), snvis(), strsvis(), strsnvis(), strsvisx(),
strsnvisx(), and strsenvisx() correspond to vis(), nvis(), strvis(),
strnvis(), strvisx(), strnvisx(), and strenvisx() but have an additional
argument extra, pointing to a NUL terminated list of characters. These
characters will be copied encoded or backslash-escaped into dst. These
functions are useful e.g. to remove the special meaning of certain char-
acters to shells.
The encoding is a unique, invertible representation composed entirely of
graphic characters; it can be decoded back into the original form using
the unvis(3bsd), strunvis(3bsd) or strnunvis(3bsd) functions.
There are two parameters that can be controlled: the range of characters
that are encoded (applies only to vis(), nvis(), strvis(), strnvis(),
strvisx(), and strnvisx()), and the type of representation used. By de-
fault, all non-graphic characters, except space, tab, and newline are en-
coded (see isgraph(3)). The following flags alter this:
VIS_DQ Also encode double quotes
VIS_GLOB Also encode the magic characters (‘*’, ‘?’, ‘[’, and ‘#’)
recognized by glob(3).
VIS_SHELL Also encode the meta characters used by shells (in addition
to the glob characters): (‘'’, ‘`’, ‘"’, ‘;’, ‘&’, ‘<’, ‘>’,
‘(’, ‘)’, ‘|’, ‘]’, ‘\’, ‘$’, ‘!’, ‘^’, and ‘~’).
VIS_SP Also encode space.
VIS_TAB Also encode tab.
VIS_NL Also encode newline.
VIS_WHITE Synonym for VIS_SP | VIS_TAB | VIS_NL.
VIS_META Synonym for VIS_WHITE | VIS_GLOB | VIS_SHELL.
VIS_SAFE Only encode “unsafe” characters. Unsafe means control char-
acters which may cause common terminals to perform unexpected
functions. Currently this form allows space, tab, newline,
backspace, bell, and return — in addition to all graphic
characters — unencoded.
(The above flags have no effect for svis(), snvis(), strsvis(),
strsnvis(), strsvisx(), and strsnvisx(). When using these functions,
place all graphic characters to be encoded in an array pointed to by
extra. In general, the backslash character should be included in this
array, see the warning on the use of the VIS_NOSLASH flag below).
There are six forms of encoding. All forms use the backslash character
‘\’ to introduce a special sequence; two backslashes are used to repre-
sent a real backslash, except VIS_HTTPSTYLE that uses ‘%’, or
VIS_MIMESTYLE that uses ‘=’. These are the visual formats:
(default) Use an ‘M’ to represent meta characters (characters with the
8th bit set), and use caret ‘^’ to represent control charac-
ters (see iscntrl(3)). The following formats are used:
\^C Represents the control character ‘C’. Spans charac-
ters ‘\000’ through ‘\037’, and ‘\177’ (as ‘\^?’).
\M-C Represents character ‘C’ with the 8th bit set. Spans
characters ‘\241’ through ‘\376’.
\M^C Represents control character ‘C’ with the 8th bit set.
Spans characters ‘\200’ through ‘\237’, and ‘\377’ (as
‘\M^?’).
\040 Represents ASCII space.
\240 Represents Meta-space.
VIS_CSTYLE Use C-style backslash sequences to represent standard non-
printable characters. The following sequences are used to
represent the indicated characters:
\a — BEL (007)
\b — BS (010)
\f — NP (014)
\n — NL (012)
\r — CR (015)
\s — SP (040)
\t — HT (011)
\v — VT (013)
\0 — NUL (000)
When using this format, the nextc parameter is looked at to
determine if a NUL character can be encoded as ‘\0’ instead
of ‘\000’. If nextc is an octal digit, the latter represen-
tation is used to avoid ambiguity.
Non-printable characters without C-style backslash sequences
use the default representation.
VIS_OCTAL Use a three digit octal sequence. The form is ‘\ddd’ where d
represents an octal digit.
VIS_CSTYLE | VIS_OCTAL
Same as VIS_CSTYLE except that non-printable characters with-
out C-style backslash sequences use a three digit octal se-
quence.
VIS_HTTPSTYLE
Use URI encoding as described in RFC 1738. The form is ‘%xx’
where x represents a lower case hexadecimal digit.
VIS_MIMESTYLE
Use MIME Quoted-Printable encoding as described in RFC 2045,
only don't break lines and don't handle CRLF. The form is
‘=XX’ where X represents an upper case hexadecimal digit.
There is one additional flag, VIS_NOSLASH, which inhibits the doubling of
backslashes and the backslash before the default format (that is, control
characters are represented by ‘^C’ and meta characters as ‘M-C’). With
this flag set, the encoding is ambiguous and non-invertible.
MULTIBYTE CHARACTER SUPPORT
These functions support multibyte character input. The encoding conver-
sion is influenced by the setting of the LC_CTYPE environment variable
which defines the set of characters that can be copied without encoding.
If VIS_NOLOCALE is set, processing is done assuming the C locale and
overriding any other environment settings.
When 8-bit data is present in the input, LC_CTYPE must be set to the cor-
rect locale or to the C locale. If the locales of the data and the con-
version are mismatched, multibyte character recognition may fail and en-
coding will be performed byte-by-byte instead.
As noted above, dst must be four times the number of bytes processed from
src. But note that each multibyte character can be up to MB_LEN_MAX
bytes so in terms of multibyte characters, dst must be four times
MB_LEN_MAX times the number of characters processed from src.
ENVIRONMENT
LC_CTYPE Specify the locale of the input data. Set to C if the input
data locale is unknown.
ERRORS
The functions nvis() and snvis() will return NULL and the functions
strnvis(), strnvisx(), strsnvis(), and strsnvisx(), will return -1 when
the dlen destination buffer size is not enough to perform the conversion
while setting errno to:
[ENOSPC] The destination buffer size is not large enough to perform the
conversion.
SEE ALSO
unvis(1), vis(1), glob(3), unvis(3bsd)
T. Berners-Lee, Uniform Resource Locators (URL), RFC 1738.
Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet
Message Bodies, RFC 2045.
HISTORY
The vis(), strvis(), and strvisx() functions first appeared in 4.4BSD.
The svis(), strsvis(), and strsvisx() functions appeared in NetBSD 1.5.
The buffer size limited versions of the functions (nvis(), strnvis(),
strnvisx(), snvis(), strsnvis(), and strsnvisx()) appeared in NetBSD 6.0
and FreeBSD 9.2. Multibyte character support was added in NetBSD 7.0 and
FreeBSD 9.2.
BSD April 22, 2017 BSD
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