VIS(1) BSD General Commands Manual VIS(1)
NAME
vis -- display non-printable characters in a visual format
SYNOPSIS
vis [-bcfhlmnostw] [-e extra] [-F foldwidth] [file ...]
DESCRIPTION
vis is a filter for converting non-printable characters into a visual representation. It differs from 'cat -v' in that the form is unique
and invertible. By default, all non-graphic characters except space, tab, and newline are encoded. A detailed description of the various
visual formats is given in vis(3).
The options are as follows:
-b Turns off prepending of backslash before up-arrow control sequences and meta characters, and disables the doubling of backslashes.
This produces output which is neither invertible or precise, but does represent a minimum of change to the input. It is similar to
``cat -v''. (VIS_NOSLASH)
-c Request a format which displays a small subset of the non-printable characters using C-style backslash sequences. (VIS_CSTYLE)
-e extra
Also encode characters in extra, per svis(3).
-F foldwidth
Causes vis to fold output lines to foldwidth columns (default 80), like fold(1), except that a hidden newline sequence is used,
(which is removed when inverting the file back to its original form with unvis(1)). If the last character in the encoded file does
not end in a newline, a hidden newline sequence is appended to the output. This makes the output usable with various editors and
other utilities which typically don't work with partial lines.
-f Same as -F.
-h Encode using the URI encoding from RFC 1808. (VIS_HTTPSTYLE)
-l Mark newlines with the visible sequence '$', followed by the newline.
-m Encode using the MIME Quoted-Printable encoding from RFC 2045. (VIS_MIMESTYLE)
-n Turns off any encoding, except for the fact that backslashes are still doubled and hidden newline sequences inserted if -f or -F is
selected. When combined with the -f flag, vis becomes like an invertible version of the fold(1) utility. That is, the output can be
unfolded by running the output through unvis(1).
-o Request a format which displays non-printable characters as an octal number, ddd. (VIS_OCTAL)
-s Only characters considered unsafe to send to a terminal are encoded. This flag allows backspace, bell, and carriage return in addi-
tion to the default space, tab and newline. (VIS_SAFE)
-t Tabs are also encoded. (VIS_TAB)
-w White space (space-tab-newline) is also encoded. (VIS_WHITE)
SEE ALSO
unvis(1), svis(3), vis(3)
HISTORY
The vis command appears in 4.4BSD.
BSD
February 10, 2009 BSD
Check Out this Related Man Page
VIS(3) BSD Library Functions Manual VIS(3)
NAME
vis, strvis, strnvis, strvisx -- visually encode characters
LIBRARY
Utility functions from BSD systems (libbsd, -lbsd)
SYNOPSIS
#include <stdlib.h>
#include <bsd/vis.h>
char *
vis(char *dst, int c, int flag, int nextc);
int
strvis(char *dst, const char *src, int flag);
int
strnvis(char *dst, const char *src, size_t size, int flag);
int
strvisx(char *dst, const char *src, size_t len, int flag);
DESCRIPTION
The vis() function copies into dst a string which represents the character c. If c needs no encoding, it is copied in unaltered. The string
is NUL terminated and a pointer to the end of the string is returned. The maximum length of any encoding is four characters (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 charac-
ters 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 selecting the VIS_CSTYLE encoding format
(explained below).
The strvis(), strnvis() and strvisx() functions copy into dst a visual representation of the string src. The strvis() function encodes char-
acters from src up to the first NUL. The strnvis() function encodes characters from src up to the first NUL or the end of dst, as indicated
by size. The strvisx() function encodes exactly len characters from src (this is useful for encoding a block of data that may contain NULs).
All three forms NUL terminate dst, except for strnvis() when size is zero, in which case dst is not touched. For strvis() and strvisx(), the
size of dst must be four times the number of characters encoded from src (plus one for the NUL). strvis() and strvisx() return the number of
characters in dst (not including the trailing NUL). strnvis() returns the length that dst would become if it were of unlimited size (similar
to snprintf(3) or strlcpy(3)). This can be used to detect truncation but it also means that the return value of strnvis() must not be used
without checking it against size.
The encoding is a unique, invertible representation composed entirely of graphic characters; it can be decoded back into the original form
using the unvis(3) or strunvis(3) functions.
There are two parameters that can be controlled: the range of characters that are encoded, and the type of representation used. By default,
all non-graphic characters except space, tab, and newline are encoded (see isgraph(3)). The following flags alter this:
VIS_GLOB Also encode magic characters recognized by glob(3) ('*', '?', '[') 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_SAFE Only encode ``unsafe'' characters. These are control characters which may cause common terminals to perform unexpected func-
tions. Currently this form allows space, tab, newline, backspace, bell, and return -- in addition to all graphic characters --
unencoded.
There are three forms of encoding. All forms use the backslash '' character to introduce a special sequence; two backslashes are used to
represent a real backslash. These are the visual formats:
(default) Use an 'M' to represent meta characters (characters with the 8th bit set), and use a caret '^' to represent control characters
(see iscntrl(3)). The following formats are used:
^C Represents the control character 'C'. Spans characters ' 00' through ' 37', 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^?').
40 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)
- BS (010)
f - NP (014)
- NL (012)
- CR (015)
s - SP (040)
- HT (011)
v - VT (013)
- NUL (000)
When using this format, the nextc parameter is looked at to determine if a NUL character can be encoded as ' ' instead of
' 00'. If nextc is an octal digit, the latter representation is used to avoid ambiguity.
VIS_OCTAL Use a three digit octal sequence. The form is 'ddd' where d represents an octal 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.
SEE ALSO
unvis(1), vis(1), snprintf(3), strlcpy(3), unvis(3)
HISTORY
The vis(), strvis() and strvisx() functions first appeared in 4.4BSD. The strnvis() function first appeared in OpenBSD 2.9.
BSD
May 31, 2007 BSD