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VIS(3)			 BSD Library Functions Manual			VIS(3)

NAME
     vis — visually encode characters

SYNOPSIS
     #include <vis.h>

     char *
     vis(char *dst, char c, int flag, char nextc);

     int
     strvis(char *dst, char *src, int flag);

     int
     strvisx(char *dst, char *src, int len, int flag);

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 characters (not including the
     trailing NULL); thus, when encoding a set of characters into a buffer,
     the size of the buffer should be four times the number of characters
     encoded, plus one for the trailing NULL.  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() and strvisx() functions copy into dst a visual representa‐
     tion of the string src.  The strvis() function encodes characters from
     src up to the first NULL.	The strvisx() function encodes exactly len
     characters from src (this is useful for encoding a block of data that may
     contain NULL's). Both forms NULL terminate dst.  The size of dst must be
     four times the number of characters encoded from src (plus one for the
     NULL).  Both forms return the number of characters in dst (not including
     the trailing NULL).

     The encoding is a unique, invertible representation comprised 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_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.  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.

     There are three forms of encoding.	 All forms use the backslash character
     ‘\’ to introduce a special sequence; two backslashes are used to repre‐
     sent a real backslash.  These are the visual formats:

     (default)	 Use an ‘M’ to represent meta characters (characters with the
		 8th bit set), and use carat ‘^’ 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)
		       \t - HT (011)
		       \v - VT (013)
		       \0 - NUL (000)

		 When using this format, the nextc parameter is looked at to
		 determine if a NULL character can be encoded as ‘\0’ instead
		 of ‘\000’.  If nextc is an octal digit, the latter represen‐
		 tation 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), unvis(3) strunvis(3)

HISTORY
     These functions first appeared in 4.4BSD.

BSD				 June 9, 1993				   BSD
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