278 lines
6.7 KiB
Groff
278 lines
6.7 KiB
Groff
.\" Copyright (c) 1989, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" From: @(#)vis.3 8.1 (Berkeley) 6/9/93
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.\" $FreeBSD$
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.\"
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.Dd July 25, 1996
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.Dt VIS 3
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.Os
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.Sh NAME
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.Nm vis
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.Nd visually encode characters
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.Fd #include <vis.h>
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.Ft char *
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.Fn vis "char *dst" "int c" "int flag" "int nextc"
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.Ft int
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.Fn strvis "char *dst" "const char *src" "int flag"
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.Ft int
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.Fn strvisx "char *dst" "const char *src" "size_t len" "int flag"
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.Sh DESCRIPTION
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The
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.Fn vis
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function
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copies into
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.Fa dst
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a string which represents the character
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.Fa c .
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If
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.Fa c
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needs no encoding, it is copied in unaltered. The string is
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null terminated, and a pointer to the end of the string is
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returned. The maximum length of any encoding is four
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characters (not including the trailing
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.Dv NUL ) ;
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thus, when
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encoding a set of characters into a buffer, the size of the buffer should
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be four times the number of characters encoded, plus one for the trailing
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.Dv NUL .
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The flag parameter is used for altering the default range of
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characters considered for encoding and for altering the visual
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representation.
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The additional character,
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.Fa nextc ,
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is only used when selecting the
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.Dv VIS_CSTYLE
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encoding format (explained below).
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.Pp
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The
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.Fn strvis
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and
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.Fn strvisx
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functions copy into
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.Fa dst
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a visual representation of
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the string
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.Fa src .
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The
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.Fn strvis
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function encodes characters from
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.Fa src
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up to the
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first
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.Dv NUL .
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The
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.Fn strvisx
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function encodes exactly
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.Fa len
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characters from
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.Fa src
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(this
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is useful for encoding a block of data that may contain
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.Dv NUL Ns 's ) .
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Both forms
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.Dv NUL
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terminate
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.Fa dst .
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The size of
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.Fa dst
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must be four times the number
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of characters encoded from
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.Fa src
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(plus one for the
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.Dv NUL ) .
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Both
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forms return the number of characters in dst (not including
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the trailing
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.Dv NUL ) .
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.Pp
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The encoding is a unique, invertible representation composed entirely of
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graphic characters; it can be decoded back into the original form using
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the
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.Xr unvis 3
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or
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.Xr strunvis 3
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functions.
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.Pp
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There are two parameters that can be controlled: the range of
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characters that are encoded, and the type
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of representation used.
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By default, all non-graphic characters
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except space, tab, and newline are encoded.
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(See
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.Xr isgraph 3 . )
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The following flags
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alter this:
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.Bl -tag -width VIS_WHITEX
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.It Dv VIS_SP
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Also encode space.
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.It Dv VIS_TAB
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Also encode tab.
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.It Dv VIS_NL
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Also encode newline.
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.It Dv VIS_WHITE
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Synonym for
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.Dv VIS_SP
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\&|
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.Dv VIS_TAB
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\&|
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.Dv VIS_NL .
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.It Dv VIS_SAFE
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Only encode "unsafe" characters. Unsafe means control
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characters which may cause common terminals to perform
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unexpected functions. Currently this form allows space,
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tab, newline, backspace, bell, and return - in addition
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to all graphic characters - unencoded.
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.El
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.Pp
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There are four forms of encoding.
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Most forms use the backslash character
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.Ql \e
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to introduce a special
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sequence; two backslashes are used to represent a real backslash.
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These are the visual formats:
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.Bl -tag -width VIS_HTTPSTYLE
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.It (default)
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Use an
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.Ql M
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to represent meta characters (characters with the 8th
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bit set), and use carat
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.Ql ^
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to represent control characters see
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.Pf ( Xr iscntrl 3 ) .
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The following formats are used:
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.Bl -tag -width xxxxx
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.It Dv \e^C
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Represents the control character
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.Ql C .
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Spans characters
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.Ql \e000
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through
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.Ql \e037 ,
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and
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.Ql \e177
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(as
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.Ql \e^? ) .
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.It Dv \eM-C
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Represents character
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.Ql C
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with the 8th bit set.
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Spans characters
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.Ql \e241
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through
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.Ql \e376 .
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.It Dv \eM^C
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Represents control character
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.Ql C
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with the 8th bit set.
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Spans characters
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.Ql \e200
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through
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.Ql \e237 ,
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and
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.Ql \e377
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(as
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.Ql \eM^? ) .
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.It Dv \e040
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Represents
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.Tn ASCII
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space.
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.It Dv \e240
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Represents Meta-space.
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.El
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.Pp
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.It Dv VIS_CSTYLE
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Use C-style backslash sequences to represent standard non-printable
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characters.
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The following sequences are used to represent the indicated characters:
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.Bd -unfilled -offset indent
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.Li \ea Tn - BEL No (007)
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.Li \eb Tn - BS No (010)
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.Li \ef Tn - NP No (014)
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.Li \en Tn - NL No (012)
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.Li \er Tn - CR No (015)
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.Li \et Tn - HT No (011)
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.Li \ev Tn - VT No (013)
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.Li \e0 Tn - NUL No (000)
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.Ed
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.Pp
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When using this format, the nextc parameter is looked at to determine
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if a
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.Dv NUL
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character can be encoded as
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.Ql \e0
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instead of
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.Ql \e000 .
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If
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.Fa nextc
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is an octal digit, the latter representation is used to
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avoid ambiguity.
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.It Dv VIS_HTTPSTYLE
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Use URI encoding as described in RFC 1808.
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The form is
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.Ql %dd
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where
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.Em d
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represents a hexadecimal digit.
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.It Dv VIS_OCTAL
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Use a three digit octal sequence. The form is
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.Ql \eddd
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where
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.Em d
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represents an octal digit.
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.El
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.Pp
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There is one additional flag,
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.Dv VIS_NOSLASH ,
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which inhibits the
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doubling of backslashes and the backslash before the default
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format (that is, control characters are represented by
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.Ql ^C
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and
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meta characters as
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.Ql M-C ) .
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With this flag set, the encoding is
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ambiguous and non-invertible.
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.Sh SEE ALSO
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.Xr unvis 1 ,
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.Xr unvis 3
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.Rs
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.%A R. Fielding
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.%T Relative Uniform Resource Locators
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.%O RFC1808
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.Re
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.Sh HISTORY
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These functions first appeared in
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.Bx 4.4 .
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