201 lines
5.3 KiB
Groff
201 lines
5.3 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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.\" 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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.\" @(#)unvis.3 8.2 (Berkeley) 12/11/93
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.\" $FreeBSD$
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.\"
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.Dd December 11, 1993
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.Dt UNVIS 3
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.Os
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.Sh NAME
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.Nm unvis ,
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.Nm strunvis
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.Nd decode a visual representation of characters
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In vis.h
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.Ft int
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.Fn unvis "char *cp" "int c" "int *astate" "int flag"
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.Ft int
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.Fn strunvis "char *dst" "const char *src"
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.Ft int
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.Fn strunvisx "char *dst" "const char *src" "int flag"
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.Sh DESCRIPTION
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The
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.Fn unvis ,
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.Fn strunvis
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and
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.Fn strunvisx
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functions
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are used to decode a visual representation of characters, as produced
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by the
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.Xr vis 3
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function, back into
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the original form.
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Unvis is called with successive characters in
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.Fa c
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until a valid
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sequence is recognized, at which time the decoded character is
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available at the character pointed to by
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.Fa cp .
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Strunvis decodes the
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characters pointed to by
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.Fa src
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into the buffer pointed to by
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.Fa dst .
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.Pp
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The
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.Fn strunvis
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function
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simply copies
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.Fa src
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to
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.Fa dst ,
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decoding any escape sequences along the way,
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and returns the number of characters placed into
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.Fa dst ,
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or \-1 if an
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invalid escape sequence was detected.
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The size of
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.Fa dst
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should be
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equal to the size of
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.Fa src
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(that is, no expansion takes place during
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decoding).
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.Pp
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The
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.Fn strunvisx
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function does the same as the
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.Fn strunvis
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function,
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but it allows you to add a flag that specifies the style the string
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.Fa src
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is encoded with.
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Currently, the only supported flag is
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.Dv VIS_HTTPSTYLE .
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.Pp
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The
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.Fn unvis
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function
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implements a state machine that can be used to decode an arbitrary
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stream of bytes.
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All state associated with the bytes being decoded
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is stored outside the
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.Fn unvis
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function (that is, a pointer to the state is passed in), so
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calls decoding different streams can be freely intermixed.
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To
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start decoding a stream of bytes, first initialize an integer
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to zero.
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Call
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.Fn unvis
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with each successive byte, along with a pointer
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to this integer, and a pointer to a destination character.
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The
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.Fn unvis
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function
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has several return codes that must be handled properly.
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They are:
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.Bl -tag -width UNVIS_VALIDPUSH
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.It Li \&0 (zero)
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Another character is necessary; nothing has been recognized yet.
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.It Dv UNVIS_VALID
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A valid character has been recognized and is available at the location
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pointed to by cp.
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.It Dv UNVIS_VALIDPUSH
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A valid character has been recognized and is available at the location
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pointed to by cp; however, the character currently passed in should
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be passed in again.
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.It Dv UNVIS_NOCHAR
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A valid sequence was detected, but no character was produced.
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This
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return code is necessary to indicate a logical break between characters.
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.It Dv UNVIS_SYNBAD
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An invalid escape sequence was detected, or the decoder is in an
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unknown state.
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The decoder is placed into the starting state.
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.El
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.Pp
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When all bytes in the stream have been processed, call
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.Fn unvis
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one more time with
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.Fa flag
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set to
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.Dv UNVIS_END
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to extract any remaining character (the character passed in is ignored).
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.Pp
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The
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.Fa flag
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argument is also used to specify the encoding style of the source.
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If set to
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.Dv VIS_HTTPSTYLE ,
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.Fn unvis
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will decode URI strings as specified in RFC 1808.
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.Pp
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The following code fragment illustrates a proper use of
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.Fn unvis .
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.Bd -literal -offset indent
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int state = 0;
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char out;
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while ((ch = getchar()) != EOF) {
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again:
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switch(unvis(&out, ch, &state, 0)) {
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case 0:
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case UNVIS_NOCHAR:
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break;
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case UNVIS_VALID:
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(void) putchar(out);
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break;
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case UNVIS_VALIDPUSH:
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(void) putchar(out);
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goto again;
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case UNVIS_SYNBAD:
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(void)fprintf(stderr, "bad sequence!\en");
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exit(1);
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}
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}
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if (unvis(&out, (char)0, &state, UNVIS_END) == UNVIS_VALID)
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(void) putchar(out);
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.Ed
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.Sh SEE ALSO
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.Xr vis 1 ,
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.Xr vis 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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The
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.Fn unvis
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function
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first appeared in
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.Bx 4.4 .
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