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.\" Copyright (c) 1989, 1991, 1993, 1994
.\" The Regents of the University of California. All rights reserved.
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.\" modification, are permitted provided that the following conditions
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.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
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.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgement:
.\" This product includes software developed by the University of
.\" California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
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.\"
.\" @(#)vis.1 8.4 (Berkeley) 4/19/94
.\" $FreeBSD$
.\"
.Dd June 25, 2004
.Dt VIS 1
.Os
.Sh NAME
.Nm vis
.Nd display non-printable characters in a visual format
.Sh SYNOPSIS
.Nm
.Op Fl cbflnostw
.Op Fl F Ar foldwidth
.Op Ar
.Sh DESCRIPTION
The
.Nm
utility is a filter for converting non-printable characters
into a visual representation.
It differs from
.Ql 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
.Xr vis 3 .
.Pp
The options are as follows:
.Bl -tag -width indent
.It Fl 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
.Dq Li cat -v .
.It Fl c
Request a format which displays a small subset of the
non-printable characters using C-style backslash sequences.
.It Fl F
Causes
.Nm
to fold output lines to
.Ar foldwidth
columns (default 80), like
.Xr fold 1 ,
except
that a hidden newline sequence is used (which is removed
when inverting the file back to its original form with
.Xr 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 do not work with partial lines.
.It Fl f
Same as
.Fl F .
.It Fl l
Mark newlines with the visible sequence
.Ql \e$ ,
followed by the newline.
.It Fl n
Turns off any encoding, except for the fact that backslashes are
still doubled and hidden newline sequences inserted if
.Fl f
or
.Fl F
is selected.
When combined with the
.Fl f
flag,
.Nm
becomes like
an invertible version of the
.Xr fold 1
utility.
That is, the output
can be unfolded by running the output through
.Xr unvis 1 .
.It Fl o
Request a format which displays non-printable characters as
an octal number, \eddd.
.It Fl s
Only characters considered unsafe to send to a terminal are encoded.
This flag allows backspace, bell, and carriage return in addition
to the default space, tab and newline.
.It Fl t
Tabs are also encoded.
.It Fl w
White space (space-tab-newline) is also encoded.
.El
.Sh SEE ALSO
.Xr unvis 1 ,
.Xr vis 3
.Sh HISTORY
The
.Nm
command appeared in
.Bx 4.4 .
.Sh BUGS
Due to limitations in the underlying
.Xr vis 3
function, the
.Nm
utility
does not recognize multibyte characters, and thus may consider them to be
non-printable when they are in fact printable (and vice versa).
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