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.\"     @(#)vis.1	8.4 (Berkeley) 4/19/94
.\"
.Dd February 13, 2013
.Dt VIS 1
.Os
.Sh NAME
.Nm vis
.Nd display non-printable characters in a visual format
.Sh SYNOPSIS
.Nm
.Op Fl bcfhlmnostw
.Op Fl e Ar extra
.Op Fl F Ar foldwidth
.Op Ar file ...
.Sh DESCRIPTION
.Nm
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 Ds
.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 .
.Pq Dv VIS_NOSLASH
.It Fl c
Request a format which displays a small subset of the
non-printable characters using C-style backslash sequences.
.Pq Dv VIS_CSTYLE
.It Fl e Ar extra
Also encode characters in
.Ar extra ,
per
.Xr svis 3 .
.It Fl F Ar foldwidth
Causes
.Nm
to fold output lines to 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 don't work with partial lines.
.It Fl f
Same as
.Fl F .
.It Fl h
Encode using the URI encoding from RFC 1808.
.Pq Dv VIS_HTTPSTYLE
.It Fl l
Mark newlines with the visible sequence
.Ql \e$ ,
followed by the newline.
.It Fl m
Encode using the MIME Quoted-Printable encoding from RFC 2045.
.Pq Dv VIS_MIMESTYLE
.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.
.Pq Dv VIS_OCTAL
.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.
.Pq Dv VIS_SAFE
.It Fl t
Tabs are also encoded.
.Pq Dv VIS_TAB
.It Fl w
White space (space-tab-newline) is also encoded.
.Pq Dv VIS_WHITE
.El
.Sh MULTIBYTE CHARACTER SUPPORT
.Nm
supports multibyte character input.
The encoding conversion is influenced by the setting of the
.Ev LC_CTYPE
environment variable which defines the set of characters that can be
copied without encoding.
.Pp
When 8-bit data is present in the input,
.Ev LC_CTYPE
must be set to the correct locale or to the C locale.
If the locales of the data and the conversion are mismatched, multibyte
character recognition may fail and encoding will be performed byte-by-byte
instead.
.Sh ENVIRONMENT
.Bl -tag -width ".Ev LC_CTYPE"
.It Ev LC_CTYPE
Specify the locale of the input data.
Set to C if the input data locale is unknown.
.Sh SEE ALSO
.Xr unvis 1 ,
.Xr svis 3 ,
.Xr vis 3
.Sh HISTORY
The
.Nm
command appears in
.Bx 4.4 .
Myltibyte character support was added in
.Nx 6.1
and
.Fx 9.2 .