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28 .\"
29 .\" $Id: clear.1,v 1.18 2017/10/07 21:30:17 tom Exp $
30 .TH clear 1 ""
31 .\" these would be fallbacks for DS/DE,
32 .\" but groff changed the meaning of the macros.
33 .de NS
34 .ie \n(.sp
35 .el .sp .5
36 .ie \n(.in +4
37 .el .in +2
38 .nf
39 .ft C \" Courier
40 ..
41 .de NE
42 .fi
43 .ft R
44 .in -4
45 ..
46 .ie \n(.g .ds `` \(lq
47 .el .ds `` ``
48 .ie \n(.g .ds '' \(rq
49 .el .ds '' ''
50 .de bP
51 .IP \(bu 4
52 ..
53 .ds n 5
54 .SH NAME
55 \fBclear\fR \- clear the terminal screen
56 .SH SYNOPSIS
57 \fBclear\fR [\fB\-T\fR\fItype\fR] [\fB\-V\fP] [\fB\-x\fP]
58 .br
59 .SH DESCRIPTION
60 \fBclear\fR clears your screen if this is possible,
61 including its scrollback buffer (if the extended \*(``E3\*('' capability is defined).
62 \fBclear\fR looks in the environment for the terminal type
63 given by the environment variable \fBTERM\fP,
64 and then in the
65 \fBterminfo\fR database to determine how to clear the screen.
66 .PP
67 \fBclear\fR writes to the standard output.
68 You can redirect the standard output to a file (which prevents
69 \fBclear\fR from actually clearing the screen),
70 and later \fBcat\fP the file to the screen, clearing it at that point.
71 .SH OPTIONS
72 .PP
73 .TP 5
74 .B \-T \fItype\fP
75 indicates the \fItype\fR of terminal.
76 Normally this option is
77 unnecessary, because the default is taken from the environment
78 variable \fBTERM\fR.
79 If \fB\-T\fR is specified, then the shell
80 variables \fBLINES\fR and \fBCOLUMNS\fR will also be ignored.
81 .TP
82 .B \-V
83 reports the version of ncurses which was used in this program, and exits.
84 The options are as follows:
85 .TP
86 .B \-x
87 do not attempt to clear the terminal's scrollback buffer
88 using the extended \*(``E3\*('' capability.
89 .SH HISTORY
90 A \fBclear\fP command appeared in 2.79BSD dated February 24, 1979.
91 Later that was provided in Unix 8th edition (1985).
92 .PP
93 AT&T adapted a different BSD program (\fBtset\fP) to make
94 a new command (\fBtput\fP),
95 and used this to replace the \fBclear\fP command with a shell script
96 which calls \fBtput clear\fP, e.g.,
97 .NS
98 /usr/bin/tput ${1:+-T$1} clear 2> /dev/null
99 exit
100 .NE
101 .PP
102 In 1989, when Keith Bostic revised the BSD \fBtput\fP command
103 to make it similar to the AT&T \fBtput\fP,
104 he added a shell script for the \fBclear\fP command:
105 .NS
106 exec tput clear
107 .NE
108 .PP
109 The remainder of the script in each case is a copyright notice.
110 .PP
111 The ncurses \fBclear\fP command began in 1995 by adapting the original
112 BSD \fBclear\fP command (with terminfo, of course).
113 .PP
114 The \fBE3\fP extension came later:
115 .bP
116 In June 1999, xterm provided an extension to the standard control
117 sequence for clearing the screen.
118 Rather than clearing just the visible part of the screen using
119 .NS
120 printf '\\033[2J'
121 .NE
122 .IP
123 one could clear the \fIscrollback\fP using
124 .NS
125 printf '\\033[\fB3\fPJ'
126 .NE
127 .IP
128 This is documented in \fIXTerm Control Sequences\fP as a feature originating
129 with xterm.
130 .bP
131 A few other terminal developers adopted the feature, e.g., PuTTY in 2006.
132 .bP
133 In April 2011, a Red Hat developer submitted a patch to the Linux
134 kernel, modifying its console driver to do the same thing.
135 The Linux change, part of the 3.0 release, did not mention xterm,
136 although it was cited in the Red Hat bug report (#683733)
137 which led to the change.
138 .bP
139 Again, a few other terminal developers adopted the feature. But the
140 next relevant step was a change to the \fBclear\fP program in 2013
141 to incorporate this extension.
142 .bP
143 In 2013, the \fBE3\fP extension was overlooked in \fBtput\fP with
144 the \*(``clear\*('' parameter.
145 That was addressed in 2016 by reorganizing \fBtput\fP to share
146 its logic with \fBclear\fP and \fBtset\fP.
147 .SH PORTABILITY
148 Neither IEEE Std 1003.1/The Open Group Base Specifications Issue 7
149 (POSIX.1-2008) nor X/Open Curses Issue 7 documents tset or reset.
150 .PP
151 The latter documents \fBtput\fP, which could be used to replace this utility
152 either via a shell script or by an alias (such as a symbolic link) to
153 run \fBtput\fP as \fBclear\fP.
154 .SH SEE ALSO
155 \fBtput\fR(1), \fBterminfo\fR(\*n)
156 .PP
157 This describes \fBncurses\fR
158 version 6.0 (patch 20171007).