Terminal control/Clear the screen
You are encouraged to solve this task according to the task description, using any language you may know.
Clear the terminal window.
6502 Assembly
This example has been written for the C64 and uses the CHROUT KERNAL routine. Compile with the Turbo Macro Pro cross assembler:
tmpx -i clrscr.s -o bin/clrscr.prg
Run with:
SYS680
<lang 6502asm>; C64 - Terminal control: Clear the screen
- *** labels ***
chrout = $ffd2
- *** main ***
*=$02a8 ; sys 680 lda clr ; A = {CLR} jsr chrout ; Output a character in A to the current ; output device (default: screen). rts
- *** data ***
clr .byte $93 ; the CLR control code
; see https://en.wikipedia.org/wiki/PETSCII
</lang>
The 6502asm.com emulator has a 32x32 pixel screen. First we fill this screen with random colored pixels, wait for a keypress and then "clear" the screen (fill it with black pixels). <lang 6502asm>; 6502asm.com - Clear the screen
lda #$00 ; store the start address of the screen ($200) sta $00 ; at $00 and $01 (high byte in $01) lda #$02 sta $01 ldy #$00 ; Y = 0
fillscreen:
lda $fe ; A = random number from $fe sta ($00),y ; put pixel (random color) to the screen iny ; Y++ bne fillscreen ; loop if Y!=0 inc $01 ; increase address high byte lda $01 cmp #$06 ; A==6? (screen ends at $05ff) bne fillscreen ; no -> loop
waitforkeypress:
lda $ff ; $ff is 0 if no key has been pressed beq waitforkeypress ldx #$00 lda #$00 ; black
clearscreen:
sta $0200,x sta $0300,x sta $0400,x sta $0500,x inx bne clearscreen
</lang>
Ada
For systems with ANSI terminal handling:
<lang Ada>with Ada.Text_IO; procedure CLS is begin
Ada.Text_IO.Put(ASCII.ESC & "[2J");
end CLS;</lang>
AutoHotkey
Reference: http://www.autohotkey.com/forum/topic76532.html <lang AHK>RunWait %comspec% /c cls</lang>
AWK
<lang awk>system("clear")</lang>
Axe
<lang axe>ClrHome</lang>
BASIC
<lang qbasic>CLS</lang>
Applesoft BASIC
<lang ApplesoftBasic>HOME</lang>
BBC BASIC
<lang bbcbasic> CLS</lang> or <lang bbcbasic> VDU 12</lang> or <lang bbcbasic> PRINT CHR$(12);</lang>
GW-BASIC
<lang qbasic>10 CLS</lang>
PureBasic
Clears the whole console content using the current background color. <lang PureBasic>ClearConsole()</lang>
Batch File
<lang command>CLS</lang>
beeswax
Using the ANSI escape sequence Esc[2J
.
<lang beeswax>_3F..}`[2J`</lang>
Befunge
Assuming a terminal with support for ANSI escape sequences. <lang befunge>"J2["39*,,,,@</lang>
Blast
<lang blast>clear</lang>
Bracmat
<lang bracmat>sys$cls&</lang>
C
The C version of the Minesweeper game uses curses.
If perhaps clear screen isn't used, call the function cls
to do the trick.
<lang C>void cls(void) {
printf("\33[2J");
}</lang>
Here is the cheaty way no one likes, only works on Windows.
<lang C>#include <stdio.h>
- include <stdlib.h>
void main() {
printf ("clearing screen"); getchar(); system("cls");
}</lang>
C#
<lang csharp>System.Console.Clear();</lang>
COBOL
<lang cobol> PROGRAM-ID. blank-terminal.
DATA DIVISION. SCREEN SECTION. 01 blank-screen BLANK SCREEN. PROCEDURE DIVISION. DISPLAY blank-screen
GOBACK .</lang>
Comal
<lang Comal>PAGE</lang>
Common Lisp
<lang lisp> (format t "~C[2J" #\Esc) </lang> or it could be done passing the 'clear' command to the shell <lang lisp> (defun sh (cmd)
"A multi-implementation function equivalent for the C function system" #+clisp (shell cmd) #+ecl (si:system cmd) #+sbcl (sb-ext:run-program "/bin/sh" (list "-c" cmd) :input nil :output *standard-output*) #+clozure (ccl:run-program "/bin/sh" (list "-c" cmd) :input nil :output *standard-output*))
(sh "clear") </lang>
D
<lang d>extern (C) nothrow {
void disp_open(); void disp_move(int, int); void disp_eeop(); void disp_close();
}
void main() {
disp_open(); disp_move(0, 0); disp_eeop(); disp_close();
}</lang>
Erlang
<lang Erlang> clear()->io:format(os:cmd("clear")). </lang>
Euphoria
<lang Euphoria>clear_screen()</lang>
F#
<lang fsharp>open System
Console.Clear()</lang>
Forth
<lang forth>page</lang>
Fortran
Fortran 2008: <lang fortran>program clear
character(len=:), allocatable :: clear_command clear_command = "clear" !"cls" on Windows, "clear" on Linux and alike call execute_command_line(clear_command)
end program</lang>
Intel Fortran on Windows
Using console functions, one can also clear the screen without using a system command. See also Clearing the Screen on MSDN.
<lang fortran>program clear
use kernel32 implicit none integer(HANDLE) :: hStdout hStdout = GetStdHandle(STD_OUTPUT_HANDLE) call clear_console(hStdout)
contains
subroutine clear_console(hConsole) integer(HANDLE) :: hConsole type(T_COORD) :: coordScreen = T_COORD(0, 0) integer(DWORD) :: cCharsWritten type(T_CONSOLE_SCREEN_BUFFER_INFO) :: csbi integer(DWORD) :: dwConSize if (GetConsoleScreenBufferInfo(hConsole, csbi) == 0) return dwConSize = csbi%dwSize%X * csbi%dwSize%Y if (FillConsoleOutputCharacter(hConsole, SCHAR_" ", dwConSize, & coordScreen, loc(cCharsWritten)) == 0) return
if (GetConsoleScreenBufferInfo(hConsole, csbi) == 0) return if (FillConsoleOutputAttribute(hConsole, csbi%wAttributes, & dwConSize, coordScreen, loc(cCharsWritten)) == 0) return if (SetConsoleCursorPosition(hConsole, coordScreen) == 0) return end subroutine
end program</lang>
GNU Fortran on Windows
The preceding program can be compiled with GNU Fortran, with the following interface module for Windows API.
<lang fortran>module kernel32
use iso_c_binding implicit none integer, parameter :: HANDLE = C_INTPTR_T integer, parameter :: PVOID = C_INTPTR_T integer, parameter :: LPDWORD = C_INTPTR_T integer, parameter :: BOOL = C_INT integer, parameter :: SHORT = C_INT16_T integer, parameter :: WORD = C_INT16_T integer, parameter :: DWORD = C_INT32_T integer, parameter :: SCHAR = C_CHAR integer(DWORD), parameter :: STD_INPUT_HANDLE = -10 integer(DWORD), parameter :: STD_OUTPUT_HANDLE = -11 integer(DWORD), parameter :: STD_ERROR_HANDLE = -12
type, bind(C) :: T_COORD integer(SHORT) :: X, Y end type type, bind(C) :: T_SMALL_RECT integer(SHORT) :: Left integer(SHORT) :: Top integer(SHORT) :: Right integer(SHORT) :: Bottom end type
type, bind(C) :: T_CONSOLE_SCREEN_BUFFER_INFO type(T_COORD) :: dwSize type(T_COORD) :: dwCursorPosition integer(WORD) :: wAttributes type(T_SMALL_RECT) :: srWindow type(T_COORD) :: dwMaximumWindowSize end type
interface function FillConsoleOutputCharacter(hConsoleOutput, cCharacter, & nLength, dwWriteCoord, lpNumberOfCharsWritten) & bind(C, name="FillConsoleOutputCharacterA") import BOOL, C_CHAR, SCHAR, HANDLE, DWORD, T_COORD, LPDWORD !GCC$ ATTRIBUTES STDCALL :: FillConsoleOutputCharacter integer(BOOL) :: FillConsoleOutputCharacter integer(HANDLE), value :: hConsoleOutput character(kind=SCHAR), value :: cCharacter integer(DWORD), value :: nLength type(T_COORD), value :: dwWriteCoord integer(LPDWORD), value :: lpNumberOfCharsWritten end function end interface
interface function FillConsoleOutputAttribute(hConsoleOutput, wAttribute, & nLength, dwWriteCoord, lpNumberOfAttrsWritten) & bind(C, name="FillConsoleOutputAttribute") import BOOL, HANDLE, WORD, DWORD, T_COORD, LPDWORD !GCC$ ATTRIBUTES STDCALL :: FillConsoleOutputAttribute integer(BOOL) :: FillConsoleOutputAttribute integer(HANDLE), value :: hConsoleOutput integer(WORD), value :: wAttribute integer(DWORD), value :: nLength type(T_COORD), value :: dwWriteCoord integer(LPDWORD), value :: lpNumberOfAttrsWritten end function end interface interface function GetConsoleScreenBufferInfo(hConsoleOutput, & lpConsoleScreenBufferInfo) & bind(C, name="GetConsoleScreenBufferInfo") import BOOL, HANDLE, T_CONSOLE_SCREEN_BUFFER_INFO !GCC$ ATTRIBUTES STDCALL :: GetConsoleScreenBufferInfo integer(BOOL) :: GetConsoleScreenBufferInfo integer(HANDLE), value :: hConsoleOutput type(T_CONSOLE_SCREEN_BUFFER_INFO) :: lpConsoleScreenBufferInfo end function end interface interface function SetConsoleCursorPosition(hConsoleOutput, dwCursorPosition) & bind(C, name="SetConsoleCursorPosition") import BOOL, HANDLE, T_COORD !GCC$ ATTRIBUTES STDCALL :: SetConsoleCursorPosition integer(BOOL) :: SetConsoleCursorPosition integer(HANDLE), value :: hConsoleOutput type(T_COORD), value :: dwCursorPosition end function end interface interface function GetStdHandle(nStdHandle) bind(C, name="GetStdHandle") import HANDLE, DWORD !GCC$ ATTRIBUTES STDCALL :: GetStdHandle integer(HANDLE) :: GetStdHandle integer(DWORD), value :: nStdHandle end function end interface
end module </lang>
FreeBASIC
<lang freebasic>' FB 1.05.0 Win64
' FreeBASIC has a built in Cls command which clears the console on Windows ' but it may still be possible to scroll the console to view its ' previous contents. The following command prevents this.
Shell("Cls") Sleep</lang>
Go
External command
Probably most reliable way to clear the screen. <lang go>package main
import (
"os" "os/exec"
)
func main() {
c := exec.Command("clear") c.Stdout = os.Stdout c.Run()
}</lang>
ANSI escape code
Simplest, if your terminal supports the ANSI code you want. <lang go>package main
import "fmt"
func main() {
fmt.Print("\033[2J")
}</lang>
Ncurses
More complex, but works across multiple terminal types.
<lang go>package main
import (
"log" "time"
"code.google.com/p/goncurses"
)
func main() {
s, err := goncurses.Init() if err != nil { log.Fatal("goncurses:", err) } defer goncurses.End() s.Println("Clearing screen...") s.Refresh() time.Sleep(1 * time.Second)
s.Clear() // clear screen
// Goncurses saves the screen on Init and restores it on End. This // GetChar() allows you to see the effect of the program before it exits. s.GetChar() // press any key to continue
}</lang>
GUISS
This will only work if the terminal is sitting at a prompt. <lang guiss>Window:Terminal,Type:clear[enter]</lang>
Haskell
<lang Haskell> import System.Console.ANSI
main = clearScreen </lang>
Icon and Unicon
Example works for both Icon and Unicon. Determine which system command to call by querying &features at run time. Alternately, the related preprocessor symbols can be used to select the operating system. <lang Icon>procedure main ()
if &features == "MS Windows" then system("cls") # Windows else if &features == "UNIX" then system("clear") # Unix
end</lang>
J
Note: this is specific the java+gdi based J ide. <lang j>smwrite_jijs_ </lang>
Java
Using the ANSI escape sequence: <lang java>public class Clear {
public static void main (String[] args) { System.out.print("\033[2J"); }
}</lang> An alternative sequence: <lang java>public class Clear {
public static void main (String[] args) { System.out.print("\033\143"); }
}</lang>
jq
<lang jq>"\u001B[2J"</lang> Example: <lang sh>$ jq -n '"\u001B[2J"'</lang>
Kotlin
<lang scala>// version 1.1.2
fun main(args: Array<String>) {
println("\u001Bc") // Esc + c
}</lang>
Lasso
<lang Lasso>local( esc = decode_base64('Gw==') )
stdout(#esc + '[2J')</lang>
Logo
<lang logo>cleartext</lang> There is a separate command to reset the turtle graphics window. <lang logo>clearscreen cs ; abbreviation for clearscreen clean ; like cs, but doesn't reset turtle position</lang>
Lua
<lang lua>os.execute( "clear" )</lang> will not work because "clear" is not a command although you can use <lang lua>os.execute( "cls" )</lang>
Mathematica
Delegating to clear on terminal enabled OS(Mac Os, Linux) <lang Mathematica>Run["clear"];</lang>
Nemerle
Exactly as C#. Because of possible (probable) ambiguity, this is one time it may be prudent to use: <lang Nemerle>Console.Clear();</lang> rather than importing the Console class with using System.Console; and calling as: <lang Nemerle>Clear();</lang>
NewLISP
<lang NewLISP> (! "clear") </lang> In the newLISP command shell, this syntax is also proper: <lang NewLISP> !clear </lang>
Nim
<lang nim>import osproc discard execCmd "clear"</lang>
OCaml
Using the library ANSITerminal:
<lang ocaml>#load "unix.cma"
- directory "+ANSITerminal"
- load "ANSITerminal.cma"
open ANSITerminal
let () =
erase Screen</lang>
Octave
<lang Octave> system clear;</lang> <lang Octave> system('clear');</lang>
Pascal
<lang Pascal>clrscr;</lang>
Perl
Assuming some ANSI terminal, easiest way is call your system's clear command: <lang perl>system('clear')</lang>
If it's needed often: <lang perl>$clear = `clear`; # clear simply prints some escape sequence, cache it
- ... later:
print $clear;</lang>
We can also obtain the sequence using the Term::Cap module:
<lang perl>use Term::Cap;
$terminal = Term::Cap->Tgetent(); $clear = $terminal->Tputs('cl'); print $clear;</lang>
Perl 6
<lang perl6>sub clear { print state $ = qx[clear] } clear;</lang>
Phix
<lang Phix>clear_screen()</lang>
PicoLisp
<lang PicoLisp>(call 'clear)</lang>
PowerShell
<lang powershell>Clear-Host</lang>
ProDOS
<lang ProDOS>clearscurrentscreentext</lang>
Python
To clear the screen on Windows, replace 'clear' with 'cls'
<lang python>import os os.system("clear")</lang>
Or similar to C example (won't work in Winsows console, since it does not recognize ANSI sequences):
<lang python>print "\33[2J"</lang>
On Windows, using functions from the kernel32 DLL:
<lang python>from ctypes import *
STD_OUTPUT_HANDLE = -11
class COORD(Structure):
pass
COORD._fields_ = [("X", c_short), ("Y", c_short)]
class SMALL_RECT(Structure):
pass
SMALL_RECT._fields_ = [("Left", c_short), ("Top", c_short), ("Right", c_short), ("Bottom", c_short)]
class CONSOLE_SCREEN_BUFFER_INFO(Structure):
pass
CONSOLE_SCREEN_BUFFER_INFO._fields_ = [
("dwSize", COORD), ("dwCursorPosition", COORD), ("wAttributes", c_ushort), ("srWindow", SMALL_RECT), ("dwMaximumWindowSize", COORD)
]
def clear_console():
h = windll.kernel32.GetStdHandle(STD_OUTPUT_HANDLE)
csbi = CONSOLE_SCREEN_BUFFER_INFO() windll.kernel32.GetConsoleScreenBufferInfo(h, pointer(csbi)) dwConSize = csbi.dwSize.X * csbi.dwSize.Y
scr = COORD(0, 0) windll.kernel32.FillConsoleOutputCharacterA(h, c_char(b" "), dwConSize, scr, pointer(c_ulong())) windll.kernel32.FillConsoleOutputAttribute(h, csbi.wAttributes, dwConSize, scr, pointer(c_ulong())) windll.kernel32.SetConsoleCursorPosition(h, scr)
clear_console()</lang>
Racket
<lang racket>
- lang racket
(require (planet neil/charterm:3:0)) (with-charterm
(void (charterm-clear-screen)))
</lang>
Retro
<lang Retro>clear</lang>
REXX
generic
The REXX programming language does not include a facility to clear the screen natively.
However, it is possile to execute an external system command to achieve this task.
Below is some generic-type boilerplate (REXX) code which (possibly) determines:
- which REXX is being used
- which operating system is being used
- which (external) program to clear the screen
Also, not germane to this Rosetta Code task, the boilerplate code also possibly determines (among other things):
- if a particular documentation is to be shown
- which system pool name is to be used for system environmental variables
- which version of REXX is being used
- if the program is being invoked as a function, command, or subroutine
The following code works for:
- PC/REXX
- Personal REXX
- CMS REXX
- TSO REXX
- R4 REXX
- ROO REXX
- KEXX
- REXX compiler
- Regina REXX
The intent of the program's boilerplate code is to be able to be executed under most REXXes under most operating systems without changing the boilerplate REXX code.
<lang rexx>/*REXX boilerplate determines how to clear screen (under various REXXes)*/
trace off; parse arg ! /*turn off tracing; get C.L. args*/
if !all(arg()) then exit /*Doc request? Show, then exit.*/
if !cms then address /*Is this CMS? Use this address.*/
!cls /*clear the (terminal) screen. */ /* ◄═══ this is where "it" happens.*/
exit /*stick a fork in it, we're done.*/ /*═════════════════════════════general 1-line subs══════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════════*/ !all: !!=!;!=space(!);upper !;call !fid;!nt=right(!var('OS'),2)=='NT';!cls=word('CLS VMFCLEAR CLRSCREEN',1+!cms+!tso*2);if arg(1)\==1 then return 0;if wordpos(!,'? ?SAMPLES ?AUTHOR ?FLOW')==0 then return 0;!call=']$H';call '$H' !fn !;!call=;return 1 !cal: if symbol('!CALL')\=="VAR" then !call=; return !call !env: !env='ENVIRONMENT'; if !sys=='MSDOS'|!brexx|!r4|!roo then !env='SYSTEM'; if !os2 then !env='OS2'!env; !ebcdic=1=='f0'x; if !crx then !env='DOS'; return !fid: parse upper source !sys !fun !fid . 1 . . !fn !ft !fm .; call !sys; if !dos then do; _=lastpos('\',!fn); !fm=left(!fn,_); !fn=substr(!fn,_+1); parse var !fn !fn '.' !ft; end; return word(0 !fn !ft !fm,1+('0'arg(1))) !rex: parse upper version !ver !vernum !verdate .; !brexx='BY'==!vernum; !kexx='KEXX'==!ver; !pcrexx='REXX/PERSONAL'==!ver|'REXX/PC'==!ver; !r4='REXX-R4'==!ver; !regina='REXX-REGINA'==left(!ver,11); !roo='REXX-ROO'==!ver; call !env; return !sys: !cms=!sys=='CMS'; !os2=!sys=='OS2'; !tso=!sys=='TSO'|!sys=='MVS'; !vse=!sys=='VSE'; !dos=pos('DOS',!sys)\==0|pos('WIN',!sys)\==0|!sys=='CMD'; !crx=left(!sys,6)=='DOSCRX'; call !rex; return !var: call !fid; if !kexx then return space(dosenv(arg(1))); return space(value(arg(1),,!env))</lang>
Regina
The regina interpreter supports the rexxcurses plugin, which provides a facility to clear the screen (not shown here).
Scala
<lang Scala>object Cls extends App {print("\033[2J")}</lang>
Ring
<lang Ring>system('clear')</lang>
Ruby
<lang Ruby>system 'clear'</lang>
Or, without reliance on the command line:
(equivalent to `clear`
)
<lang Ruby>puts "\e[H\e[2J"</lang>
Seed7
The function clear is portable and clears the console window. Clear is based on terminfo respectively the Windows console API. A portable function to clear cannot rely on shell respectively cmd.exe commands, because Windows uses CLS and Unix shells use CLEAR, to clear a screen. ANSI terminal escape sequences are also not 100% portable, since not all terminals accept them.
<lang seed7>$ include "seed7_05.s7i";
include "console.s7i";
const proc: main is func
local var text: console is STD_NULL; begin console := open(CONSOLE); clear(console); # Terminal windows often restore the previous # content, when a program is terminated. Therefore # the program waits until Return/Enter is pressed. readln; end func;</lang>
Sidef
Using a cached-function: <lang ruby>func clear { print(static x = `clear`) }; clear();</lang>
Directly invoking the `clear` command: <lang ruby>Sys.run('clear');</lang>
Alternatively, without reliance on the command line: <lang ruby>print "\e[3J\e[H\e[2J";</lang>
Smalltalk
<lang smalltalk>Transcript clear.</lang>
Tcl
This only works on systems with ANSI terminal handling, i.e., Unix platforms. <lang tcl>puts -nonewline "\033\[2J" flush stdout</lang>
UNIX Shell
The clear command can be used to clear the terminal screen:
<lang bash>clear
- Alternative method using tput
tput clear</lang>
XPL0
<lang XPL0>code Clear=40; Clear;</lang>
zkl
<lang zkl>System.cmd(System.isWindows and "cls" or "clear"); // or, for ANSI terminals: print("\e[2J")</lang>
- Programming Tasks
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