Execute a system command
You are encouraged to solve this task according to the task description, using any language you may know.
- Task
Run either the ls system command (dir on Windows), or the pause system command.
- Related task
11l
os:(‘pause’)
ABAP
ABAP report which checks if there is an external command called 'ls' for the os of the current application server. When running on Windows, it calls dir, for all other platforms ls. A new command is created if not existing and run.
*&---------------------------------------------------------------------*
*& Report ZEXEC_SYS_CMD
*&
*&---------------------------------------------------------------------*
*&
*&
*&---------------------------------------------------------------------*
REPORT zexec_sys_cmd.
DATA: lv_opsys TYPE syst-opsys,
lt_sxpgcotabe TYPE TABLE OF sxpgcotabe,
ls_sxpgcotabe LIKE LINE OF lt_sxpgcotabe,
ls_sxpgcolist TYPE sxpgcolist,
lv_name TYPE sxpgcotabe-name,
lv_opcommand TYPE sxpgcotabe-opcommand,
lv_index TYPE c,
lt_btcxpm TYPE TABLE OF btcxpm,
ls_btcxpm LIKE LINE OF lt_btcxpm
.
* Initialize
lv_opsys = sy-opsys.
CLEAR lt_sxpgcotabe[].
IF lv_opsys EQ 'Windows NT'.
lv_opcommand = 'dir'.
ELSE.
lv_opcommand = 'ls'.
ENDIF.
* Check commands
SELECT * FROM sxpgcotabe INTO TABLE lt_sxpgcotabe
WHERE opsystem EQ lv_opsys
AND opcommand EQ lv_opcommand.
IF lt_sxpgcotabe IS INITIAL.
CLEAR ls_sxpgcolist.
CLEAR lv_name.
WHILE lv_name IS INITIAL.
* Don't mess with other users' commands
lv_index = sy-index.
CONCATENATE 'ZLS' lv_index INTO lv_name.
SELECT * FROM sxpgcostab INTO ls_sxpgcotabe
WHERE name EQ lv_name.
ENDSELECT.
IF sy-subrc = 0.
CLEAR lv_name.
ENDIF.
ENDWHILE.
ls_sxpgcolist-name = lv_name.
ls_sxpgcolist-opsystem = lv_opsys.
ls_sxpgcolist-opcommand = lv_opcommand.
* Create own ls command when nothing is declared
CALL FUNCTION 'SXPG_COMMAND_INSERT'
EXPORTING
command = ls_sxpgcolist
public = 'X'
EXCEPTIONS
command_already_exists = 1
no_permission = 2
parameters_wrong = 3
foreign_lock = 4
system_failure = 5
OTHERS = 6.
IF sy-subrc <> 0.
* Implement suitable error handling here
ELSE.
* Hooray it worked! Let's try to call it
CALL FUNCTION 'SXPG_COMMAND_EXECUTE_LONG'
EXPORTING
commandname = lv_name
TABLES
exec_protocol = lt_btcxpm
EXCEPTIONS
no_permission = 1
command_not_found = 2
parameters_too_long = 3
security_risk = 4
wrong_check_call_interface = 5
program_start_error = 6
program_termination_error = 7
x_error = 8
parameter_expected = 9
too_many_parameters = 10
illegal_command = 11
wrong_asynchronous_parameters = 12
cant_enq_tbtco_entry = 13
jobcount_generation_error = 14
OTHERS = 15.
IF sy-subrc <> 0.
* Implement suitable error handling here
WRITE: 'Cant execute ls - '.
CASE sy-subrc.
WHEN 1.
WRITE: / ' no permission!'.
WHEN 2.
WRITE: / ' command could not be created!'.
WHEN 3.
WRITE: / ' parameter list too long!'.
WHEN 4.
WRITE: / ' security risk!'.
WHEN 5.
WRITE: / ' wrong call of SXPG_COMMAND_EXECUTE_LONG!'.
WHEN 6.
WRITE: / ' command cant be started!'.
WHEN 7.
WRITE: / ' program terminated!'.
WHEN 8.
WRITE: / ' x_error!'.
WHEN 9.
WRITE: / ' parameter missing!'.
WHEN 10.
WRITE: / ' too many parameters!'.
WHEN 11.
WRITE: / ' illegal command!'.
WHEN 12.
WRITE: / ' wrong asynchronous parameters!'.
WHEN 13.
WRITE: / ' cant enqueue job!'.
WHEN 14.
WRITE: / ' cant create job!'.
WHEN 15.
WRITE: / ' unknown error!'.
WHEN OTHERS.
WRITE: / ' unknown error!'.
ENDCASE.
ELSE.
LOOP AT lt_btcxpm INTO ls_btcxpm.
WRITE: / ls_btcxpm.
ENDLOOP.
ENDIF.
ENDIF.
ENDIF.
Ada
Using the IEEE POSIX Ada standard, P1003.5c:
with POSIX.Unsafe_Process_Primitives;
procedure Execute_A_System_Command is
Arguments : POSIX.POSIX_String_List;
begin
POSIX.Append (Arguments, "ls");
POSIX.Unsafe_Process_Primitives.Exec_Search ("ls", Arguments);
end Execute_A_System_Command;
Importing the C system() function:
with Interfaces.C; use Interfaces.C;
procedure Execute_System is
function Sys (Arg : Char_Array) return Integer;
pragma Import(C, Sys, "system");
Ret_Val : Integer;
begin
Ret_Val := Sys(To_C("ls"));
end Execute_System;
Using the GNAT run-time library:
with Ada.Text_IO; use Ada.Text_IO;
with System.OS_Lib; use System.OS_Lib;
procedure Execute_Synchronously is
Result : Integer;
Arguments : Argument_List :=
( 1=> new String'("cmd.exe"),
2=> new String'("/C dir c:\temp\*.adb")
);
begin
Spawn
( Program_Name => "cmd.exe",
Args => Arguments,
Output_File_Descriptor => Standout,
Return_Code => Result
);
for Index in Arguments'Range loop
Free (Arguments (Index)); -- Free the argument list
end loop;
end Execute_Synchronously;
Aikido
The simplest way to do this is using the system()
function. It returns a vector of strings (the output from the command).
var lines = system ("ls")
foreach line lines {
println (line)
}
If you don't want to process the output you can use the exec
function. It writes the output to the standard output stream by default;
exec ("ls")
You also have the regular fork
and execv
calls available:
var pid = fork()
if (pid == 0) {
var args = ["/bin/ls"]
execv ("/bin/ls", args)
exit(1)
}
var status = 0
waitpid (pid, status)
Aime
sshell ss;
ss.argv.insert("ls");
o_(ss.link);
ALGOL 68
system("ls")
Or the classic "!" shell escape can be implemented as an "!" operator:
OP ! = (STRING cmd)BOOL: system(cmd) = 0;
IF ! "touch test.tmp" ANDF ( ! "ls test.tmp" ANDF ! "rm test.tmp" ) THEN
print (("test.tmp now gone!", new line))
FI
Amazing Hopper
#!/usr/bin/hopper
#include <hopper.h>
main:
/* execute "ls -lstar" with no result return (only displayed) */
{"ls -lstar"},execv
/* this form does not allow composition of the line with variables.
Save result in the variable "s", and then display it */
s=`ls -l | awk '{if($2=="2")print $0;}'`
{"\n",s,"\n"}print
data="2"
{""}tok sep
// the same as above, only I can compose the line:
{"ls -l | awk '{if($2==\"",data,"\")print $0;}'"}join(s),{s}exec,print
{"\n\n"}print
// this does the same as above, with an "execute" macro inside a "let" macro:
t=0,let (t := execute( {"ls -l | awk '{if($2==\""},{data},{"\")print $0;}'"} ))
{t,"\n"}print
{0}return
APL
∇ system s;handle
⍝⍝ NOTE: one MUST give the full absolute path to the program (eg. /bin/ls)
⍝⍝ Exercise: Can you improve this by parsing the value of
⍝⍝ ⎕ENV 'PATH' ?
⍝⍝
handle ← ⎕fio['fork_daemon'] s
⎕fio['fclose'] handle
∇
system '/bin/ls /var'
backups games lib lock mail run tmp
cache gemini local log opt spool
AppleScript
do shell script "ls" without altering line endings
Applesoft BASIC
? CHR$(4)"CATALOG"
Arturo
print execute "ls"
AutoHotkey
Run, %comspec% /k dir & pause
AutoIt
Run(@ComSpec & " /c " & 'pause', "", @SW_HIDE)
AWK
Using system() function:
BEGIN {
system("ls") # Unix
#system("dir") # DOS/MS-Windows
}
Using getline command:
BEGIN {
ls = sys2var("ls")
print ls
}
function sys2var(command ,fish, scale, ship) {
command = command " 2>/dev/null"
while ( (command | getline fish) > 0 ) {
if ( ++scale == 1 )
ship = fish
else
ship = ship "\n" fish
}
close(command)
return ship
}
BASIC
SHELL "dir"
BaCon
' Execute a system command
SYSTEM "ls"
BASIC256
system "dir"
Batch File
dir
BBC BASIC
On Acorn computers the *CAT command catalogues the current directory, the equivalent of the Unix ls command or the DOS/Windows dir command. The BBC BASIC OSCLI command passes a string to the Command Line Interpreter to execute a system command, it is the equivalent of C's system() command.
OSCLI "CAT"
With BBC BASIC for Windows you can execute the Windows dir command:
OSCLI "*dir":REM *dir to bypass BB4W's built-in dir command
And if running BBC BASIC on a Unix host, you can execute the ls command:
OSCLI "ls"
Befunge
Works with any Funge-98 on Unix, try https://tio.run/##S0pNK81LT9W1tNAtqAQz//9XKs5RsnX4/x8A
"sl"=@;pushes ls, = executes it, @ ends it;
BQN
•SH
is a function defined in the BQN spec, which provides output from a shell command.
The arguments to •SH
are the command, followed by its arguments as a flat list of strings. For example:
•SH ⟨"ls"⟩
Will give an output as a list of three elements: the command's exit code, text written to stdout, and text written to stderr.
Bracmat
sys$dir
Brat
include :subprocess
p subprocess.run :ls #Lists files in directory
Brlcad
exec ls
C
ISO C & POSIX:
#include <stdlib.h>
int main()
{
system("ls");
return 0;
}
C#
Using Windows / .NET:
using System.Diagnostics;
namespace Execute
{
class Program
{
static void Main(string[] args)
{
Process.Start("cmd.exe", "/c dir");
}
}
}
using System;
class Execute {
static void Main() {
System.Diagnostics.Process proc = new System.Diagnostics.Process();
proc.EnableRaisingEvents=false;
proc.StartInfo.FileName="ls";
proc.Start();
}
}
C++
system("pause");
Clojure
(.. Runtime getRuntime (exec "cmd /C dir"))
user=> (use '[clojure.java.shell :only [sh]])
user=> (sh "ls" "-aul")
{:exit 0,
:out total 64
drwxr-xr-x 11 zkim staff 374 Jul 5 13:21 .
drwxr-xr-x 25 zkim staff 850 Jul 5 13:02 ..
drwxr-xr-x 12 zkim staff 408 Jul 5 13:02 .git
-rw-r--r-- 1 zkim staff 13 Jul 5 13:02 .gitignore
-rw-r--r-- 1 zkim staff 12638 Jul 5 13:02 LICENSE.html
-rw-r--r-- 1 zkim staff 4092 Jul 5 13:02 README.md
drwxr-xr-x 2 zkim staff 68 Jul 5 13:15 classes
drwxr-xr-x 5 zkim staff 170 Jul 5 13:15 lib
-rw-r--r--@ 1 zkim staff 3396 Jul 5 13:03 pom.xml
-rw-r--r--@ 1 zkim staff 367 Jul 5 13:15 project.clj
drwxr-xr-x 4 zkim staff 136 Jul 5 13:15 src
, :err }
user=> (use '[clojure.java.shell :only [sh]])
user=> (println (:out (sh "cowsay" "Printing a command-line output")))
_________________________________
< Printing a command-line output. >
---------------------------------
\ ^__^
\ (oo)\_______
(__)\ )\/\
||----w |
|| ||
nil
CMake
execute_process(COMMAND ls)
Because of a quirk in the implementation (cmExecuteProcessCommand.cxx and ProcessUNIX.c), CMake diverts the standard output to a pipe. The effect is like running ls | cat
in the shell. The ls process inherits the original standard input and standard error, but receives a new pipe for standard output. CMake then reads this pipe and copies all data to the original standard output.
execute_process() can also chain commands in a pipeeline, and capture output.
# Calculate pi to 40 digits after the decimal point.
execute_process(
COMMAND printf "scale = 45; 4 * a(1) + 5 / 10 ^ 41\\n"
COMMAND bc -l
COMMAND sed -e "s/.\\{5\\}$//"
OUTPUT_VARIABLE pi OUTPUT_STRIP_TRAILING_WHITESPACE)
message(STATUS "pi is ${pi}")
-- pi is 3.1415926535897932384626433832795028841972
COBOL
CALL "SYSTEM" USING BY CONTENT "ls"
CoffeeScript
{ spawn } = require 'child_process'
ls = spawn 'ls'
ls.stdout.on 'data', ( data ) -> console.log "Output: #{ data }"
ls.stderr.on 'data', ( data ) -> console.error "Error: #{ data }"
ls.on 'close', -> console.log "'ls' has finished executing."
Common Lisp
(with-output-to-string (stream) (extensions:run-program "ls" nil :output stream))
(system:call-system "ls")
(trivial-shell:shell-command "ls")
; uiop is part of the de facto build system, asdf, so should be available to most installations.
; synchronous
(uiop:run-program "ls")
; async
(defparameter *process* (uiop:launch-program "ls"))
(uiop:wait-process *process*)
D
import std.process, std.stdio;
//these two alternatives wait for the process to return, and capture the output
//each process function returns a Tuple of (int)"status" and (string)"output
auto ls_string = executeShell("ls -l"); //takes single string
writeln((ls_string.status == 0) ? ls_string.output : "command failed");
auto ls_array = execute(["ls", "-l"]); //takes array of strings
writeln((ls_array.status == 0) ? ls_array.output : "command failed");
//other alternatives exist to spawn processes in parallel and capture output via pipes
std.process.system() is deprecated.
dc
! ls
DBL
XCALL SPAWN ("ls *.jpg > file.txt") ;execute command and continue
XCALL EXEC ("script.sh") ;execute script or binary and exit
STOP '@/bin/ls *.jpg > file.txt' ;exit and execute command
DCL
Directory
Or, shorter
dir
Delphi
program ExecuteSystemCommand;
{$APPTYPE CONSOLE}
uses Windows, ShellApi;
begin
ShellExecute(0, nil, 'cmd.exe', ' /c dir', nil, SW_HIDE);
end.
E
def ls := makeCommand("ls")
ls("-l")
def [results, _, _] := ls.exec(["-l"])
when (results) -> {
def [exitCode, out, err] := results
print(out)
} catch problem {
print(`failed to execute ls: $problem`)
}
Emacs Lisp
Synchronously (shell, interactive):
(shell-command "ls")
Asynchronously (shell, interactive):
(async-shell-command "ls")
Erlang
os:cmd("ls").
ERRE
In ERRE language you have the SHELL command followed, eventually, by a string command. SHELL itself opens a new DOS/Windows shell: you must use EXIT to end. For example
SHELL("DIR/W")
lists the current directory and then returns to the program.
cmd$="DIR/W"
SHELL(cmd$)
Euphoria
Euphoria has 2 systems command functions: system() and system_exec().
-- system --
-- the simplest way --
-- system spawns a new shell so I/O redirection is possible --
system( "dir /w c:\temp\ " ) -- Microsoft --
system( "/bin/ls -l /tmp" ) -- Linux BSD OSX --
----
-- system_exec() --
-- system_exec does not spawn a new shell --
-- ( like bash or cmd.exe ) --
integer exit_code = 0
sequence ls_command = ""
ifdef UNIX or LINUX or OSX then
ls_command = "/bin/ls -l "
elsifdef WINDOWS then
ls_command = "dir /w "
end ifdef
exit_code = system_exec( ls_command )
if exit_code = -1 then
puts( STDERR, " could not execute " & ls_command & "\n" )
elsif exit_code = 0 then
puts( STDERR, ls_command & " succeeded\n")
else
printf( STDERR, "command %s failed with code %d\n", ls_command, exit_code)
end if
F#
System.Diagnostics.Process.Start("cmd", "/c dir")
Factor
"ls" run-process wait-for-process
Fantom
The Process class handles creating and running external processes. in/out/err streams can be redirected, but default to the usual stdin/stdout/stderr. So following program prints result of 'ls' to the command line:
class Main
{
public static Void main ()
{
p := Process (["ls"])
p.run
}
}
Forth
s" ls" system
Fortran
execute_command_line subroutine in Fortran 2008 and later runs a system command
program SystemTest
integer :: i
call execute_command_line ("ls", exitstat=i)
end program SystemTest
The SYSTEM subroutine (and function) are a GNU extension.
program SystemTest
call system("ls")
end program SystemTest
FreeBASIC
' FB 1.05.0 Win64
Shell "dir"
Sleep
Frink
r = callJava["java.lang.Runtime", "getRuntime"]
println[read[r.exec["dir"].getInputStream[]]]
FunL
import sys.execute
execute( if $os.startsWith('Windows') then 'dir' else 'ls' )
FutureBasic
FB 7.0.23+
print unix(@"ls -A")
Classic FB using Pascal strings
local fn DoUnixCommand( cmd as str255 )
str255 s
open "Unix", 2, cmd
while ( not eof(2) )
line input #2, s
print s
wend
close 2
end fn
fn DoUnixCommand( "ls -A" )
Output:
.DocumentRevisions-V100 .Spotlight-V100 .Trashes .file .fseventsd .hotfiles.btree .vol Applications Library Network System Users Volumes bin cores dev etc home mach_kernel net private sbin tmp usr var
Modern FB using CFStrings
include "NSLog.incl"
// For remote uses like curl
// #plist NSAppTransportSecurity @{NSAllowsArbitraryLoads:YES}
local fn RunTerminalCommand( cmd as CFStringRef ) as CFStringRef
————————————————————————————————————————————————————————————————————————————————————————————————————
ErrorRef err = NULL
CFStringRef outputStr = NULL
TaskRef task = fn TaskInit
TaskSetExecutableURL( task, fn URLFileURLWithPath( @"/bin/zsh" ) )
CFStringRef cmdStr = fn StringWithFormat( @"%@", cmd )
CFArrayRef args = fn ArrayWithObjects( @"-c", cmdStr, NULL )
TaskSetArguments( task, args )
PipeRef p = fn PipeInit
TaskSetStandardOutput( task, p )
TaskSetStandardError( task, p )
FileHandleRef fh = fn PipeFileHandleForReading( p )
fn TaskLaunch( task, NULL )
TaskWaitUntilExit( task )
CFDataRef dta = fn FileHandleReadDataToEndOfFile( fh, @err )
if err then NSLog( @"Error reading file: %@", fn ErrorLocalizedDescription( err ) ) : exit fn
fn FileHandleClose( fh, @err )
if err then NSLog( @"Error closing file: %@", fn ErrorLocalizedDescription( err ) ) : exit fn
outputStr = fn StringWithData( dta, NSUTF8StringEncoding )
end fn = outputStr
CFStringRef cmd
cmd = @"cal 2023"
NSLog( @"%@", fn RunTerminalCommand( cmd ) )
HandleEvents
- Output:
2023 January February March Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa 1 2 3 4 5 6 7 1 2 3 4 1 2 3 4 8 9 10 11 12 13 14 5 6 7 8 9 10 11 5 6 7 8 9 10 11 15 16 17 18 19 20 21 12 13 14 15 16 17 18 12 13 14 15 16 17 18 22 23 24 25 26 27 28 19 20 21 22 23 24 25 19 20 21 22 23 24 25 29 30 31 26 27 28 26 27 28 29 30 31 April May June Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa 1 1 2 3 4 5 6 1 2 3 2 3 4 5 6 7 8 7 8 9 10 11 12 13 4 5 6 7 8 9 10 9 10 11 12 13 14 15 14 15 16 17 18 19 20 11 12 13 14 15 16 17 16 17 18 19 20 21 22 21 22 23 24 25 26 27 18 19 20 21 22 23 24 23 24 25 26 27 28 29 28 29 30 31 25 26 27 28 29 30 30 July August September Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa 1 1 2 3 4 5 1 2 2 3 4 5 6 7 8 6 7 8 9 10 11 12 3 4 5 6 7 8 9 9 10 11 12 13 14 15 13 14 15 16 17 18 19 10 11 12 13 14 15 16 16 17 18 19 20 21 22 20 21 22 23 24 25 26 17 18 19 20 21 22 23 23 24 25 26 27 28 29 27 28 29 30 31 24 25 26 27 28 29 30 30 31 October November December Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa 1 2 3 4 5 6 7 1 2 3 4 1 2 8 9 10 11 12 13 14 5 6 7 8 9 10 11 3 4 5 6 7 8 9 15 16 17 18 19 20 21 12 13 14 15 16 17 18 10 11 12 13 14 15 16 22 23 24 25 26 27 28 19 20 21 22 23 24 25 17 18 19 20 21 22 23 29 30 31 26 27 28 29 30 24 25 26 27 28 29 30 31
Gambas
Click this link to run this code
Public Sub Main()
Shell "ls -aul"
End
Output:
total 36364 drwxr-xr-x 88 charlie charlie 4096 May 29 10:26 . drwxr-xr-x 5 root root 4096 May 26 15:44 .. drwxr-xr-x 2 charlie charlie 4096 May 29 10:54 15PuzzleGame drwx------ 3 charlie charlie 4096 May 28 13:51 .adobe drwxr-xr-x 4 charlie charlie 4096 May 28 13:52 .audacity-data drwxr-xr-x 4 charlie charlie 4096 May 28 13:51 .barcode etc....
Genie
[indent=4]
/*
Execute system command, in Genie
valac executeSystemCommand.gs
./executeSystemCommand
*/
init
try
// Non Blocking
Process.spawn_command_line_async("ls")
except e : SpawnError
stderr.printf("%s\n", e.message)
- Output:
Output is asynchronous (could be made synchronous with spawn_command_line_sync), and elided here for the sample capture.
prompt$ valac executeSystemCommand.gs prompt$ ./executeSystemCommand ... aplusb executeSystemCommand hello.gs helloNoNewline.gs memavail progress-bar readfile.vapi stringsample.vala ...
gnuplot
!ls
Go
package main
import (
"log"
"os"
"os/exec"
)
func main() {
cmd := exec.Command("ls", "-l")
cmd.Stdout = os.Stdout
cmd.Stderr = os.Stderr
if err := cmd.Run(); err != nil {
log.Fatal(err)
}
}
Groovy
println "ls -la".execute().text
GUISS
Start,Programs,Accessories,MSDOS Prompt,Type:dir[enter]
Haskell
import System.Cmd
main = system "ls"
See also: the System.Process module
HicEst
SYSTEM(CoMmand='pause')
SYSTEM(CoMmand='dir & pause')
HolyC
HolyC is the official programming language for The Temple Operating System (TempleOS). The Temple Operating System interpreter executes just-in-time compiled HolyC code. All HolyC code is effectively executed as system commands.
For example, to execute the Dir
command:
Dir;
Icon and Unicon
The code below selects the 'ls' or 'dir' command at runtime based on the UNIX feature.
Unicon extends system to allow specification of files and a wait/nowait parameter as in the examples below.
IDL
$ls
Will execute "ls" with output to the screen.
spawn,"ls",result
will execute it and store the result in the string array "result".
spawn,"ls",unit=unit
will execute it asynchronously and direct any output from it into the LUN "unit" from whence it can be read at any (later) time.
Io
System runCommand("ls") stdout println
IS-BASIC
100 EXT "dir"
J
The system command interface in J is provided by the standard "task" script:
load'task'
NB. Execute a command and wait for it to complete
shell 'dir'
NB. Execute a command but don't wait for it to complete
fork 'notepad'
NB. Execute a command and capture its stdout
stdout =: shell 'dir'
NB. Execute a command, provide it with stdin,
NB. and capture its stdout
stdin =: 'blahblahblah'
stdout =: stdin spawn 'grep blah'
Note that on unix systems, you can also use the 2!:x family of foreign verbs to execute system commands.
Java
import java.util.Scanner;
import java.io.*;
public class Program {
public static void main(String[] args) {
try {
Process p = Runtime.getRuntime().exec("cmd /C dir");//Windows command, use "ls -oa" for UNIX
Scanner sc = new Scanner(p.getInputStream());
while (sc.hasNext()) System.out.println(sc.nextLine());
}
catch (IOException e) {
System.out.println(e.getMessage());
}
}
}
There are two ways to run system commands. The simple way, which will hang the JVM (I would be interested in some kind of reason). -- this happens because the the inputStream buffer fills up and blocks until it gets read. Moving your .waitFor after reading the InputStream would fix your issue (as long as your error stream doesn't fill up)
import java.io.IOException;
import java.io.InputStream;
public class MainEntry {
public static void main(String[] args) {
executeCmd("ls -oa");
}
private static void executeCmd(String string) {
InputStream pipedOut = null;
try {
Process aProcess = Runtime.getRuntime().exec(string);
aProcess.waitFor();
pipedOut = aProcess.getInputStream();
byte buffer[] = new byte[2048];
int read = pipedOut.read(buffer);
// Replace following code with your intends processing tools
while(read >= 0) {
System.out.write(buffer, 0, read);
read = pipedOut.read(buffer);
}
} catch (IOException e) {
e.printStackTrace();
} catch (InterruptedException ie) {
ie.printStackTrace();
} finally {
if(pipedOut != null) {
try {
pipedOut.close();
} catch (IOException e) {
}
}
}
}
}
And the right way, which uses threading to read the InputStream given by the process.
import java.io.IOException;
import java.io.InputStream;
public class MainEntry {
public static void main(String[] args) {
// the command to execute
executeCmd("ls -oa");
}
private static void executeCmd(String string) {
InputStream pipedOut = null;
try {
Process aProcess = Runtime.getRuntime().exec(string);
// These two thread shall stop by themself when the process end
Thread pipeThread = new Thread(new StreamGobber(aProcess.getInputStream()));
Thread errorThread = new Thread(new StreamGobber(aProcess.getErrorStream()));
pipeThread.start();
errorThread.start();
aProcess.waitFor();
} catch (IOException e) {
e.printStackTrace();
} catch (InterruptedException ie) {
ie.printStackTrace();
}
}
}
//Replace the following thread with your intends reader
class StreamGobber implements Runnable {
private InputStream Pipe;
public StreamGobber(InputStream pipe) {
if(pipe == null) {
throw new NullPointerException("bad pipe");
}
Pipe = pipe;
}
public void run() {
try {
byte buffer[] = new byte[2048];
int read = Pipe.read(buffer);
while(read >= 0) {
System.out.write(buffer, 0, read);
read = Pipe.read(buffer);
}
} catch (IOException e) {
e.printStackTrace();
} finally {
if(Pipe != null) {
try {
Pipe.close();
} catch (IOException e) {
}
}
}
}
}
JavaScript
JavaScript does not have any facilities to interact with the OS. However, host environments can provide this ability.
var shell = new ActiveXObject("WScript.Shell");
shell.run("cmd /c dir & pause");
runCommand("cmd", "/c", "dir", "d:\\");
print("===");
var options = {
// can specify arguments here in the options object
args: ["/c", "dir", "d:\\"],
// capture stdout to the options.output property
output: ''
};
runCommand("cmd", options);
print(options.output);
Joy
<
"ls" system.
Julia
The Julia manual has an excellent section on this topic, which is worth a read. The short answer on Linux is:
run(`ls`)
- Output:
$ ls bitmap_bresenham_line.jl completed single_link_list_collection.jl color_quantization_in.png execute_system_command.jl single_link_list_insert.jl color_quantization.jl README.md support $ julia execute_system_command.jl bitmap_bresenham_line.jl completed single_link_list_collection.jl color_quantization_in.png execute_system_command.jl single_link_list_insert.jl color_quantization.jl README.md support
K
Execute "ls"
\ls
Execute "ls" and capture the output in the variable "r":
r: 4:"ls"
Kotlin
// version 1.0.6
import java.util.Scanner
fun main(args: Array<String>) {
val proc = Runtime.getRuntime().exec("cmd /C dir") // testing on Windows 10
Scanner(proc.inputStream).use {
while (it.hasNextLine()) println(it.nextLine())
}
}
Lang5
For one-word commands:
'ls system
For multi-word commands:
"ls -a" system
Lasso
local(
path = file_forceroot,
ls = sys_process('/bin/ls', (:'-l', #path)),
lswait = #ls -> wait
)
'<pre>'
#ls -> read
'</pre>'
total 16 drwxr-xr-x 8 _lasso staff 272 Nov 10 08:13 mydir -rw-r--r-- 1 _lasso staff 38 Oct 29 16:05 myfile.lasso -rw-r--r--@ 1 _lasso staff 175 Oct 29 18:18 rosetta.lasso
LFE
In the LFE REPL:
> (os:cmd "ls -alrt")
That will display output on a single line, with literal newlines.
For pretty output, compose with io:format
:
> (io:format (os:cmd "ls -alrt"))
Liberty BASIC
drive1$ = left$(Drives$,1)
run "cmd.exe /";drive1$;" dir & pause"
Limbo
There is no equivalent to Unix's exec() in Inferno per se; commands are just modules that have at least an init() function with the correct signature, and are loaded the same way as any other module. (As a result, there's nothing in the language or OS that prevents a program from acting as both a command and a library except convention.)
This version passes its argument list through to ls:
implement Runls;
include "sys.m"; sys: Sys;
include "draw.m";
include "sh.m";
Runls: module {
init: fn(ctxt: ref Draw->Context, args: list of string);
};
init(ctxt: ref Draw->Context, args: list of string)
{
sys = load Sys Sys->PATH;
ls := load Command "/dis/ls.dis";
if(ls == nil)
die("Couldn't load /dis/ls.dis");
ls->init(ctxt, "ls" :: tl args);
}
die(s: string)
{
sys->fprint(sys->fildes(2), "runls: %s: %r", s);
raise "fail:errors";
}
It's not strictly necessary to pass the graphics context to ls, but it is generally a good idea to do so when calling another program.
Lingo
sx = xtra("Shell").new()
if the platform contains "win" then
put sx.shell_cmd("dir")
else
put sx.shell_cmd("ls")
end if
Locomotive Basic
The Amstrad CPC464 uses a ROM based basic interpreter, so every statement within the program is a system command. If a command without a line number is typed, whilst the computer is in a ready state, the command gets executed immediately. There is no pause command, so in this example, we use the list command (which exhibits totally different behaviour to a pause command):
LIST
Logo
The lines of output of the SHELL command are returned as a list.
print first butfirst shell [ls -a] ; ..
Logtalk
Using the standard library:
os::shell('ls -a').
Lua
-- just executing the command
os.execute("ls")
-- to execute and capture the output, use io.popen
local f = io.popen("ls") -- store the output in a "file"
print( f:read("*a") ) -- print out the "file"'s content
M2000 Interpreter
Locale 1033 // for the chr$(string) : converτ ANSI to UTF16LE
Dos "chdir "+quote$(dir$)+"&& dir /w > out.txt";
Wait 100
Print "Press Space or Mouse to see next page"
A$=chr$(eval$(buffer("out.txt")))
Report a$ // view text using proportional typing, and at pages, with 3/4height scroll
M4
syscmd(ifdef(`__windows__',`dir',`ls'))
Make
make can use system command in either definition of variables or in the targets
in definition
contents=$(shell cat foo)
curdir=`pwd`
in target
mytarget:
cat foo | grep mytext
Maple
ssystem("dir");
Mathematica / Wolfram Language
Run["ls"]
MATLAB
To execute system commands in MATLAB, use the "system" keyword.
Sample Usage:
>> system('PAUSE')
Press any key to continue . . .
ans =
0
Maxima
system("dir > list.txt")$
MAXScript
dosCommand "pause"
Mercury
:- module execute_sys_cmd.
:- interface.
:- import_module io.
:- pred main(io::di, io::uo) is det.
:- implementation.
main(!IO) :-
io.call_system("ls", _Result, !IO).
min
!dir
Modula-2
MODULE tri;
FROM SYSTEM IMPORT ADR;
FROM SysLib IMPORT system;
IMPORT TextIO, InOut, ASCII;
VAR fd : TextIO.File;
ch : CHAR;
PROCEDURE SystemCommand (VAR command : ARRAY OF CHAR) : BOOLEAN;
BEGIN
IF system (ADR (command) ) = 0 THEN
RETURN TRUE
ELSE
RETURN FALSE
END
END SystemCommand;
BEGIN
IF SystemCommand ("ls -1 tri.mod | ") = TRUE THEN
InOut.WriteString ("No error reported.")
ELSE
InOut.WriteString ("Error reported!")
END;
LOOP
InOut.Read (ch);
InOut.Write (ch);
IF ch < ' ' THEN EXIT END
END;
InOut.WriteLn;
InOut.WriteBf
END tri.
Modula-3
This code requires the UNSAFE
keyword because M3toC
deals with C strings (which are pointers), and are implemented in Modula-3 as UNTRACED
, meaning they are not garbage collected, which is why the code calls FreeCopiedS()
.
Also note the EVAL
keyword, which ignores the return value of a function.
UNSAFE MODULE Exec EXPORTS Main;
IMPORT Unix, M3toC;
VAR command := M3toC.CopyTtoS("ls");
BEGIN
EVAL Unix.system(command);
M3toC.FreeCopiedS(command);
END Exec.
MUMPS
ANSI MUMPS doesn't allow access to the operating system except possibly through the View command and $View function, both of which are implementation specific. Intersystems' Caché does allow you to create processes with the $ZF function, and if the permissions for the Caché process allow it you can perform operating system commands.
In Caché on OpenVMS in an FILES-11 filesystem ODS-5 mode this could work:
Set X=$ZF(-1,"DIR")
In GT.M on OpenVMS, the following will work:
ZSY "DIR"
GT.M on UNIX is the same:
ZSY "ls"
Note: $ZF in GT.M is Unicode version of $F[ind].
Nanoquery
shell("ls")
NetRexx
/* NetRexx */
options replace format comments java crossref symbols binary
import java.util.Scanner
runSample(arg)
return
-- 10:43, 27 August 2022 (UTC)10:43, 27 August 2022 (UTC)10:43, 27 August 2022 (UTC)10:43, 27 August 2022 (UTC)10:43, 27 August 2022 (UTC)10:43, 27 August 2022 (UTC)10:43, 27 August 2022 (UTC)10:43, 27 August 2022 (UTC)10:43, 27 August 2022 (UTC)10:43, 27 August 2022 (UTC)10:43, 27 August 2022 (UTC)10:43, 27 August 2022 (UTC)10:43, 27 August 2022 (UTC)10:43, 27 August 2022 (UTC)10:43, 27 August 2022 (UTC)~~
method runSample(arg) private static
parse arg command
if command = '' then command = 'ls -oa' -- for Windows change to: 'cmd /C dir'
do
say 'Executing command:' command
jprocess = Runtime.getRunTime().exec(command)
jscanner = Scanner(jprocess.getInputStream())
loop label scanning while jscanner.hasNext()
say jscanner.nextLine()
end scanning
catch ex = IOException
ex.printStackTrace()
end
return
NewLISP
(exec "ls")
Nim
import osproc
let exitCode = execCmd "ls"
let (output, exitCode2) = execCmdEx "ls"
Objective-C
NSTask runs an external process with explicit path and arguments.
void runls()
{
[[NSTask launchedTaskWithLaunchPath:@"/bin/ls"
arguments:@[]] waitUntilExit];
}
If you need to run a system command, invoke the shell:
void runSystemCommand(NSString *cmd)
{
[[NSTask launchedTaskWithLaunchPath:@"/bin/sh"
arguments:@[@"-c", cmd]]
waitUntilExit];
}
Complete usage example:
#import <Foundation/Foundation.h>
void runSystemCommand(NSString *cmd)
{
[[NSTask launchedTaskWithLaunchPath:@"/bin/sh"
arguments:@[@"-c", cmd]]
waitUntilExit];
}
int main(int argc, const char **argv)
{
@autoreleasepool {
runSystemCommand(@"ls");
}
return 0;
}
Or use the C method above.
OCaml
Just run the command:
Sys.command "ls"
To capture the output of the command:
#load "unix.cma"
let syscall cmd =
let ic, oc = Unix.open_process cmd in
let buf = Buffer.create 16 in
(try
while true do
Buffer.add_channel buf ic 1
done
with End_of_file -> ());
let _ = Unix.close_process (ic, oc) in
(Buffer.contents buf)
let listing = syscall "ls" ;;
a more complete version which also returns the contents from stderr, and checks the exit-status, and where the environment can be specified:
let check_exit_status = function
| Unix.WEXITED 0 -> ()
| Unix.WEXITED r -> Printf.eprintf "warning: the process terminated with exit code (%d)\n%!" r
| Unix.WSIGNALED n -> Printf.eprintf "warning: the process was killed by a signal (number: %d)\n%!" n
| Unix.WSTOPPED n -> Printf.eprintf "warning: the process was stopped by a signal (number: %d)\n%!" n
;;
let syscall ?(env=[| |]) cmd =
let ic, oc, ec = Unix.open_process_full cmd env in
let buf1 = Buffer.create 96
and buf2 = Buffer.create 48 in
(try
while true do Buffer.add_channel buf1 ic 1 done
with End_of_file -> ());
(try
while true do Buffer.add_channel buf2 ec 1 done
with End_of_file -> ());
let exit_status = Unix.close_process_full (ic, oc, ec) in
check_exit_status exit_status;
(Buffer.contents buf1,
Buffer.contents buf2)
val syscall : ?env:string array -> string -> string * string
Octave
system("ls");
Oforth
System cmd("pause")
Oz
{OS.system "ls" _}
A more sophisticated example can be found here.
PARI/GP
system("ls")
Pascal
Program ExecuteSystemCommand;
uses
SysUtils;
begin
ExecuteProcess('/bin/ls', '-alh');
end.
PascalABC.NET
##
exec('cmd.exe','/c dir /p');
PDP-11 Assembly
PDP-11 running Unix
; Execute a file - the equivalent of system() in stdio
;
; On entry, r1=>nul-terminated command string
; On exit, VS=Couldn't fork
; VC=Forked successfully, r0=return value
;
.CLIsystem
trap 2 ; fork()
br CLIchild ; Child process returns here
bcc CLIparent ; Parent process returns here
mov (sp)+,r1
tst (sp)+
sev ; Couldn't fork, set V
rts pc
.CLIparent
mov r0,-(sp) ; Save child's PID
.CLIwait
trap 7 ; wait()
cmp r0,(sp)
beq CLIfinished
cmp r0,#&FFFF
bne CLIwait ; Loop until child finished
.CLIfinished
tst (sp)+ ; Drop child's PID
mov r1,r0 ; R0=return value
mov (sp)+,r1 ; Restore R1
tst (sp)+ ; Drop original R0
swab r0 ; Move return value to bottom byte
rts pc
; CLI child process
; -----------------
.CLIchild
clr -(sp) ; end of string array
mov r1,-(sp) ; => command string
mov #UXsh3,-(sp) ; => "-c"
mov #UXsh2,-(sp) ; => "sh"
mov #&890B,TRAP_BUF ; exec
mov #UXsh1,TRAP_BUF+2 ; => "/bin/sh"
mov sp,TRAP_BUF+4 ; => pointers to command strings
;mov SV_ENVPTR,TRAP_BUF+6 ; => "PATH=etc"
trap 0 ; indir()
EQUW TRAP_BUF ; exec(shell, parameters)
add #8,sp ; If we get back, we didn't fork, we spawned
mov (sp)+,r1 ; So, restore registers
clr (sp)+ ; and return exit value in R0
rts pc
.UXsh1 EQUS "/bin/sh",0
.UXsh2 EQUS "sh",0
.UXsh3 EQUS "-c",0
ALIGN
.TRAP_BUF
EQUW 0
EQUW 0
EQUW 0
EQUW 0
So, call with, for example:
mov #cmd_ls,r1 ; => "ls" command string
jsr pc,CLIsystem
...
.cmd_ls EQUS "ls",0
Perl
my @results = qx(ls); # run command and return STDOUT as a string
my @results = `ls`; # same, alternative syntax
system "ls"; # run command and return exit status; STDOUT of command goes program STDOUT
print `ls`; # same, but with back quotes
exec "ls"; # replace current process with another
See also: http://perldoc.perl.org/perlipc.html#Using-open()-for-IPC http://perldoc.perl.org/IPC/Open3.html
Phix
without js string cmd = iff(platform()=WINDOWS?"dir":"ls") system(cmd) integer res = system_exec("pause",4)
system_exec allows you to specify whether you want a command shell or not, and whether to wait for a result. In the case of pause, the 4 signifies that we need a shell and we want to wait for it to complete.
PHP
The first line execute the command and the second line display the output:
@exec($command,$output);
echo nl2br($output);
Note:The '@' is here to prevent error messages to be displayed, 'nl2br' translate '\n' chars to 'br' in HTML.
Other:
$results = `ls`;
# runs command and returns its STDOUT as a string
system("ls");
# runs command and returns its exit status; its STDOUT gets output to our STDOUT
echo `ls`;
# the same, but with back quotes
passthru("ls");
# like system() but binary-safe
See also: proc_open()
PicoLisp
(call "ls")
Pike
int main(){
// Process.run was added in Pike 7.8 as a wrapper to simplify the use of Process.create_process()
mapping response = Process.run("ls -l");
// response is now a map containing 3 fields
// stderr, stdout, and exitcode. We want stdout.
write(response["stdout"] + "\n");
// with older versions of pike it's a bit more complicated:
Stdio.File stdout = Stdio.File();
Process.create_process(({"ls", "-l"}), ([ "stdout" : stdout->pipe() ]) );
write(stdout->read() + "\n");
}
Plain English
A command is a string.
A parameter is a string.
To run:
Start up.
Execute "dir" on the command line.
Shut down.
To execute a command on the command line:
Put "/c " then the command into a parameter.
Null terminate the parameter.
Put "cmd" into a string.
Null terminate the string.
Call "shell32.dll" "ShellExecuteA" with nil and nil and the string's first and the parameter's first and nil and 1.
Pop11
The sysobey function runs commands using a shell:
sysobey('ls');
PowerShell
Since PowerShell is a shell, running commands is the default operation.
dir
ls
Get-ChildItem
are all equivalent (the first two are aliases for the third) but they are PowerShell-native commands. If one really needs to execute dir
(which is no program but rather a built-in command in cmd.exe
) this can be achieved by
cmd /c dir
Prolog
shell('ls').
PureBasic
ImportC "msvcrt.lib"
system(str.p-ascii)
EndImport
If OpenConsole()
system("dir & pause")
Print(#CRLF$ + #CRLF$ + "Press ENTER to exit")
Input()
CloseConsole()
EndIf
Python
import os
exit_code = os.system('ls') # Just execute the command, return a success/fail code
output = os.popen('ls').read() # If you want to get the output data. Deprecated.
or
import subprocess
# if the exit code was non-zero these commands raise a CalledProcessError
exit_code = subprocess.check_call(['ls', '-l']) # Python 2.5+
assert exit_code == 0
output = subprocess.check_output(['ls', '-l']) # Python 2.7+
or
from subprocess import PIPE, Popen, STDOUT
p = Popen('ls', stdout=PIPE, stderr=STDOUT)
print p.communicate()[0]
Note: The latter is the preferred method for calling external processes, although cumbersome, it gives you finer control over the process.
or
import commands
stat, out = commands.getstatusoutput('ls')
if not stat:
print out
Quackery
$ \
import os
exit_code = os.system('ls')
\ python
- Output:
Quackery Quick Reference.pdf extensionsX.qky READ ME FIRST.txt quackery.py The Book of Quackery for print.pdf sundry The Book of Quackery.pdf turtleduck.qky bigrat.qky
R
system("ls")
output=system("ls",intern=TRUE)
Racket
#lang racket
;; simple execution of a shell command
(system "ls")
;; capture output
(string-split (with-output-to-string (λ() (system "ls"))) "\n")
;; Warning: passing random string to be run in a shell is a bad idea!
;; much safer: avoids shell parsing, arguments passed separately
(system* "/bin/ls" "-l")
;; avoid specifying the executable path
(system* (find-executable-path "/bin/ls") "-l")
Raku
(formerly Perl 6)
run "ls" orelse .die; # output to stdout
my @ls = qx/ls/; # output to variable
my $cmd = 'ls';
@ls = qqx/$cmd/; # same thing with interpolation
Raven
Back tick string is auto executed:
`ls -la` as listing
Or specifically on any string:
'ls -la' shell as listing
REBOL
; Capture output to string variable:
x: "" call/output "dir" x
print x
; The 'console' refinement displays the command output on the REBOL command line.
call/console "dir *.r"
call/console "ls *.r"
call/console "pause"
; The 'shell' refinement may be necessary to launch some programs.
call/shell "notepad.exe"
Red
call/show %pause ;The /show refinement forces the display of system's shell window (Windows only).
call/show %dir
call/show %notepad.exe
REXX
Since REXX is a shell scripting language, it's easy to execute commands:
"dir /a:d"
Ring
system("dir")
Ruby
string = `ls`
# runs command and returns its STDOUT as a string
string = %x{ls}
# ditto, alternative syntax
system "ls"
# runs command and returns its exit status; its STDOUT gets output to our STDOUT
print `ls`
#The same, but with back quotes
exec "ls"
# replace current process with another
# call system command and read output asynchronously
io = IO.popen('ls')
# ... later
io.each {|line| puts line}
Run BASIC
print shell$("ls") ' prints the returned data from the OS
a$ = shell$("ls") ' holds returned data in a$
Rust
use std::process::Command;
fn main() {
let output = Command::new("ls").output().unwrap_or_else(|e| {
panic!("failed to execute process: {}", e)
});
println!("{}", String::from_utf8_lossy(&output.stdout));
}
Scala
import scala.sys.process.Process
Process("ls", Seq("-oa"))!
Scheme
(system "ls")
Seed7
System commands can make a program unportable. Unix, Linux and BSD use the command ls, while Windows respectively DOS use the command dir. The format written by ls respectively dir depends on operating system and locale. The library osfiles.s7i defines the function readDir, which reads the contents of a directory in a portable way. ReadDir works independend from operating system and locale and supports also Unicode filenames. Anyway, the task was to use a system command, so here is the example:
$ include "seed7_05.s7i";
include "shell.s7i";
const proc: main is func
begin
shellCmd("ls");
end func;
SETL
system("ls");
Sidef
# Pipe in read-only mode
%p(ls).open_r.each { |line|
print line;
};
var str1 = `ls`; # backtick: returns a string
var str2 = %x(ls); # ditto, alternative syntax
Sys.system('ls'); # system: executes a command and prints the result
Sys.exec('ls'); # replaces current process with another
Slate
Run a command normally through the shell:
Platform run: 'ls'.
Run a command (this way takes advantage of the 'does not understand' message for the shell object and calls the Platform run: command above with a specific command):
shell ls: '*.slate'.
Smalltalk
Smalltalk system: 'ls'.
SQL PL
In Linux or UNIX:
!ls
Output:
db2 => !ls adm ctrlhamirror fm.ip-10-0-0-85.reg lib64 profile.env security64 adsm dasfcn function log python32 spmlog backup db2cshrc gskit map python64 sqldbdir bin db2dump hmonCache misc rdf tmp bnd db2nodes.cfg include msg Readme tools cfg db2profile infopop nodes ruby32 uif cfgcache db2systm java nodes.reg ruby64 usercshrc conv doc json pd samples userprofile ctrl fm.db2-1.reg lib php32 security ctrlha fm.db2-model.reg lib32 php64 security32
In Windows:
!dir
Standard ML
Just run the command:
OS.Process.system "ls"
Stata
Stata has a built-in dir command. However, it's also possible to run arbitrary external programs using the shell or winexec commands.
The command ! (or equivalently shell), opens a Windows console to run the command, while winexec does not.
!dir
* print a message and wait
!echo Ars Longa Vita Brevis & pause
* load Excel from Stata
!start excel
* run a Python program (Python must be installed and accessible in the PATH environment variable)
!python preprocessing.py
* load Windows Notepad
winexec notepad
Tcl
puts [exec ls]
This page uses "ls" as the primary example. For what it's worth, Tcl has built-in primitives for retrieving lists of files so one would rarely ever directly exec an ls command.
It is also possible to execute a system command by "open"ing it through a pipe from whence any output of the command can be read at any (later) time. For example:
set io [open "|ls" r]
would execute "ls" and pipe the result into the channel whose name is put in the "io" variable. From there one could receive it either line by line like this:
set nextline [gets $io]
or read the whole shebang in a fell swoop:
set lsoutput [read $io]
If the command is opened "rw", it is even possible to send it user input through the same handle, though care must be taken with buffering in that case.
exec C:/Windows/System32/taskmgr.exe &
Runs the Task Manager on Windows. If running from a Tcl/Tk Gui the [ & ] prevents blocking the Gui.
Toka
needs shell
" ls" system
TUSCRIPT
$$ MODE TUSCRIPT
system=SYSTEM ()
IF (system=="WIN") THEN
EXECUTE "dir"
ELSEIF (system.sw."LIN") THEN
EXECUTE "ls -l"
ENDIF
UNIX Shell
UNIX shells are designed to run system commands as a default operation.
ls
If one wishes to replace the shell process with some other command (chain into some command with no return) one can use the exec shell built-in command.
exec ls
Command substitution
One can also capture the command's standard output in a variable.
With Bourne Shell:
output=`ls`
With Korn Shell or any modern shell:
output=$(ls)
- Note 1: in
`ls`
, these are "backticks" rather than quotes or apostrophes. - Note 2: the $(...) form works in all modern shells, including the Almquist Shell, Bash and any POSIX shell.
- The old `backticks` can also be used in the newer shells, but their users prefer the $(...) form when discussing such things in e-mail, on USENET, or in other online forums (such as this wiki). The only reason to use `backticks` is in scripts for old Bourne Shell.
The `...` form is difficult to nest, but the $(...) form is very nestable.
output=`expr \`echo hi | wc -c\` - 1`
output=$(expr $(echo hi | wc -c) - 1)
Both forms, `backticks` and $(...), also work inside double-quoted strings. This prevents file name expansion and also prevents word splitting.
echo "Found: `grep 80/tcp /etc/services`"
echo "Found: $(grep 80/tcp /etc/services)"
C Shell
C Shell also runs system commands, and has an exec built-in command, exactly like Bourne Shell.
ls # run command, return to shell
exec ls # replace shell with command
`Backticks` are slightly different. When inside double quotes, as "`...`", C Shell splits words at newlines, like "line 1" "line 2" ..., but preserves spaces and tabs.
set output=( "`grep 80/ /etc/services`" )
echo "Line 1: $output[1]"
echo "Line 2: $output[2]"
Ursa
decl string<> arg
decl string<> output
decl iodevice iod
append "ls" arg
set iod (ursa.util.process.start arg)
set output (iod.readlines)
for (decl int i) (< i (size output)) (inc i)
out output<i> endl console
end for
Ursala
The library function, ask, parameterized by a shell descriptor, such as bash, spawns a process that interacts with that shell by feeding it a list of commands, and returns a transcript of the interaction.
Note that the output from the spawned process is captured and returned only, not sent to the standard output stream of the parent.
Here is a self-contained command line application providing a limited replacement for the ls command.
#import std
#import cli
#executable ('parameterized','')
myls = <.file$[contents: --<''>]>@hm+ (ask bash)/0+ -[ls --color=no]-!
The color option is needed to suppress terminal escape sequences.
VBScript
Set objShell = CreateObject("WScript.Shell")
objShell.Run "%comspec% /K dir",3,True
Vedit macro language
system("dir", DOS)
The above does not work on 64-bit Windows versions which do not have 16-bit DOS emulation. In this case, you need to call cmd.exe explicitly:
system('cmd /k "dir"')
Visual Basic
Shelling out a sub task in Visual Basic is rather a pain if you need to wait for the task to complete, which is probably the usual case. But it is possible.
Attribute VB_Name = "mdlShellAndWait"
Option Explicit
Private Declare Function OpenProcess Lib "kernel32" _
(ByVal dwDesiredAccess As Long, ByVal bInheritHandle As Long, _
ByVal dwProcessId As Long) As Long
Private Declare Function GetExitCodeProcess Lib "kernel32" _
(ByVal hProcess As Long, lpExitCode As Long) As Long
Private Const STATUS_PENDING = &H103&
Private Const PROCESS_QUERY_INFORMATION = &H400
'
' Little function go get exit code given processId
'
Function ProcessIsRunning( processId as Long ) as Boolean
Dim exitCode as Long
Call GetExitCodeProcess(lProcessId, exitCode)
ProcessIsRunning = (exitCode = STATUS_PENDING)
End Function
' Spawn subprocess and wait for it to complete.
' I believe that the command in the command line must be an exe or a bat file.
' Maybe, however, it can reference any file the system knows how to "Open"
'
' commandLine is an executable.
' expectedDuration - is for poping up a dialog for whatever
' infoText - text for progressDialog dialog
Public Function ShellAndWait( commandLine As String, _
expectedDuration As Integer ) As Boolean
Dim inst As Long
Dim startTime As Long
Dim expirationTime As Long
Dim pid As Long
Dim expiresSameDay As Boolean
On Error GoTo HandleError
'Deal with timeout being reset at Midnight ($hitForBrains VB folks)
startTime = CLng(Timer)
expirationTime = startTime + expectedDuration
expiresSameDay = expirationTime < 86400
If Not expiresSameDay Then
expirationTime = expirationTime - 86400
End If
inst = Shell(commandLine, vbMinimizedNoFocus)
If inst <> 0 Then
pid = OpenProcess(PROCESS_QUERY_INFORMATION, False, inst)
Do While ProcessIsRunning( pid)
DoEvents
If Timer > expirationTime And (expiresSameDay Or Timer < startTime) Then
Exit Do
End If
Loop
ShellAndWait = True
Else
MsgBox ("Couldn't execute command: " & commandLine)
ShellAndWait = False
End If
Exit Function
HandleError:
MsgBox ("Couldn't execute command: " & commandLine)
ShellAndWait = False
End Function
Sub SpawnDir()
ShellAndWait("dir", 10)
End Sub
Visual Basic .NET
Module System_Command
Sub Main()
Dim cmd As New Process
cmd.StartInfo.FileName = "cmd.exe"
cmd.StartInfo.RedirectStandardInput = True
cmd.StartInfo.RedirectStandardOutput = True
cmd.StartInfo.CreateNoWindow = True
cmd.StartInfo.UseShellExecute = False
cmd.Start()
cmd.StandardInput.WriteLine("dir")
cmd.StandardInput.Flush()
cmd.StandardInput.Close()
Console.WriteLine(cmd.StandardOutput.ReadToEnd)
End Sub
End Module
V (Vlang)
import os
fn main() {
result := os.execute('cmd /c dir')
if result.output !='' {println(result.output)}
else {println('Error: not working') exit(1)}
}
Wart
system "ls"
Wren
Wren CLI doesn't currently expose a way to execute a system command.
However, if Wren is embedded in (say) a suitable Go program, then we can ask the latter to do it for us.
/* Execute_a_system_command.wren */
class Command {
foreign static exec(name, param) // the code for this is provided by Go
}
Command.exec("ls", "-lt")
System.print()
Command.exec("dir", "")
which we embed in the following Go program and run it.
/* Execute_a_system_command.go*/
package main
import (
wren "github.com/crazyinfin8/WrenGo"
"log"
"os"
"os/exec"
)
type any = interface{}
func execCommand(vm *wren.VM, parameters []any) (any, error) {
name := parameters[1].(string)
param := parameters[2].(string)
var cmd *exec.Cmd
if param != "" {
cmd = exec.Command(name, param)
} else {
cmd = exec.Command(name)
}
cmd.Stdout = os.Stdout
cmd.Stderr = os.Stderr
if err := cmd.Run(); err != nil {
log.Fatal(err)
}
return nil, nil
}
func main() {
vm := wren.NewVM()
fileName := "Execute_a_system_command.wren"
methodMap := wren.MethodMap{"static exec(_,_)": execCommand}
classMap := wren.ClassMap{"Command": wren.NewClass(nil, nil, methodMap)}
module := wren.NewModule(classMap)
vm.SetModule(fileName, module)
vm.InterpretFile(fileName)
vm.Free()
}
x86 Assembly
32 bit
; Executes '/bin/ls'
; Build with:
; nasm -felf32 execls.asm
; ld -m elf_i386 execls.o -o execls
global _start
section .text
_start:
mov eax, 0x0B ; sys_execve(char *str, char **args, char **envp)
mov ebx, .path ; pathname
push DWORD 0
push DWORD .path
lea ecx, [esp] ; arguments [pathname]
xor edx, edx ; environment variables []
int 0x80 ; syscall
.path:
db '/bin/ls', 0x00
Yabasic
system("dir")
//It will return the exit code of the command; its output (if any) will be lost.
print system$("dir")
//Returns the output as a large string.
zkl
System.cmd(System.isWindows and "dir" or "ls")
ZX Spectrum Basic
The ZX Spectrum uses a ROM based basic interpreter, so every statement within the program is a system command. If a command without a line number is typed, whilst the computer is in a ready state, the command gets executed immediately:
PAUSE 100
- Programming Tasks
- Programming environment operations
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- Pages with too many expensive parser function calls