Execute a system command: Difference between revisions
Line 110: | Line 110: | ||
set lsoutput [read $io] |
set lsoutput [read $io] |
||
If the command is opened "rw", it is even possible to send it user input through the same handle. |
|||
==[[UNIX Shell]]== |
==[[UNIX Shell]]== |
Revision as of 05:27, 3 February 2007
You are encouraged to solve this task according to the task description, using any language you may know.
In this task, the goal is to run either the ls
system command, or the pause
system command.
AppleScript
do shell script "ls" without altering line endings
C
Compiler: GCC 4.0.1
Platform: BSD
#include <stdlib.h> int main() { system("ls"); }
C++
Compiler: Visual C++ 2005
system("pause");
Haskell
Interpreter: GHCi 6.6
import System.Cmd main = system "ls"
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.
Objective-C
Compiler: GCC 4.0.1 (apple)
NSTask runs an external process with explicit path and arguments.
void runls() { [[NSTask launchedTaskWithLaunchPath:@"/bin/ls" arguments:[NSArray array]] waitUntilExit]; }
If you need to run a system command, invoke the shell:
void runSystemCommand(NSString *cmd) { [[NSTask launchedTaskWithLaunchPath:@"/bin/sh" arguments:[NSArray arrayWithObjects:@"-c", cmd, nil]] waitUntilExit]; }
Or use the C method above.
Perl
Interpreter: Perl
Note the use of grave quotes (or back ticks) instead of "normal" single quotes.
my $results = `ls`;
Back ticks as above returns the results, system as below does not.
system "ls";
Python
Interpreter: Python 2.5
import os 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
or
Interpreter:Python 2.4 (and above)
import subprocess output = subprocess.Popen('ls', shell=True, stdout=subprocess.PIPE).stdout print output.read()
Note: The latter is the preferred method for calling external processes, although cumbersome, it gives you finer control over the process.
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 unit "io". 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 $io]
If the command is opened "rw", it is even possible to send it user input through the same handle.
UNIX Shell
UNIX shells are designed to run system commands as a default operation.
ls
If one wants to capture the command's standard output:
CAPTUREDOUTPUT=$(ls)