使用响应从可可（obj.c）执行shell脚本

Question

I have something like:

- (NSString *)unixSinglePathCommandWithReturn:(NSString *)command
{
NSPipe *newPipe = [NSPipe pipe];
NSFileHandle *readHandle = [newPipe fileHandleForReading];

NSTask *unixTask = [[NSTask alloc] init];
[unixTask setStandardOutput:newPipe];
[unixTask setLaunchPath:@"/bin/sh"];
[unixTask setArguments:[NSArray arrayWithObjects:@"-c", command , nil]]; 
[unixTask launch];
[unixTask waitUntilExit];

NSString *output = [[NSString alloc] initWithData:[readHandle readDataToEndOfFile] encoding:NSUTF8StringEncoding];

return output;
}

But it doesn't work as expected. I call it when i click a button. If i remove the line with 'waitUntilExit' it works as expected, but only once. When it's there, it doesn't work. I tried also some basic commands like 'ls' 'ping -c1 google.com' and stuff like that, but i can't get it to work somehow. If you have some different approach to run shell scripts in cocoa with receiving the response, please let me now. Thank you all :)

Answer 1

Hey, Kukosk. There's a comment on CocoaDev about NSLog() issues when running an NSTask. The fix is to set a pipe for stdin before launching the task:

[task setStandardInput:[NSPipe pipe]];

If you're relying on NSLog() only to check whether the task has run, this might fix your problem. Alternatively, you could try to present output in your GUI instead of using NSLog() .

Answer 2

The problem is that you aren't emptying the output buffers of the task. You can't simply launch a task and waitUntilDone unless the task also emits an extremely small amount of data.

waitUntilDone will obviously not work at all with a task that never exits.

For a task that emits any quantity of output, you need to set it up such that the output is read as it is generated. Typically, you use readInBackgroundAndNotify or a variant therein.

In any case, the top of the class description for NSTask has both links to the conceptual guide and to a series of examples that cover this.

Answer 3

Ah, there's a very important line in the docs you seem to have missed, one of those irritations that NextStep seems to like: "An NSTask object can only be run once. Subsequent attempts to run the task raise an error."

So, bag the wait, and add [unixTask release] before the return. When you want to run it again, remake the task.

NSTimer is like this.

Answer 4

For different approaches to run shell scripts in Cocoa have a look at AMShellWrapper, PseudoTTY.app or OpenFileKiller!

http://www.cocoadev.com/index.pl?NSTask