如何使用多个命令运行NSTask

Question

我正在尝试使NSTask运行这样的命令:

ps -clx | grep'Finder'| awk'{print $ 2}'

这是我的方法

- (void) processByName:(NSString*)name {
    NSTask *task1 = [[NSTask alloc] init];
    NSPipe *pipe1 = [NSPipe pipe];
    [task1 waitUntilExit];
    [task1 setLaunchPath: @"/bin/ps"];
    [task1 setArguments: [NSArray arrayWithObjects: @"-clx", nil]];
    [task1 setStandardOutput: pipe1];

    NSTask *task2 = [[NSTask alloc] init];
    NSPipe *pipe2 = [NSPipe pipe];
    [task2 setLaunchPath: @"/usr/bin/grep"];
    [task2 setArguments: [NSArray arrayWithObjects: @"'Finder'", nil]];
    [task2 setStandardInput:pipe1];
    [task2 setStandardOutput: pipe2];

    NSTask *task3 = [[NSTask alloc] init];
    NSPipe *pipe3 = [NSPipe pipe];
    [task3 setLaunchPath: @"/usr/bin/grep"];
    [task3 setArguments: [NSArray arrayWithObjects: @"'{print $2}'", nil]];
    [task3 setStandardInput:pipe2];
    [task3 setStandardOutput: pipe3];

    NSFileHandle *file = [pipe3 fileHandleForReading];

    [task1 launch];
    [task2 launch];
    [task3 launch];

    NSData *data;
    data = [file readDataToEndOfFile];

    NSString *string;
    string = [[NSString alloc] initWithData: data encoding: NSUTF8StringEncoding];

    NSLog(@"Result: %@", string);
}

但结果是公正的

结果:

我究竟做错了什么？

编辑

- (void) processByName:(NSString*)name {
    NSTask *task1 = [[NSTask alloc] init];
    NSPipe *pipe1 = [NSPipe pipe];
    [task1 waitUntilExit];
    [task1 setLaunchPath: @"/bin/ps"];
    [task1 setArguments: [NSArray arrayWithObjects: @"-clx", nil]];
    [task1 setStandardOutput: pipe1];

    NSTask *task2 = [[NSTask alloc] init];
    NSPipe *pipe2 = [NSPipe pipe];
    [task2 setLaunchPath: @"/usr/bin/grep"];
    [task2 setArguments: [NSArray arrayWithObjects: @"'Finder'", nil]];
    [task2 setStandardInput:pipe1];
    [task2 setStandardOutput: pipe2];

    NSTask *task3 = [[NSTask alloc] init];
    NSPipe *pipe3 = [NSPipe pipe];
    [task3 setLaunchPath: @"/usr/bin/grep"];
    [task3 setArguments: [NSArray arrayWithObjects: @"'{print $2}'", nil]];
    [task3 setStandardInput:pipe2];
    [task3 setStandardOutput: pipe3];

    NSFileHandle *file = [pipe3 fileHandleForReading];

    [task1 launch];
    [task2 launch];
    [task3 launch];

    [[NSNotificationCenter defaultCenter] addObserverForName:NSTaskDidTerminateNotification
                                                      object:task3
                                                       queue:nil
                                                  usingBlock:^(NSNotification* notification){

                                                      NSData * data = [file readDataToEndOfFile];

                                                      NSString * string;
                                                      string = [[NSString alloc] initWithData: data encoding: NSUTF8StringEncoding];
                                                      NSLog(@"Result: %@", string);
                                                  }];
}

Answer 1

任务在与代码分开的进程中运行,即异步运行.当你到达readDataToEndOfFile后两行时,它们可能还没有完成(它们可能还没有发射!).

如果你已经在这里的后台线程,你可以轮询他们的状态:while( ![task isRunning]){,或者如果你在主线程上,我建议使用GCD将其放入队列并在那里进行轮询.

实际上,比使用通知更好:

[task3 launch];

[[NSNotificationCenter defaultCenter] addObserverForName:NSTaskDidTerminateNotification
                                                  object:task3
                                                   queue:nil
                                              usingBlock:^{

    NSData * data = [file readDataToEndOfFile];

    NSString * string;
    string = [[NSString alloc] initWithData: data encoding: NSUTF8StringEncoding];

    NSLog(@"Result: %@", string);
}];

请参阅TN2050:在不轮询的情况下观察过程生命周期.每个NSTask都会NSTaskDidTerminateNotification在它终止时发送(理想情况下,你应该检查它的返回代码,而不是假设它成功运行).您可以在task3发送通知时创建要运行的块.