如何使用多個命令運行NSTask

Question

我試圖做一個NSTask運行如下命令：

PS -clx | grep'Finder'| AWK '{打印$ 2}'

這裏是我的方法

- (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); 
} 

但結果只是

結果：

我在做什麼錯？

編輯

- (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

在一個單獨的進程從您的代碼運行，即異步地任務。他們可能還沒有完成（他們甚至可能還沒有發起！）在你到達readDataToEndOfFile後兩行。

如果你已經在這裏的後臺線程，你可以輪詢他們的狀態：while(![task isRunning]){，或者如果你在主線程，我建議使用GCD把它放到一個隊列，並在那裏進行輪詢。

事實上，比這更好的辦法是使用通知：

[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); 
}]; 

見TN2050: Observing Process Lifetime Without Polling。每個NSTask在終止時都會發送NSTaskDidTerminateNotification（理想情況下，您應該檢查其返回代碼，而不是假設它已成功運行）。當task3發送該通知時，您可以創建一個要運行的塊。

Answer 2

以下代碼適用於我。

NSTask *task1 = [[NSTask alloc] init]; 
NSPipe *pipe1 = [NSPipe pipe]; 
[task1 waitUntilExit]; 
[task1 setLaunchPath: @"/bin/sh"]; 
[task1 setArguments: [NSArray arrayWithObjects: @"-c",@"ps -A |grep -m1 Finder | awk '{print $1}'", nil]]; 
[task1 setStandardOutput: pipe1]; 
[task1 launch]; 

NSFileHandle *file = [pipe1 fileHandleForReading]; 
NSData * data = [file readDataToEndOfFile]; 

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