How to use NSTask run terminal commands in loop in consistent environment?(如何在一致的环境中循环使用 NSTask 运行终端命令?)

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问题描述

我想使用 NSTask 来模拟终端运行命令.代码如下.它可以循环获取输入并返回过程输出.

I want to use NSTask to simulate the Terminal to run commands. The codes as follows. It can get input in loop and return the process output.

int main(int argc, const char * argv[])
{
  @autoreleasepool {      
    while (1) {
        char str[80] = {0};
        scanf("%s", str);
        NSString *cmdstr = [NSString stringWithUTF8String:str];

        NSTask *task = [NSTask new];
        [task setLaunchPath:@"/bin/sh"];
        [task setArguments:[NSArray arrayWithObjects:@"-c", cmdstr, nil]];

        NSPipe *pipe = [NSPipe pipe];
        [task setStandardOutput:pipe];

        [task launch];

        NSData *data = [[pipe fileHandleForReading] readDataToEndOfFile];

        [task waitUntilExit];

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

    }
}

我的问题是:当一个循环结束时，运行环境恢复到初始化状态.比如默认运行路径是/Users/apple，我运行cd/把路径改成/，然后运行pwd，它返回 /Users/apple 而不是 /.

My question is: when a loop is end, the running environment restore to the initialization state. For example, the default running path is /Users/apple, and I run cd / to change the path to /, and then run pwd, it return the /Users/apple rather than the /.

那么如何使用 NSTask 来完全模拟终端呢?

So how can I use NSTask to simulate the Terminal completely ?

推荐答案

cd 和 pwd 是 shell 内置命令.如果你执行任务

cd and pwd are shell built-in commands. If you execute the task

/bin/sh -c "cd /"

无法将更改后的工作目录返回给调用进程.如果要设置变量MYVAR=myvalue，也会存在同样的问题.

there is no way of getting the changed working directory back to the calling process. The same problem exists if you want to set variables MYVAR=myvalue.

您可以尝试分别解析这些行并更新环境.但是像

You could try to parse these lines separately and update the environment. But what about multi-line commands like

for file in *.txt
do
    echo $file
done

您无法通过将每一行发送到单独的 NSTask 进程来模拟这一点.

You cannot emulate that by sending each line to separate NSTask processes.

你唯一能做的就是用 NSTask 启动一个single /bin/sh 进程，并将所有输入行提供给该过程的标准输入.但是你不能使用 readDataToEndOfFile 来读取输出，而必须异步读取(使用 [[pipe fileHandleForReading] waitForDataInBackgroundAndNotify]).

The only thing you could do is to start a single /bin/sh process with NSTask, and feed all the input lines to the standard input of that process. But then you can not use readDataToEndOfFile to read the output, but you have to read asynchronously (using [[pipe fileHandleForReading] waitForDataInBackgroundAndNotify]).

简而言之:您只能通过运行(单个)shell 来模拟终端.

So in short: you can simulate the Terminal only by running a (single) shell.

添加:也许您可以使用以下内容作为您的应用程序的起点.(我省略了所有的错误检查.)

ADDED: Perhaps you can use the following as a starting point for your app. (I have omitted all error checking.)

int main(int argc, const char * argv[])
{
    @autoreleasepool {

        // Commands are read from standard input:
        NSFileHandle *input = [NSFileHandle fileHandleWithStandardInput];

        NSPipe *inPipe = [NSPipe new]; // pipe for shell input
        NSPipe *outPipe = [NSPipe new]; // pipe for shell output

        NSTask *task = [NSTask new];
        [task setLaunchPath:@"/bin/sh"];
        [task setStandardInput:inPipe];
        [task setStandardOutput:outPipe];
        [task launch];

        // Wait for standard input ...
        [input waitForDataInBackgroundAndNotify];
        // ... and wait for shell output.
        [[outPipe fileHandleForReading] waitForDataInBackgroundAndNotify];

        // Wait asynchronously for standard input.
        // The block is executed as soon as some data is available on standard input.
        [[NSNotificationCenter defaultCenter] addObserverForName:NSFileHandleDataAvailableNotification
                                                          object:input queue:nil
                                                      usingBlock:^(NSNotification *note)
         {
             NSData *inData = [input availableData];
             if ([inData length] == 0) {
                 // EOF on standard input.
                 [[inPipe fileHandleForWriting] closeFile];
             } else {
                 // Read from standard input and write to shell input pipe.
                 [[inPipe fileHandleForWriting] writeData:inData];

                 // Continue waiting for standard input.
                 [input waitForDataInBackgroundAndNotify];
             }
         }];

        // Wait asynchronously for shell output.
        // The block is executed as soon as some data is available on the shell output pipe. 
        [[NSNotificationCenter defaultCenter] addObserverForName:NSFileHandleDataAvailableNotification
                                                          object:[outPipe fileHandleForReading] queue:nil
                                                      usingBlock:^(NSNotification *note)
         {
             // Read from shell output
             NSData *outData = [[outPipe fileHandleForReading] availableData];
             NSString *outStr = [[NSString alloc] initWithData:outData encoding:NSUTF8StringEncoding];
             NSLog(@"output: %@", outStr);

             // Continue waiting for shell output.
             [[outPipe fileHandleForReading] waitForDataInBackgroundAndNotify];
         }];

        [task waitUntilExit];

    }
    return 0;
}

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