壳牌程序管道C [英] Shell program pipes C

问题描述

我正在尝试运行一个小的Shell程序，确保我的代码正常运行的第一步是确保获得正确的命令和参数:

I am trying to run a small shell program and the first step to make sure my code is running properly is to make sure I get the correct command and parameters:

//Split the command and store each string in parameter[]
    cp = (strtok(command, hash));                      //Get the initial string (the command)
    parameter[0] = (char*) malloc(strlen(cp)+ 1);                     //Allocate some space to the first element in the array
    strncpy(parameter[0], cp, strlen(cp)+ 1);
    for(i = 1; i < MAX_ARG; i++)
    {
    cp = strtok(NULL, hash);                 //Check for each string in the array
    parameter[i] = (char*) malloc(strlen(cp)+ 1);
    strncpy(parameter[i], cp, strlen(cp)+ 1);                      //Store the result string in an indexed off array
        if(parameter[i]  == NULL)
        {
            break;
        }
    if(strcmp(parameter[i], "|") == 0)
    {
        cp = strtok(NULL, hash);
        parameter2[0] = (char*) malloc(strlen(cp)+ 1);
        strncpy(parameter2[0], cp, strlen(cp)+ 1);
        //Find the second set of commands and parameters
        for (j = 1; j < MAX_ARG; j++)
        {
            cp = strtok(NULL, hash);
            if (strlen(cp) == NULL)
            {
                break;
            }
            parameter2[j] = (char*) malloc(strlen(cp)+ 1);
            strncpy(parameter2[j], cp, strlen(cp)+ 1);
        }
        break;
    }

比较cp和NULL时出现问题，程序崩溃.我想要的是在第二个集合或参数的输入完成后退出循环(这是我尝试使用if(strlen(cp)== NULL)进行的操作

I am having a problem when I compare cp and NULL, my program crashes. What I want is to exit the loop once the entries for the second set or parameters have finished (which is what I tried doing with the if(strlen(cp) == NULL)

推荐答案

我可能误解了这个问题，但是您的程序永远不会参见管道字符|.

I may have misunderstood the question, but your program won't ever see the pipe character, |.

shell处理整个命令行，可以这么说，您的程序只会获得其在命令行中的份额.

The shell processes the entire command line, and your program will only be given it's share of the command line, so to speak.

示例:

cat file1 file2 | sed s/frog/bat/

在上面的示例中，仅使用两个参数file1和file2调用cat.另外，sed仅用一个参数调用:s/frog/bat/.

In the above example, cat is invoked with only two arguments, file1, and file2. Also, sed is invoked with only a single argument: s/frog/bat/.

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