c - Execvp 与 "ls -l | wc"一起工作，但因“ls -l|wc”而失败

Question

我正在编写一个 shell，目前正在执行管道进程。我能够运行 "ls -l | wc"，但是当运行 "ls -l|wc" 时，进程失败。

我曾尝试使用 gdb 进行调试，但无法对其进行任何调试，因为它们看起来都等于相同的值(在解析后)。

运行 ls -l | 时wc 并在 parseCmdWithPipe 函数上设置断点并打印出我得到的局部变量:

argOne = {0x7fffffffdad0 "ls", 0x7fffffffdad3 "-l", 0x0}
argTwo = {0x7fffffffdad8 "wc", 0x0}   

当运行 ls -l|wc 并在 parseCmdWithPipe 函数上设置断点并打印出局部变量时，我得到:

argOne = {0x7fffffffd9b0 "ls", 0x7fffffffd9b3 "-l", 0x0}
argTwo = {0x7fffffffd9b8 "wc", 0x0}  

我用来解析和使用execvp的代码(第二个函数)

/* parse user input from fget */
int parseLine(char *line, char **argv) {
    line[strlen(line) - 1] = '\0';
    //This section tries to figure out if we have the case
    //"ls -l|wc", if it does it makes a new string of "ls -l | wc"
    int cmdType = 1; 
    int size = sizeof(line);
    char tempLine[size + 3];
    bool pipeSeen = false;
    for (int i = 0; i < size; i++) {
        if (line[i] == '|' && line[i - 1] != ' ') {
            tempLine[i]     = ' ';
            tempLine[i + 1] = '|';
            tempLine[i + 2] = ' ';
            pipeSeen = true;
        } else {
            if (pipeSeen == true)
                tempLine[i + 2] = line[i];
            else
                tempLine[i] = line[i];
        }
    }

    if (pipeSeen == true) {
        tempLine[size + 2] = '\0';
        line = tempLine; // change "ls -l|ls to ls -l | wc"
    }
    /* parse line and store it in argv */
    while (*line) {
        while (*line == ' ')
            *line++ = '\0';

        //Figure out what type of command we may have
        if (*line == '<')
            cmdType = (cmdType == 3) ? 5 : 2;
        else if (*line == '>' )
            cmdType = (cmdType == 2) ? 5 : 3;
        else if (*line == '|')
            cmdType = 4;

        *argv++ = line;
        while (*line != '\0' && *line != ' ' && *line != '\t' && *line != '\n')
            line++;
    }
    *argv = '\0';
    return cmdType;
}

void parseCmdWithPipe(char **argv) {
    int size = getCmdSize(argv);
    char val[1];
    int pipePosition = 0;
    for (int i = 0; i < size; i++) {
        strcpy(val, argv[i]);
        if (val[0] == '|') {
            pipePosition = i;
            break;
        }
    }

    char *argOne[pipePosition + 1];
    for (int i = 0; i < pipePosition; i++) {
        argOne[i] = argv[i];
    }
    argOne[pipePosition] = '\0';

    char *argTwo[size - pipePosition];
    for (int i = 0; i < (size - pipePosition); i++) {
        argTwo[i] = argv[i + pipePosition + 1];
    }
    argTwo[size - pipePosition - 1] = '\0';

    int pfd[2], pid;
    if (pipe(pfd) == 1)
        syserror("Could Not create a pipe");

    switch (pid = fork()) {
      case -1:
        syserror( "Fork Failed" );
      case 0:
        if (dup2(pfd[0], 0) == -1|| close (pfd[0]) == -1 || close (pfd[1]) == -1)
            syserror("Failed to run dup2 or close pfd in second child");
        execvp(argTwo[0], argTwo);
        syserror("execvp unsuccessful in 2nd child");
    }
     ....

我希望 "ls -l|wc" 给我相同的结果 "ls -l | wc" 给我

11      92     597

但实际输出是

execvp unsuccessful in 2nd child
(No such file or directory)

Answer 1

主要问题是int size = sizeof(line);它不计算 line 指向的字符串的大小和长度。 , 但仅评估为 char * 的大小.

你应该写int size = strlen(line);并且可能不会调用此变量 size ，但是 len相反。

代码太复杂，你不应该尝试在|两边插入空格符号，顺便说一句，你没有对 < 做同样的事情和 > .