Microshell实施，管道问题

Question

我目前正致力于使用Linux系统调用的microshell的实现。我的大部分代码都在那里工作，但是当我尝试将一个命令传递给另一个时，我遇到了一个问题。当我输入more myfile || grep Dog时，我应该将Dog显示回来，但我没有显示任何内容，当我尝试管道时，这适用于任何事情。像cat myfile这样的单个命令工作得很好。我只能假设我目前正在尝试使用pipe的方式有问题，但我似乎无法弄清楚是什么导致了它。

修改：||实际上没有进行管道操作，在第一个while循环中搜索||的用户输入以指示用户想要执行管。然后从那里开始从变量mainPipe创建管道。

以下是我的名为myfile的文件。

Nope
Illinois
USA
Dog

这是我的代码，

#include <sys/types.h>
#include <sys/wait.h>
#include <stdio.h>
#include <string.h>
#include <iostream>
#include <sstream>
#include <stdlib.h>
#include <sys/utsname.h>
#include <unistd.h>
using namespace std;

#define BUFFER_SIZE 1024
#define PIPE_SIZE 2

void const firstCommandWork(int _pipe[], char * command[], const bool pipeExists);
void const secondCommandWork(int _pipe[], char * command2[]);

int main() {
    char *userCommand[BUFFER_SIZE],   //char array ptrs that will hold the user desired command
        *userCommand2[BUFFER_SIZE],   //Note to self: maybe NULL first few to clear out space.
        buffer[BUFFER_SIZE];      //buffer that will hold user input
    int status,             //status of the child process in it's parents process
        status2;
    int mainPipe[PIPE_SIZE];  //pipe variable
    pid_t fork1,            //fork variables
        fork2;

    cout << "480shell>";     //shell header

    while (fgets(buffer, BUFFER_SIZE, stdin) != NULL) {     //continue to get input from user until none is entered
        bool userWantsPipe = false;      //variable that will be set to true if the user wishes to use pipe command

        buffer[strlen(buffer) -1] = 0;   //remove last character in buffer

        int tokenIndex = 0;              //used to seperate tokens
        char *bufferPtr;                 //char array to hold saved token made by strok
        bufferPtr = strtok(buffer, " "); //gets first command from buffer up to a white space and saves it in bufferPtr

        while(bufferPtr != NULL) {       //continue as long as there's something in the bufferPtr
            if( (strcmp( bufferPtr, "q" ) == 0) || (strcmp( bufferPtr, "quit" ) == 0) ) {      //if user entered "q" or "quit, exit program
                cout << "Exiting.." << endl << endl;
                return 0;
            }

            if(strcmp( bufferPtr, "||" ) == 0) {     //if user entered "||" (meaning they wish to use pipe)
                userWantsPipe = true;                //set userWantsPipe to true
                bufferPtr = strtok(NULL, " "); 
            }

            if(!userWantsPipe) {                      //if user has not entered "||" (meaning they do not wish to pipe)
                userCommand[tokenIndex] = bufferPtr;  //grab first command (in the bufferPtr) and store it in the first user command variable @ tokenIndex (0)
                bufferPtr = strtok(NULL, " ");
                tokenIndex++;                         //add one to tokenIndex, to represent one command already gotten
            }
            else {                                    //user has entered "||" (meaning they wish to pipe)
                userCommand2[tokenIndex] = bufferPtr; //grab first command (in the bufferPtr) and store it in the first user command variable @ tokenIndex (0)
                bufferPtr = strtok(NULL, " ");
                tokenIndex++;                         //add one to tokenIndex, to represent one command already gotten
                int val = pipe(mainPipe);                        //create pipe from pipe variable

                if(val == -1) {                     
                    cout << "Failed: Pipe. Exiting..." << endl; 
                }
            }
        }

        fork1 = fork();    //create first fork
        if(fork1 < 0) {   //first fork has failed, exit program
            cerr << "Failed: First Fork. Exiting..." << endl;
            return -1;
        }
        if(fork1 == 0) {   //child process of first fork
            firstCommandWork(mainPipe, userCommand, userWantsPipe);
        }

        if(userWantsPipe) {      //if the user used the pipe command
            fork2 = fork();      //create second fork
            if(fork2 == 0) {     //child process of second fork
                secondCommandWork(mainPipe, userCommand2);
            }
            if(fork2 < 0) {      //second fork has failed, exit program
                cerr << "Failed: Second Fork. Exiting..." << endl << endl;
                return -1;
            }
        }

        if(userWantsPipe) {     //if the user used the pipe command
          close(mainPipe[0]);    //close ends of the pipe
          close(mainPipe[1]);
        }

        fork1 = waitpid(fork1, &status, 0);     //wait for first child to execute
        if(fork1 < 0) {                         //waiting on first child to finish has failed, exit program
            cerr << "Failed: Waiting First Child. Exiting..." << endl;
            return -1;
        }

        if(userWantsPipe) {                         //if the user used the pipe command
            fork2 = waitpid(fork2, &status2, 0);    //wait for second child to execute
            if (fork2 < 0) {                        //waiting on second child to finish has failed, exit program
                cerr << "Failed: Waiting Second Child. Exiting..." << endl << endl;
                return -1;
            }
        }
        cout << "480shell>";                        //shell header
      }
      return 0;
} 

/*********************************************************
void const firstCommandWork(int [], char* [], const bool)
returns: nothing
arguments: 1) a int array representing a pipe (_pipe)
    2) a ptr to a char array (command), holds the commands entered by the user
    3) a constant bool (pipeExists), holds true if user used pipe command
        otherwise holds false
use: ** used to execute the first command entered by user **
    first, if the user wanted to use the pipe command (pipeExists will be true in this case)
        we will first call dup2() on the pipe (_pipe) to create copy of the file descriptor
        then we will close the end of the pipe (_pipe)  
    second, then we will execute the command @ location 0 (this will be the first command) in command array
        if the command has failed, display a message, exit with -1
*********************************************************/
void const firstCommandWork(int _pipe[], char *command[], const bool pipeExists) {
    if(pipeExists) {
        dup2(_pipe[1], 1);
        close(_pipe[0]);
    }

    int val = execvp(command[0], command); //store value of whether or not command could execute

    if(val < 0) {                          //couldn't execute command, display message, exit with a value of -1
        cerr << "Error: Could Not Execute First Command!" << endl;
        exit(-1);
    }
}

/*********************************************************
void const secondCommandWork(int [], char* [])
returns: nothing
arguments: 1) a int array representing a pipe (_pipe)
    2) a ptr to a char array (command2), holds the commands entered by the user
use: ** used to execute the second command entered by user **
    first, we will first call dup2() on the pipe (_pipe) to create copy of the file descriptor
        then we will close the end of the pipe (_pipe)  
    second, then we will execute the command @ location 0 (this will be the second command) in command2 array
        if the command has failed, display a message, exit with -1
*********************************************************/
void const secondCommandWork(int _pipe[], char *command2[]) {
    dup2(_pipe[0], 0);
    close(_pipe[1]);

    int val = execvp(command2[0], command2); //store value of whether or not command could execute

    if(val < 0) {                            //couldn't execute command, display message, exit with a value of -1
        cerr << "Error: Could Not Execute Second Command!" << endl;
        exit(-1);
    }
}

Answer 1

在第二个 constructor(private activatedRoute: ActivatedRoute) { } ngOnInit() { this.activatedRoute.queryParams.subscribe((data) => { console.log(data); }); } 循环中向tokenIndex = 0;正文添加了else。修复问题。