Question

我正在尝试跟踪shell中的最后10个命令，并让ctrl + c信号处理程序输出它们的数组。

显然这个数组只包含10个元素，总是输出10个;这只是暂时的，直到我得到正确的功能。

当我在shell历史记录中有多个命令时，它会以奇怪的顺序多次输出数组，其中一些输出比其他输出更多。我猜这是由子进程也调用处理程序引起的，但我不知道该做什么。

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <signal.h>
#include <string.h>
#include <errno.h>

#define MAX_LINE 80 /* 80 chars per line, per command, should be enough. */
#define BUFFER_SIZE 10

char buffer[BUFFER_SIZE][MAX_LINE];
//char buffer[BUFFER_SIZE];
int pos = 0;
int handleEvent = 0;

void handle_SIGINT()
{
   int i = 0;
   while (i < BUFFER_SIZE)
   {
      //printf("%d\n", i);
      write(STDOUT_FILENO, buffer[i], strlen(buffer[i]));
      printf("\n");
      i++;
   }
}


void setup(char inputBuffer[], char *args[],int *background)
{
    int length, /* # of characters in the command line */
    i,      /* loop index for accessing inputBuffer array */
    start,  /* index where beginning of next command parameter is */
    ct;     /* index of where to place the next parameter into args[] */

    ct = 0;

    /* read what the user enters on the command line */
    length = read(STDIN_FILENO, inputBuffer, MAX_LINE);  

    start = -1;
    if (length == 0)
        exit(0);            /* ^d was entered, end of user command stream */
    if ((length < 0) && (errno !=EINTR)){
        perror("error reading the command");
    exit(-1);           /* terminate with error code of -1 */
    }

    /* examine every character in the inputBuffer */
    for (i = 0; i < length; i++) { 
        switch (inputBuffer[i]){
        case ' ':
        case '\t' :               /* argument separators */
            if(start != -1){
                args[ct] = &inputBuffer[start];    /* set up pointer */
                ct++;
            }
            inputBuffer[i] = '\0'; /* add a null char; make a C string */
            start = -1;
            break;


        case '\n':                 /* should be the final char examined */
            if (start != -1){
                args[ct] = &inputBuffer[start];     
                ct++;
            }
            inputBuffer[i] = '\0';
            args[ct] = NULL; /* no more arguments to this command */
            break;

        case '&':
            *background = 1;
            inputBuffer[i] = '\0';
            break;

        default :             /* some other character */
            if (start == -1)
                start = i;
        } 
    }    
    args[ct] = NULL; /* just in case the input line was > 80 */
} 

int main(void)
{
    char inputBuffer[MAX_LINE]; /* buffer to hold the command entered */
    int background;             /* equals 1 if a command is followed by '&' */
    char *args[MAX_LINE/2+1];/* command line (of 80) has max of 40 arguments */

    /* set up the signal handler */
    struct sigaction handler;
    handler.sa_handler = handle_SIGINT;
    //handler.sa_flags = 0;
    //sigemptyset(&handler.sa_mask);
    sigaction(SIGINT, &handler, NULL);

    while (1){            /* Program terminates normally inside setup */
        background = 0;
    printf("COMMAND->");
        fflush(0);
        setup(inputBuffer, args, &background);       /* get next command */

    strcpy(buffer[pos], inputBuffer);
    pos++;

        int pid;
    int returnValue;

    pid = fork(); /* for a child process */

    if (pid < 0) { /* check if error occurred with child process */
      fprintf(stderr, "Fork Failed");
      return 1;
    } 
    else if (pid == 0) { /* child process */
      execvp(args[0], args);
    } 
    //else {
      if (background == 0){ /* check if the parent should wait */
        //wait(&returnValue);
        waitpid(pid, NULL, 0);
      }
   //}

    /* the steps are:
     (1) fork a child process using fork()
     (2) the child process will invoke execvp()
     (3) if background == 0, the parent will wait, 
    otherwise returns to the setup() function. */
    }
}

Answer 1

我至少看到两件事：

execvp将在出现错误时返回（例如，如果您尝试运行未知命令），因此需要在execvp之后添加一个return语句。
read不会读取字符串char的结尾，所以你需要像inputBuffer [length] ='\ 0';

此外，当您按Ctrl + C时，我认为您也会从read（）返回并将inputBuffer的最后一个值添加到历史记录中。

希望这有帮助。

当有人通过信号处理进入“CTRL-C”时，在我的shell中的历史缓冲区中输出最后10个命令

1 个答案: