#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#define MAX_LINE 80 /* 80 chars per line, per command, should be enough. */
/**
* setup() reads in the next command line, separating it into distinct tokens
* using whitespace as delimiters. It also sets the args parameter as a
* null-terminated string.
*/
typedef struct list
{
int num;
int *ptr;
struct history * next;
}history;
void setup(char inputBuffer[], char *args[],int *background)
{
int length, /* Number of characters in the command line */
i, /* Loop index for 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){
perror("error reading 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] = ' '; /* 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] = ' ';
args[ct] = NULL; /* no more arguments to this command */
break;
case '&':
*background = 1;
inputBuffer[i] = ' ';
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 */
while (1){ /* program terminates normally inside setup */
background = 0;
printf("CSE2431Sh->");
fflush(0);
setup(inputBuffer, args, &background); /* get next command */
/* 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. */
int child_pid;
int status;
int ph;
history *history = NULL;
child_pid = fork();
if(child_pid == 0)
{
ph++;
history->num = ph;
history->ptr = args;
execvp(args[0],args);
/* If execvp returns, it must have failed. */
printf("Execvp Failedn");
exit(0);
}
else
{
if(background == 0)
{
int parent_pid;
while ((parent_pid = wait(&status)) != -1 && parent_$
;
}
else
{
setup(inputBuffer, args, &background);
}
}
}
}
我正在尝试向外壳添加历史记录功能。外壳应该存储命令和编号。它还应该能够恢复最后 8 个命令以再次运行。例如，如果用户已经输入了35个命令，则28-35应该能够恢复。用户应该能够通过键入历史记录来查看最后 8 个命令，并通过键入 x num 来运行上一个命令，其中 num 是命令的编号，或 xr 来运行最新的命令。我的计划是使用链表，但我遇到了麻烦，只有几个小时来完成它。
正如我们在上一篇文章中所推荐的：
首先，您另外存储长度的
linked list怎么样 和列表的最后一项？这些项目是来自您的命令 输入缓冲区。