http://blog.csdn.net/lishuhuakai/article/details/11928055

#include <stdio.h>
#include <unistd.h>
#include <wait.h>
#define MAXLINE 80

void setup (char inputBuffer[], char *argv[])
{

    int i, j;
    char *p;
    i = 0;
    for (p = inputBuffer; ;p++)/*將字符命令一段一段拆分開來,如輸入ls -l,則argv[0]= "ls",argv[1]="-l",argv[2]=NULL
 
*/
    {
        argv[i++] = p;
        while (*p != ‘ ‘ && *p != ‘\0‘)
            p++;
        if (*p == ‘\0‘)
        {
            break;
        }
        *p = ‘\0‘;
       }
    argv[i] = NULL;/*最後一個參數須用空指針NULL作結束*/
    execvp (argv[0], argv);/*執行命令,argv[0]放著執行的命令，其余的argv放著參數*/
}



int main()
{

    
 
char inputBuffer[MAXLINE];
    char *argv[MAXLINE / 2 - 1];

    while (1)
    {
        printf ("COMMAND->");
          gets (inputBuffer);/*輸入命令*/
        setup (inputBuffer, argv);
                printf ("撲街！");
    }
    return 0;
}

#include <stdio.h>
#include <unistd.h>
//#define SIZE 20
 

#define MAXLINE 80
char *p;

void setup (char inputBuffer[], char *argv[])
{
    int i, j;
    i = 0;
    for (p = inputBuffer; ;p++)/*一個一個地將輸入字符分開*/
    {
        argv[i++] = p;
        while (*p != ‘ ‘ && *p != ‘\0‘)
            p++;
        if (*p == ‘\0‘)
        {
            break;
        }
        *p = ‘\0‘;
       }
    argv[i] = NULL;
    pid_t pid
    pid = fork();/*新建一個子進程*/
    if (pid == 0)/*對於子進程，執行輸入的命令*/
    {
     execvp (argv[0], argv);
     printf ("command not found\n");/*如果execvp執行失敗的話，會返回-1,也就是這句話會被執行*/
    }

    else if( pid > 0 )/*對於父進程，等待*/
    {
     wait(NULL);/*父進程等待子進程執行完*/
    }

     else /*否則的話，就出錯了*/
     {
      printf ("fork error\n");
     }
}

int main()
{
    char inputBuffer[MAXLINE];
    char *argv[MAXLINE / 2 - 1];

    while (1)
    {
        printf ("COMMAND->");
          gets (inputBuffer);
        /*關於scanf和gets,scanf對於輸入的字符遇到空格或回車就結束了，而gets對於輸入的空格也接受*/
        setup (inputBuffer, argv);

    }
    return 0;
}

簡單shell實現