unix_简单shell实现

#include  " apue.h "
#include  < sys / wait.h >
extern  char  ** environ;
static void sign_Int( int  signnal)
{printf( " Be interrupted\n%% " );}
static void sign_Quit( int  signnal)
{printf( " quit\n%% " );
}

int  
main(void)
{
   
    char  * argv[ 20 ];
    pid_t pid;
     int  status;
     if (signal(SIGINT,sign_Int) == SIG_ERR)
       err_sys( " signal error\n " );
     if (signal(SIGQUIT,sign_Quit) == SIG_ERR)
         err_sys( " signal error\n " );
    printf( " %% " );
     while  ( 1 )
    {        char buf[MAXLINE];
              int  index = 0 ,i = 0 ;
            if (fgets(buf,MAXLINE,stdin) == NULL )
             break;  
         while ( buf[i] ! =   ' \0'&&buf[i]!='\n' )
        {
            if (buf[i] ! =   '  ' )
           {  
               argv[index] =  buf + i;
               index ++ ;
                for (;buf[i]! =   '  '&&buf[i]!='\n';i++);
                if (buf[i] == ' \n')
               break;               
               buf[i] = ' \0';
                i ++ ;
                 while (buf[i] == '  ') 
                       i ++ ; 
           }  
        } 
        buf[i] = ' \0';
        argv[index]  =   NULL ;
         if ((pid  =  fork() )  <   0  ) 
           err_sys( " fork error\n " );
         else   if ( pid  ==   0  )
        {
           execve(argv[ 0 ],argv,environ);
           err_ret( " coundn't execute:%s " ,argv[ 0 ]);           
            exit ( 127 );
          }
         if (( pid  =  waitpid(pid, & status, 0 ))  <   0 )
           err_sys( " waitpid error\n " );
          printf( " %% " ); 
     }
      exit ( 0 );
}