shell.c

在Linux环境下模拟shell 操作系统实验

/******************************
include files
*******************************/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/wait.h>

/*****************************
string structure
*****************************/
struct mystr {
  int length;
  char *content;
};

int k,is_back = 0;
char buffer[50];
char *argc;
char *argv[20];

/*****************************
print notice
use get_current_dir_name()
******************************/
void print_notice(void) {
  int path;
  path = get_current_dir_name();
  printf("@%s>",path);
}

/*****************************
get user's input
store the input in the buf string
******************************/
struct mystr get_user_instruction(void) {
  int i=0;
  char ch;
  char buf[80];
  struct mystr temp;

  scanf("%c",&ch);
  while(ch!='\n'&&i<50) {
    buf[i++]=ch;
    scanf("%c",&ch);
  }//while

  if(i>=80) {
    printf("instruction too long\n");
    i=0;
  }
  buf[i]='\0';
  temp.length=i;
  temp.content=buf;
  return temp;
}
 
/*****************************
analys instruction
split the string into *arg[]
return arg
*****************************/
void analy_instruct(struct mystr temp) {
  int i,j;
  k=0;
  char input[100];

  int li_inputlen=temp.length;
  strcpy(input,temp.content);

  for(i=0,j=0;i<=li_inputlen;i++) {
	   if(input[i]==' '||input[i]=='\t'||input[i]=='\0') {
		   if(j==0) continue;
		   else {
			   buffer[j++] = '\0';
			   if(k==0) {
				   argc = (char *) malloc (sizeof(char)*j);
				   strcpy(argc,buffer);
			   }
			   argv[k] = (char *) malloc(sizeof(char)*j);
			   strcpy(argv[k],buffer);
			   j=0;
			   k++;
		   }
	   }else {
		   if(input[i] == '&' && input[i+1] == '\0') {
			   is_back = 1;
			   continue;
		   }
		   buffer[j++] = input[i];
	   }
  }
}

/****************************
****************************/
int is_fileexist(char *c) {
  char *path,*p;
  int i=0;
  path = getenv("PATH");
  p=path;
  while(*p !='\0') {
    if(*p != ':')
      buffer[i++] = *p;
    else {
      buffer[i++] = '/';
      buffer[i] = '\0';
      strcat(buffer,c);
      if(access(buffer,F_OK) == 0)
        return 0;
      else 
        i = 0;
    }
    p++;
  }
  return -1;
}

/*****************************
*****************************/
void find_file(void) {
  if(strcmp(argc,"quit") == 0)
    printf("bye-bye\n");
  else {
	  argv[k] = (char *)0;
	  if(is_fileexist(argc) == -1)
		  printf("This command is not found!\n");
  }
}

/*****************************
*****************************/
void exe_instruct(void) {
  pid_t pid;
  int status;
  if((pid = fork()) == 0)
    execv(buffer,argv);
  else 
    if(is_back == 0)
      waitpid(pid,&status,0);
}

/*****************************
main
******************************/
int main () {
  struct mystr str;
  while(1) {
	  print_notice();
	  str = get_user_instruction();
	  if(str.length!=0) {
		  analy_instruct(str);
		  find_file();
		  if(strcmp(argc,"quit")==0)break;
		  exe_instruct();
	  }
  }
  return 0;
}