myshell.c

一个shell程序可以实现管道

/*BY Dai Qieyun
 *   Chen Xinwei
 *   Dai Wei
*/

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

extern char **getline();

main() {
  int i;
  char **args;
  int pid;
  int stat_val;
  int isRedirect;
  int isPipe;
  int isBack;
  int position; 

  printf("Welcome to MyShell ^_^\n");

  while(1) {
    
    isRedirect=0;
    isPipe=0;
    position=0;

    printf("MyShell>>");
    args = getline();

    for(i = 0; args[i] != NULL; i++){    //testing whether the command is redirection or pipe
      if(!strcmp(args[i],"<")||!strcmp(args[i],">"))
	{
	  isRedirect=1;
	  position=i;
	}
      if(!strcmp(args[i],"|")){
	  isPipe=1;
	  position=i;
	}
    }
    
    if(args[0]==NULL); //empty command

    else if(!strcmp(args[i-1],"&")){//background execution
      args[i-1] = NULL;
      pid=fork();//bulid a runback process,and don't eliminate the parent process
      if(pid==-1) { 
         perror("Failed to fork");
         return 1;
      }
      if(pid == 0){
         if(setsid() == -1)
            perror("Child faild to become a session leader");
         else{ 
            execvp(args[0],args);
            printf("Command not found in PATH\n");
            exit(0);
         }
         return 1;
      }
    }

    else if(isPipe){  //pipe
	pid_t child,gChild;
	int file_pipes[2];	
	char **command;
        command=&args[position+1];
	args[position]=NULL;
        child=fork();
        switch(child){
            case -1:
              perror("Fork Failed\n");
              exit(-1);

            case 0:
              if(!pipe(file_pipes)){
                  gChild=fork();
                  switch(gChild){
                     case -1:
                        fprintf(stderr,"Fork Failed\n");
                        exit(-1);

                     case 0:           //the grandchild process,writing to the pipe
                        
                        close(1);
                        dup2(file_pipes[1],1);
                        close(file_pipes[1]);
                        close(file_pipes[0]);
                        execvp(args[0],args);
                        printf("Command not found in PATH\n");
                        exit(0);    




                     default:         //the child process, reading from the pipe
                        
                        close(0);
                        dup(file_pipes[0]);
                        close(file_pipes[0]);
                        close(file_pipes[1]);
                        execvp(command[0],command);
                        printf("Command not found in PATH\n");
                        exit(0);                     
                    }
              }  
              default:
                   waitpid(child,&stat_val,0);
                   if(!WIFEXITED(stat_val))
                        printf("Child terminated abnormally\n");
         }
                          
    }

    else if(!strcmp(args[0],"exit")) //the exit command
        exit(0);

    
    else if(!strcmp(args[0],"add")){ //the add command
        pid=fork();
        
        switch(pid){

           int i;
           int result;
        
           case -1:
              perror("Fork Failed\n");
              exit(-1);
           
           case 0:
              if(isRedirect){
                 char *fileName;
		 fileName=args[position+1];
		 args[position]=NULL;
		 if(!freopen(fileName,"w",stdout)){ //Redirect the add result to file
		    fprintf(stderr,"could not redirect stdout to file %s\n",fileName);
		    exit(2);
	         }
              }    
              result=add(args);
              for(i=1;args[i+1]!=NULL;i++)
                 printf("%s+",args[i]);
              printf("%s=%d\n",args[i],result);
              exit(0);
           
           default:
              wait(&stat_val);
              if(!WIFEXITED(stat_val))
                  printf("Error:child terminated abnormally\n");
  
        }
   }

   else if(!strcmp(args[0],"args")){ //the args command
       pid=fork();

       switch(pid){

         case -1:
            perror("Fork Failed\n");
            exit(-1);

         case 0:
            if(isRedirect){
               char *fileName;
	       fileName=args[position+1];
	       args[position]=NULL;
		 if(!freopen(fileName,"w",stdout)){ //redirect args result to file
		    fprintf(stderr,"could not redirect stdout to file %s\n",fileName);
		    exit(2);
	      }
            }    
            arg(args);
            exit(0);

         default:
            wait(&stat_val);
            if(!WIFEXITED(stat_val))
                printf("Error:child terminated abnormally\n");
      }
   }

   else if(!strcmp(args[0],"search")){
        printf("%d found\n",search(args));
   }



   else {   //the rest of the cases
        pid=fork();

        switch(pid){

            case -1:
              perror("Fork Failed\n");
              exit(-1);

            case 0:
              if(isRedirect){  //redirection
                 char *fileName;
		 fileName=args[position+1];
		 if(*args[position]=='>'){
		    args[position]=NULL;
		    if(!freopen(fileName,"w",stdout)){ //writing to file, closing standard out
			fprintf(stderr,"could not redirect stdout to file %s\n",fileName);
			exit(2);
		    }
		    execvp(args[0],args);
                    fprintf(stderr,"Command not found in PATH\n");
                    exit(0);
	         }    
	         else{
		    args[position]=NULL;
		    if(!freopen(fileName,"r",stdin)){ //reading rom file, closing standard in
		       fprintf(stderr,"could not redirect stdin to file %s\n",fileName);
		       exit(2);
		    }
		    execvp(args[0],args);
                    printf("Command not found in PATH\n");
                    exit(0);
		}
              }
              else{        
                   execvp(args[0],args);
                   printf("Command not found in PATH\n");
                   exit(0);
              }


            default:
              wait(&stat_val);
              if(!WIFEXITED(stat_val))
                  printf("Error:child terminated abnormally\n");
    
        }
     }
   }
}

int add(char**args)
{
   int sum=0; 
   int i;
   for(i=1;args[i]!=NULL;i++){
      if(args[i][0]=='0'&&args[i][1]!='\0'&&(args[i][1]=='x'||args[i][1]=='X'))
         sum+=hex(args[i]);
      else
         sum+=dec(args[i]);
   }
   return sum;
}

int dec(char* str){ //converting string notation of dec number to decimal int
   int num=0;
   int i;
   for(i=0;str[i]!='\0';i++){
     int digit=str[i]-'0';
       if(digit<0||digit>9){
         printf("Wrong with your input\n");
         exit(0);
       } 
     num=10*num+digit;
   }
   return num;
}



int getNumber(char a){ //converting char to number
   if('0'<=a&&a<='9')
     return a-'0';
   else if ('a'<=a&&a<='f')
     return 10+a-'a';
   else if('A'<=a&&a<='F')
     return 10+a-'A';
   else{
     printf("Wrong with your input\n");
     exit(0);
  }
} 

int hex(char* str){ //converting string notation of hex number to decimal int
   int num=0;
   int i;
   for(i=2;str[i]!='\0';i++){
     int digit=getNumber(str[i]);
       num=16*num+digit;
   }
   return num;
}

arg(char** args){
   char* result;
   int i;
   if(args[1]==NULL){
     printf("args=0");
     return;
   }
   for(i=1;args[i]!=NULL;i++);
   printf("argc=%d,args=",i-1);
   for(i=1;args[i+1]!=NULL;i++)
     printf("%s,",args[i]);
   printf("%s\n",args[i]);
}

int search(char ** args)  //search the file you give , count the times of the string you have given
{
    char*str=args[1];
    char*filename=args[2];
    printf("search \"%s\" in file %s\n",str,filename);
    int count=0;
    int c;
    int i=0;
    int len=strlen(str);
    FILE *fp;
    fp=fopen(filename,"r");

    while((c=fgetc(fp))!=EOF)
    {
        if(c==str[i])
        {
            if(++i==len)
            count++;
        }
        else
        {
            i=0;
        }
        }
    fclose(fp);
    return count;
}