linuxshell.c

Linux中Shell的几条简单命令的实现,基本框架已经搭好了

/*    By Shoarh
(1)   pid [-p]    to get current process pid or parent process pid with parameter -p
(2)   cd          change derectory
(3)   pwd         current work derectory
(4)   logout      exit shell  
(5)   :           Use token : to execute every instruct by order
     
      [Normal Expression]
      instruction  -> pid [-p] | cd [..] [directory] | pwd | logout | [OR MORE]
      format       -> format : instruction | instruction 
                  
      You can use Multi-Instruction,each instructin separate by token :
      e.g ls -l : cd .. : pid -p : cd : pwd : ls -l : logout : ps -a 
      If logout is executed , the instruction after logout will now be executed */

#include <stdio.h>
#include <string.h>
#include <signal.h>
#include <ctype.h>
#include <unistd.h>
#define ARGNUM 20   //number of arg
#define ARGLEN 30   //length of each arg
#define BSIZE 255   //size of buffer

char inputbuffer[BSIZE];    //buffer of input
char argbuf[ARGNUM][ARGLEN];//get each arg
int indexnum;               //index arg position
char* arglist[ARGNUM];      //number of arg to be store in arglist
char* currentpos;           //current position of buffer
char defaultpath[255];      //default current path
int multi;                  //is multi-instruct

void cdcommand();
void pidcommand(int);

char getarg(char* c)//get token
{
	int i=0;  //each character of arg
        for(i=0;!isspace(*c);i++,c++,currentpos++)
	{      
           argbuf[indexnum][i]=*c;
	}
           argbuf[indexnum][i]='\0';
           arglist[indexnum]=argbuf[indexnum];//from argbuf to arglist
           indexnum++;
	while(isspace(*currentpos))
	{
           currentpos++;
	}
	if(*currentpos=='\0') return '\0';
	return *currentpos;
}

int exec(char *arglist[])//execute
{
        pid_t pid;int exitstatues;
	pid=fork();
	switch(pid) 
	{
		case -1: perror("fork failed");
			 exit(1);
		case 0:  execvp(arglist[0],arglist);
                         perror("execvp failed");
                         exit(1);
		default: while(wait(&exitstatues)!=pid) ;
	}
}

void conver()
{       
	indexnum=0;
	printf("\n&");
	memset(inputbuffer,' ',sizeof(inputbuffer));//clear inputbuffer
	fgets(inputbuffer,BSIZE,stdin);
	currentpos=inputbuffer;      //point to beginning of buffer
	if(*currentpos==':') conver();
	while(isspace(*currentpos))
	{
		currentpos++;
	}
	while(*currentpos!='\0')
	{      
		if(*currentpos==':')
		{  
			multi=1;
			arglist[indexnum]='\0';
			frame();
			*currentpos++;
			while(isspace(*currentpos)) *currentpos++; 
			indexnum=0; printf("\n");
			getarg(currentpos);
		}
		else
		{ 
			multi=0;
			getarg(currentpos);
		}
	}
	multi=0;
	arglist[indexnum]='\0';
}

int frame()
{
	    while( strcmp(arglist[0],"logout")!=0 || arglist[1]!=NULL )
            {       
                       int arglen=strlen(arglist[0]);
                       if(strcmp(arglist[0],"cd")==0)             //cd
                       {      
                             if((arglist[0][arglen+1])=='\0'&& arglist[1]==NULL)
                             {
                                  arglist[1]=defaultpath;
                                  cdcommand();
                             }
                             else  cdcommand();
                        }
                        else if(strcmp(arglist[0],"pid")==0)     //pid
                        {
                             if((arglist[0][arglen+1])=='\0'&& arglist[1]==NULL)     
                             pidcommand(0);
                             else if(strcmp(arglist[1],"-p")==0)//get parent pid
                             pidcommand(1);
                             else printf("Command Error!\n");
                        }
                        else
                        {
                             exec(arglist); 
                        }
                    if(multi) break;
                    else
                    {  
                       conver();
                       while(arglist[0]==NULL) conver();
                    }
            }
            if( strcmp(arglist[0],"logout")==0 ) exit(0);
}

main()
{
        getcwd(defaultpath,255);  //get current default path
        while(arglist[0]==NULL) 
        conver();
        frame();
}

void cdcommand()
{
        char curpath[255];
//	printf("Excuting cd command now!\n");
	if((int*)(chdir(arglist[1])==-1)) perror("Chdir directory Error!");
        getcwd(curpath,255);
 	printf("Current work directory: %s\n",curpath);
}
void pidcommand(int p)
{
//	printf("Excuting pid command now!\n");
	printf("Current process pid is %d\n",getpid());
	if(p) printf("Parent process pid is %d\n",getppid());
}