mycrontab.c

Cron的实现 UNIX 下设计编写中小型程序的能力

#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>
#include <string.h>

int main(int argc,char* argv[])
{
	int fd1,fd2,length,pid;
	char textfile[200],vi[50]="vi ";
	if(argc!=2&&argc!=3)
    	{
			printf("usage:\n%s <filename>\n%s <filename> {-l|-r|-e}\n",argv[0],argv[0]);
        	exit(1);
    	}
	else if(argc==2)
	{
		printf("Using the new input task file as crontab file\n");
		fd1=open(argv[1],O_RDONLY,S_IROTH|S_IWOTH);        //command of mycrontab file 
		system("touch j03031.cron");
		fd2=open(" j03031.cron",O_WRONLY,S_IROTH|S_IWOTH);
		length=read(fd1,textfile,200);
		if(write(fd2,textfile,length)<0)
		{
			printf("can't %s %s\n",argv[0],argv[1]);
			exit(1);
		}
		exit(0);
	}
	else if(argc==3)		//there are 3 parameters
	{
		if(strcmp(argv[2],"-l")==0)	//display the current crontab file
		{
			printf("The contant of the crontab file is as following:\n");
			system("cat  j03031.cron");
			exit(0);
		}
		else if(strcmp(argv[2],"-r")==0)//remove the current crontab file
		{
			system("rm  j03031.cron");
			printf("The crontab file has been removed\n");
			exit(0);
		}
		else if(strcmp(argv[2],"-e")==0)
		{

			if((pid=fork())<0)
			{

				printf("Fork vi process fail\n");
				exit(1);
			}
			else if(pid>0)		//create a child process to execute the editor
			{
				strcat(vi,argv[1]);
				execl("/bin/sh","sh","-c",vi,(char *)0);
			}
			waitpid(pid,NULL,0);
			fd1 = open(argv[1],O_RDONLY,S_IROTH|S_IWOTH);
			system("rm  j03031.cron");
			system("touch  j03031.cron");
			fd2 = open(" j03031.cron",O_WRONLY,S_IROTH|S_IWOTH);
			length=read(fd1,textfile,500);
			if(write(fd2,textfile,length)<0)
			{
				fprintf(stderr,"can't %s %s\n",argv[0],argv[1]);
				exit(1);
			}
 

			exit(0);
		}
		else		//parameter error
		{
			printf("usage:\n%s <filename>\n%s <filename> {-l|-r|-e}\n",argv[0],argv[0]);
			exit(1);
		}
	}
}