Shell Programming and Scripting

/* listing - cpipe.c*/

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#define CLOSEALL()	close(pipefd[0]),close(pipefd[1])

int main(int argc,char *argv[]){
		int pipefd[2],fd;
		pid_t pid1,pid2;
		int result;
		
		if (argc < 2){
			printf("Argument Missing\nUsage: ./cpipe filename\n");
			exit(1);
		}

		if (pipe(pipefd) < 0){
			perror("pipe:");
			exit(1);
		}
		
		pid1 = fork();
		
		if(pid1==-1){
				perror("fork");
				exit(1);
			   }

	        else if(pid1==0){

				pid2 = fork();
				if(pid2 == -1){
					perror("fork");
					exit(1);
				}
				else if(pid2 == 0){
				dup2(pipefd[1],STDOUT_FILENO);
				CLOSEALL();
				if(execlp("/usr/bin/wc","wc","-l",argv[1],0)< 0){
					perror("execlp");
					exit(1);
				}
				}
		
				else{
				dup2(pipefd[0],STDIN_FILENO);
				if((fd = open("temp",O_RDWR|O_CREAT|O_TRUNC,0666))==-1){
				perror("open");
				exit(1);
				}
				dup2(fd,STDOUT_FILENO);
				CLOSEALL();
				close(fd);
				if(execlp("/usr/bin/awk","awk","-F"," ","{print $1}",0) < 0){
				perror("execlp");
				exit(1);
				}
		    	}
			}
		
		else{
			CLOSEALL();
			waitpid(pid1,NULL,0);
			FILE *fp = fopen("temp","r");
			fscanf(fp,"%d",&result);
			fclose(fp);
			//unlink("temp");
			printf("And the result is :: %d\n",result);
		    }

		return 0;
	 }