Salehin_23_7

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

#define BUFFER_SIZE 1024

int main(int argc, char* argv[]){
	int inputFD, outputFD;
	ssize_t retIn, retOut;
	char buffer[BUFFER_SIZE], userInput;

	if(argc==1){
		printf("Specify output file name at least\n");
		return 0;
	}
	else{
		outputFD=open(argv[1],O_WRONLY|O_CREAT|O_TRUNC, 766);
		if(outputFD==-1){
			perror("Error!!!");
			return 0;
		}

		if(argc==2){
			while((retIn=read(STDIN_FILENO,&buffer,BUFFER_SIZE))>0){
				retOut=write(outputFD,&buffer,(ssize_t)retIn);
				if(retOut!=retIn){
					perror("Write");
					return 0;
				}
			}
		}
		else{
			int i;
			for(i=2;i<argc;i++){
				inputFD=open(argv[i],O_RDONLY);
				if(inputFD==-1){
					perror("Error!!!");
					return 0;
				}
				while((retIn=read(inputFD,&buffer,BUFFER_SIZE))>0){
					retOut=write(outputFD,&buffer,(ssize_t)retIn);
					if(retOut!=retIn){
						perror("Write");
						return 0;
					}
				}
				close(inputFD);
			}
		}
		close(outputFD);
	}


	return 0;
}