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

#define BUF_SIZE 1024

/* Error and die. */
void croak(char *msg, int syserr)
{
	fprintf(stderr, "%s", msg);
	if(syserr) fprintf(stderr, ": %s", strerror(errno));
	fprintf(stderr, "\n");
	exit(1);
}

int main(int argc, char **argv)
{
	int infile, outfile;		/* Input and output file descrs. */

	if(argc != 3) croak("Need three args.", 0);
	
	/* Open the input file to read. */
	infile = open(argv[1], O_RDONLY);
	if(infile < 0) croak("Input file open", 1);

	/* Open output file, writable, truncate existing content, or create
	   if not. */
	outfile = open(argv[2], O_WRONLY | O_CREAT | O_TRUNC, 0777);
	if(infile < 0) croak("Output file open", 1);

	/* Copy the file */
	while(1) {
		char buf[BUF_SIZE];

		/* Read, return number of bytes read. */
		int nread = read(infile, buf, BUF_SIZE);

		/* Negative return indicates an error. */
		if(nread < 0) croak("Read input", 1);

		/* Zero return indicates EOF. */
		if(nread == 0) break;

		/* Write the amout of data read. */
		if(write(outfile, buf, nread) < 0) 
			croak("Write output", 1);
	}

	/* All done. */
	close(infile);
	close(outfile);
}