CS456 - Systems Programming Spring 2026

Displaying ./code/h2/concat.c

/*

we start with a simple version of the cat command, and will make some 
a few improvements. 

i've included below a header file i made myself called "extras.h" that currently
has two functions:

get_fdSize - takes a file descriptor, returns the size of the file
	int get_fdSize(int fd);

get_fdPerms - takes a file descriptor, returns the file permissions
	int get_fdPerms(int fd);

For this program, you will only need one of these (figure out which one!)

You will make the following improvements:

1. Currently, this is hardcoded to read up to 1024 bytes, change this so that it
   will read and write whatever the size of the file is

2. If more than 1 file is provided on the command line, print that file too
	Ex:
	> ./concat hello
	Will print the contents of the file "hello" to standard output

	> ./concat hello world
	Will print the contents of the file "hello" and the contents of the file 
	"world" to standard output

	If there is an error opening that file, just print an error message and skip
	printing it.  

Compile
> gcc -o concat concat.c

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

//including my own header file here
#include "extras.h"

int main(int argc, char **argv){

	//prints usage statement if required arguments are unavailable
	if(argc < 2){
		fprintf(stderr, "Usage: %s files ...\n", argv[0]);
		exit(1);
	}

	//declares file descriptor and opens source file for reading
	int src = open(argv[1], O_RDONLY);

	//check return value for errors
	if(src == -1){
		fprintf(stderr, "Error in %s: ", argv[1]);
		perror("open");
		exit(-1);
	}


	//creating arrays for buffer
	char buffer[1024];

	int data = read(src, buffer, 1024);

	write(1, buffer, data);

	close(src);

	return 0;

}