CS456 - Systems Programming Spring 2023

Displaying ./code/h1/copy.c

/*

implementing a version of the "cp" command using Linux System Calls

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

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

	if(argc < 3){  //prints usage statement to stderr if not enough arguments
		//file descriptor 2 is stderr
		//string is 41 bytes long
		write(2,"Usage: copy source_file destination_file\n", 41);
		return 1; //since we're only using system calls, well return 1 to exit the program
	}

	
	int src; //declares file descriptor for source file 
    src = open(argv[1], O_RDONLY); 			 //open the source file specified by user (YOU DO THIS)


	//check the return value of open here (YOU DO THIS)
		//if it is -1, use write to print a statement to stderr (which file descriptor is that?)
		//then return a value of -1 to exit the program 
    if(src == -1){
        write(2, "open failed\n", 12);
        return -1;
    }

	
	//Using the system call fstat to get the size of the file
	int size;			  //declare size variable
	struct stat st;       //needed so we can use stat
	fstat(src, &st);      //accessing the stat struct
	size = st.st_size;    //getting file size

	int dst; //declare a file descriptor for the destination file
	dst = open(argv[2], O_CREAT | O_WRONLY | O_TRUNC, 0644);	     //open the destination file for writing (YOU DO THIS)
		     	//if the file doesn't exist, create it
		     	//if it does exist, truncate it	(in other words, we're overwriting the contents)
                //also set permissions to 0644 


	char srcbuf[size+1]; //setting up the buffer to read into
						 //making buffer size 1 byte larger than file size, just to be safe

	// DO THESE TWO THINGS
	//use read to read the file contents into the buffer we just set up
	//then use write to write whatever is in the buffer we just read into to the destination file
    read(src, srcbuf, size);
	write(dst, srcbuf, size);
					 
	//we're done, so close the file descriptors
	close(src);
	close(dst);

	return 0;

	

}