CS456 - Systems Programming Spring 2025

Displaying ./code/Jan30/myCat_sys.c

/*

implementing a version of the "cat" 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 < 2){  //prints usage statement to stderr if not enough arguments
		//file descriptor 2 is stderr
		write(2,"Usage: mycat filename\n", 22);
		return 1;
	}

	//declares file descriptor, tries to open file specified by user
	int fd; 
	fd = open(argv[1], O_RDONLY);

	//if file does not exist, print usage statement to stderr and exit the program
	if(fd == -1){
		write(2,"open failed\n", 12);
		return -1;
	}

	//if we get here, we've sucessfully opened the program
	
	//getting the size of the file
	int size;
	struct stat st; //needed so we can use stat
	fstat(fd, &st);      //accessing the stat struct
	size = st.st_size;   //getting file size

	//printf("%d\n", size); //for debugging purposes only

	char buf[size+1]; //setting up the buffer to read into

	read(fd, buf, size); //reading the file contents into a buffer
						 //read returns the number of bytes read

	write(1, buf, size); //writing the file contents to stdout
						 // file descriptor 1 is stdout

	//we are done now, so close the file descriptor
	close(fd);
	return 0;

	

}