Prints a HID device to stdout

printhid.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <fcntl.h>
#include <dirent.h>
#include <linux/input.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/select.h>
#include <sys/time.h>
#include <sys/ioctl.h>
#include <termios.h>
#include <signal.h>

void handler (int sig)
{
    printf ("\nexiting...(%d)\n", sig);
    exit(0);
}

void perror_exit (char *error)
{
    perror(error);
    handler(9);
}

int main (int argc, char *argv[])
{
    struct input_event ev[64];
    int fd, rd, value, size = sizeof (struct input_event);
    char name[256] = "Unknown";
    char *device = NULL;

    //Setup check
    if (argv[1] == NULL){
        fprintf(stderr, "Please specify (on the command line) the path to the dev event interface device\n");
        exit (0);
    }

    if ((getuid ()) != 0)
        fprintf (stderr, "You are not root! This may not work...\n");

    if (argc > 1)
        device = argv[1];

    //Open Device
    if ((fd = open (device, O_RDONLY)) == -1) {
        fprintf (stderr, "%s is not a vaild device.\n", device);
        exit(1);
    }
        
    //Print Device Name
    ioctl (fd, EVIOCGNAME (sizeof (name)), name);
    fprintf (stderr, "Reading From : %s (%s)\n", device, name);
    
    //Stop propagation of the event
    ioctl (fd, EVIOCGRAB, 1);

    while (1) {
        if ((rd = read (fd, ev, size * 64)) < size)
            perror_exit("read()");

        value = ev[0].value;
        
        if (value != ' ' && ev[1].value == 1 && ev[1].type == 1){ // Only read the key press event
            int val = ev[1].code - 1;
            if (val == 27) {
                fprintf (stdout, "\n");
            }else{
                fprintf (stdout, "%d", val);
            }
            fflush(stdout);
        }
    }
    return 0;
}