backlight control program for linux on dell latitude 3510

backlight.c

#include <stdio.h>
#include <stdlib.h>

#define BRIGHTNESS_FILE "/sys/class/backlight/intel_backlight/brightness"
#define MAX_BRIGHTNESS 120000

static void __attribute__((noreturn)) die(const char *msg) {
    printf("%s\n", msg);
    exit(EXIT_FAILURE);
}

int main(int argc, char *argv[]) {
    if (argc != 2) {
        die("Please provide an argument.");
    }

    const char direction = argv[1][0];
    if (direction != '+' && direction != '-') {
        die("Please provide a direction to move the brightness in.");
    }

    FILE *fp = fopen(BRIGHTNESS_FILE, "r+");
    if (!fp) {
        die("Failed to access brightness file");
    }

    int brightness_level = 0;
    fscanf(fp, "%d", &brightness_level);
    int new_brightness_level = 0;
    if (direction == '+' || brightness_level > 5000) {
   	new_brightness_level = brightness_level + ((direction == '+') ? MAX_BRIGHTNESS/50: -MAX_BRIGHTNESS/50);
    } else if (direction == '-') {
	new_brightness_level = brightness_level*7/10;
    }
    if (new_brightness_level == 0) {
	fclose(fp);
	die("Not writing 0 brightness");
    }

    fprintf(fp, "%d", new_brightness_level);
    fclose(fp);

    exit(EXIT_SUCCESS);
}