blmgr.c

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

#define BACKLIGHT_PATH_BASE "/sys/class/backlight/intel_backlight/"

void
usage()
{
    fprintf(stderr,
            "usage: blmgr\n"
            "       blmgr [+ | -]number[\%%]\n"
            );
    exit(EXIT_FAILURE);
}

int
main(int argc, char** argv)
{
    int max_brightness, current_brightness;

    FILE* max_brightness_file = fopen(BACKLIGHT_PATH_BASE "max_brightness", "r");
    if (!max_brightness_file) {
        perror("Failed to open " BACKLIGHT_PATH_BASE "max_brightness");
        return EXIT_FAILURE;
    }

    fscanf(max_brightness_file, "%d", &max_brightness);
    fclose(max_brightness_file);

    FILE* current_brightness_file = fopen(BACKLIGHT_PATH_BASE "brightness", "r");
    if (!current_brightness_file) {
        perror("Failed to open " BACKLIGHT_PATH_BASE "brightness");
        return EXIT_FAILURE;
    }

    fscanf(current_brightness_file, "%d", &current_brightness);
    fclose(current_brightness_file);

    if (argc < 2) {
        printf("%d%%\n", (int)round(((double)current_brightness / (double)max_brightness * 100.0)));
        return EXIT_SUCCESS;
    }

    static int change_mult = 1;
    static int brightness;

    switch (argv[1][0]) {
        case '-':
            change_mult = -1;
        case '+':
            {
                int brightness_change;

                if (sscanf(&argv[1][1], "%d", &brightness_change) > 0) {
                    if (strchr(&argv[1][1], '%'))  {
                        brightness_change *= ((double)max_brightness / 100.0);
                    }
                    brightness = current_brightness + brightness_change * change_mult;
                } else {
                    fprintf(stderr, "Unknown argument provided: %s\n", argv[1]);
                    usage();
                }
                break;
            }
        default:
            if (sscanf(argv[1], "%d", &brightness) > 0) {
                if (strchr(argv[1], '%')) {
                    brightness = round((double)brightness * ((double)max_brightness / 100.0));
                }
            } else {
                fprintf(stderr, "Unknown argument provided: %s\n", argv[1]);
                usage();
            }
            break;
    }

    if (brightness > max_brightness) {
        brightness = max_brightness;
    }

    printf("Setting brightness to %d\n", brightness);

    FILE* brightness_file = fopen(BACKLIGHT_PATH_BASE "brightness", "w");
    if (!brightness_file) {
        perror("Failed to open " BACKLIGHT_PATH_BASE "brightness with write access");
        return EXIT_FAILURE;
    }

    fprintf(brightness_file, "%d", brightness);

    return EXIT_SUCCESS;
}