Initialize

.gitignore

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+backlight-control

Makefile

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+CFLAGS=-Wall -Wextra -Werror -std=c99 -pedantic -O2
+
+backlight-control: main.c
+	$(CC) $(CFLAGS) -o $@ $^ $(LDFLAGS)

README.md

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+A basic tool to increase and decrease intel backlight percent.
+
+## Build
+
+You'll need `make` and some C compiler installed.
+
+```
+make
+```
+
+That's it.
+
+## Usage
+
+Copy the `backlight-control` file to `/usr/local/bin/` or somewhere similar.
+Then run `backlight-control` to get the current brightness as a percentage, or
+`backlight-control +1` to increase brightness by 1 percent, or
+`backlight-control -1` to decrease brightness by 1 percent. Or higher numbers
+for higher percentages at a time.

main.c

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+#include <stdio.h>
+#include <stdlib.h>
+
+void print_usage(char *argv[])
+{
+  fprintf(stderr, "Usage: %s <value>\n"
+                  "\n"
+                  "value:\n"
+                  "\t +percent - increase brightness by percent\n"
+                  "\t -percent - decrease brightness by percent\n",
+          argv[0]);
+}
+
+int read_file(const char *path)
+{
+  FILE *file = fopen(path, "r");
+  int value;
+  int read = fscanf(file, "%d", &value);
+  fclose(file);
+  if (read != 1)
+  {
+    printf("Error reading %s\n", path);
+    exit(1);
+  }
+  return value;
+}
+
+int max_brightness()
+{
+  return read_file("/sys/class/backlight/intel_backlight/max_brightness");
+}
+
+int brightness()
+{
+  return read_file("/sys/class/backlight/intel_backlight/brightness");
+}
+
+int brightness_percent()
+{
+  return (brightness() * 100) / max_brightness();
+}
+
+int main(int argc, char *argv[])
+{
+  if (argc < 2)
+  {
+    printf("%d\n", brightness_percent());
+    return 0;
+  }
+
+  if (argc > 3)
+  {
+    print_usage(argv);
+    exit(2);
+  }
+
+  int positive = 0;
+  if (argv[1][0] == '-')
+  {
+    positive = 0;
+  }
+  else if (argv[1][0] == '+')
+  {
+    positive = 1;
+  }
+  else
+  {
+    print_usage(argv);
+    exit(2);
+  }
+
+  int percent;
+  char *number_str = argv[1] + 1;
+  int read = sscanf(number_str, "%d", &percent);
+  if (read != 1)
+  {
+    print_usage(argv);
+    exit(3);
+  }
+
+  int current = brightness();
+  int max = max_brightness();
+  int change = (max * percent) / 100 * (positive ? 1 : -1);
+  FILE *file = fopen("/sys/class/backlight/intel_backlight/brightness", "w");
+
+  int set_to = current + change;
+  // clamp
+  if (set_to > max)
+  {
+    set_to = max;
+  }
+  if (set_to < 0)
+  {
+    set_to = 1;
+  }
+  fprintf(file, "%d", set_to);
+}