From 6412e6fd0f9f306b6b488191623c3ad0c6ea553c Mon Sep 17 00:00:00 2001
From: Tom Smeding <tom.smeding@gmail.com>
Date: Tue, 5 Feb 2019 13:59:25 +0100
Subject: Initial

---
 .gitignore   |  1 +
 Makefile     | 20 ++++++++++++++++
 brightness.c | 76 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 97 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 Makefile
 create mode 100644 brightness.c

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..72eb06f
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+brightness
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..8317a0b
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,20 @@
+CC = gcc
+CFLAGS = -Wall -Wextra -O2 -std=c11 -fwrapv
+INSTALL_DIR = $(HOME)/prefix/bin
+
+BIN = brightness
+
+.PHONY: all clean install
+
+all: $(BIN)
+
+clean:
+	rm -f $(BIN)
+
+install:
+	sudo install -o root brightness $(INSTALL_DIR)
+	sudo chmod +s $(INSTALL_DIR)/brightness
+
+
+$(BIN): brightness.c $(wildcard *.h)
+	$(CC) $(CFLAGS) $(filter %.c,$^) -o $@
diff --git a/brightness.c b/brightness.c
new file mode 100644
index 0000000..feee058
--- /dev/null
+++ b/brightness.c
@@ -0,0 +1,76 @@
+// By Tom Smeding (2016)
+// modified for new laptop (2017)
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdarg.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/types.h>
+
+#define INCREMENT 100
+
+__attribute__((noreturn))
+__attribute__((format (printf, 1, 2)))
+void die(const char *format,...){
+	va_list ap;
+	va_start(ap,format);
+	vprintf(format,ap);
+	va_end(ap);
+	putchar('\n');
+	exit(1);
+}
+
+int get_max_brightness(void){
+	FILE *f=fopen("/sys/class/backlight/intel_backlight/max_brightness","r");
+	if(!f)die("Could not open max_brightness file");
+	int n;
+	fscanf(f,"%d",&n);
+	fclose(f);
+	return n;
+}
+
+int get_brightness(void){
+	FILE *f=fopen("/sys/class/backlight/intel_backlight/brightness","r");
+	if(!f)die("Could not open brightness file");
+	int n;
+	fscanf(f,"%d",&n);
+	fclose(f);
+	return n;
+}
+
+void set_brightness(int n){
+	FILE *f=fopen("/sys/class/backlight/intel_backlight/brightness","w");
+	if(!f)die("Could not open brightness file");
+	fprintf(f,"%d",n);
+	fflush(f);
+	fclose(f);
+}
+
+int main(int argc,char **argv){
+	uid_t uid=geteuid();
+	if(uid!=0){
+		printf("brightness will only work with root.\n");
+		return 1;
+	}
+
+	if(argc==1){
+		printf("max: %d\n",get_max_brightness());
+		printf("current: %d\n",get_brightness());
+	} else if(argc==2){
+		int n;
+		if(strcmp(argv[1],"-")==0){
+			n=get_brightness()-INCREMENT;
+			if(n<0)n=0;
+		} else if(strcmp(argv[1],"+")==0){
+			n=get_brightness()+INCREMENT;
+			int mx=get_max_brightness();
+			if(n>mx)n=mx;
+		} else {
+			char *endp;
+			n=strtol(argv[1],&endp,10);
+			if(argv[1][0]=='\0'||*endp!='\0')die("Invalid number '%s'",argv[1]);
+		}
+		set_brightness(n);
+	}
+}
-- 
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