My system is really limited and lacking what some would consider dealbreaking features. Linux is a fine sturdy OS, but by default some of the functionality can feel a bit too basic. Like the battery charge monitoring, wouldn't it be nice to see a clean percentage, rather than a huge charge value?
Thankfully linux gives us some text based IO, (sysfs, /sys), that can be dealt with using standard posix shell scripts. So I decided to write some scripts to improve my current situation with no good battery meter, or backlight power control.

Below are some quick examples of how to interact with /sys to control linux hardware. Linux sysfs contains an abundance of data about the hardware, also you can change certain variables, like the backlight script you will at the end of this article.

Here's an easy one, some gpu and display related files, in addition to what you can already find in /dev/dri.

gpu_displays.sh:

#!/bin/sh
find /sys/class/drm 

Ok that was weak, here is something actually useful. let's use our friend bc to print out the current battery charge as a percentage. We previously learned about how to use bc, a powerful math command. see the shell_math article for more info.

battery_charge.sh:

#!/bin/sh
#
# FIXME: missing support for multiple batteries
#

if [ ! -e "/sys/class/power_supply" ]; then 
   echo "/sys/class/power_supply not found, is sysfs mounted?" 
   exit -1 
fi 

#PLUGGED_IN=$(cat /sys/class/power_supply/AC/online)
CHARGE_FULL=$(cat /sys/class/power_supply/BAT0/charge_full) 
CHARGE_NOW=$(cat /sys/class/power_supply/BAT0/charge_now) 
CHARGE_STATUS=$(cat /sys/class/power_supply/BAT0/status) 
CHARGE_PERCENT=$(echo "scale=5; $CHARGE_NOW / $CHARGE_FULL * 100" | bc | sed -E -n "s/(..\....).*/\1/p") 

echo "$CHARGE_STATUS: $CHARGE_PERCENT%" 

This last script will let us set backlight value instead of wasting energy at maximum. backlight_power.sh:

#!/bin/sh
#
# FIXME: only tested on intel_backlight driver,
# it may or may not work with multiple backlights/displays
#

if [ ! -e "/sys/class/backlight" ]; then 
   echo "/sys/class/backlight not found, is sysfs mounted?" 
   exit -1 
fi 

print_usage() { 
   echo "" 
   echo " print or set the power of backlight" 
   echo "" 
   echo "backlight_power usage:" 
   echo "   backlight_power           -- print current power by percent" 
   echo "   backlight_power <percent> -- set backlight by percent" 
   echo "" 
   echo "" 
   exit -1 
} 

if [ "$1" = "" ]; then 
   SET_POWER=0 
else 
   CHECK_PERCENT=$(echo $1 | sed "s/[0-9]//g") 
   if [ "$CHECK_PERCENT" != "" ]; then 
      echo "expected an integer (0 .. 100) percentage" 
          print_usage 
   fi 
   if [ $1 -gt 100 ]; then 
      SET_POWER=100 
   elif [ $1 -le 0 ]; then 
      SET_POWER=1 
   else 
      SET_POWER=$1 
   fi 
fi 

BACKLIGHTS=$(find /sys/class/backlight -mindepth 1 -maxdepth 1) 

IFS=$'\n' 
for BACKLIGHT in $BACKLIGHTS; do 
   POWER_MAX=$(cat $BACKLIGHT/max_brightness) 
   POWER_NOW=$(cat $BACKLIGHT/brightness) 
   if [ "$SET_POWER" = "0" ]; then 
      POWER=$(echo "scale=5; $POWER_NOW / $POWER_MAX * 100" | bc | sed -E -n "s/(..\....).*/\1/p") 
      echo "$BACKLIGHT: $POWER%" 
   else 
      POWER=$(echo "scale=5; $POWER_MAX * $SET_POWER / 100" | bc | sed -E -n "s/(.*)\..*/\1/p") 
      echo "setting $BACKLIGHT/brightness to: $POWER, $SET_POWER% " 
      printf "$POWER" > $BACKLIGHT/brightness 
      printf "($POWER) > $BACKLIGHT/brightness" 
   fi 
done