Dim the screen with xbacklight using 1, 2, 3 buttons.

dim.sh

#!/bin/bash -

# Dim the screen with xbacklight using 1, 2, 3 buttons.

dim()
{
    local prog=/usr/bin/xbacklight
    local step=20 state

    which $prog >/dev/null
    case $? in
      1)  echo $prog is not installed
          return 1
    esac

    while true
    do
      state=$($prog -get)
      echo -n "${state%%.*}%% "

      read -sn1
      case $REPLY in
        1|[Ww])  $prog -inc $step ;;
        2|[Ss])  $prog -dec $step ;;
        3|[Xx])  echo; break ;;
             *)  continue ;;
      esac

      state=$($prog -get)
      if ((${state%%.*}==100)) || ((${state%%.*}==0)); then
        echo ${state%%.*}%%
        return 1
      fi
    done
}

dim