battery_shutdown.sh

#!/bin/sh

##########################################################################
#   Description
#       Auto-shutdown on low battery.
#
#   History
#   Date        Who         Change
#   Dec 2010    J Bacon     Derived from script by DutchDaemon
##########################################################################

# Battery level critical %
critical_time=5
warning_time=15

# Time between warning user and initiating shutdown
shutdown_delay=60

# seconds to pause between script runs
battery_check_interval=60

set -x
while true; do
    ac_power=$( /sbin/sysctl -n hw.acpi.acline )
    
    if [ $ac_power = 0 ]; then
        battery_time=$( /sbin/sysctl -n hw.acpi.battery.time )
        if [ $battery_time -ge 0 ]; then
	    if [ $battery_time -le $critical_time ]; then
	        printf "Battery level is critical.\nInsert power plug within $shutdown_delay seconds to avoid shutdown.\n" | wall
	    
	        # Give user time to plug in
	        /bin/sleep $shutdown_delay
	    
	        # Recheck for external power before shutting down
	        ac_power=$( /sbin/sysctl -n hw.acpi.acline )
	        if [ $ac_power = 0 ]
		    then /sbin/shutdown -p +1
	        fi
	    fi
        elif [ $battery_time -le $warning_time ]; then
	    printf "Warning: Battery is at $battery_time minutes.\n" | wall
        fi
    fi
    /bin/sleep $battery_check_interval
done