Check if we on ac power or not.

on_ac_power.sh

#!/bin/sh
#
# Test if the computer is running on line power
# Exit status:
# - 0 (true)  System is on AC power
# - 1 (false) System is not on AC power
#
# NOTE: Batteries are not good indicators unless we also check their type,
#       as some peripherals have batteries.
#
# Copyright 2006 Red Hat, Inc.
# Copyright 2006 Richard Hughes
#
# Based on work from:
#    Richard Hughes <[email protected]>
#    Peter Jones <[email protected]>
#    Stefan Seyfried <[email protected]>
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of version 2 of the GNU General Public License as
# published by the Free Software Foundation.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
#

# If we do not have any power supplies, assume we are on AC
ret=0

# Iterate through power supplies sysfs knows about.  
for ps in /sys/class/power_supply/*; do
    [ -r "$ps/online" ] || continue
    # OK, we know we have an AC adaptor. 
    # Our default return changes to failed.
    ret=1
    read -r ps_status < "$ps/online"
    [ 1 -eq "$ps_status" ] && exit 0
done

exit "$ret"