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Filename : on_ac_power
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#!/bin/sh
#
# Returns 0 (true) if on AC power
#         1 (false) if not on AC power
#         255 (false) if can't tell
#
# Example shell script:
#     if on_ac_power; then
#       echo We're on AC power
#     else
#       echo Can't say we're on AC power
#     fi

set -e

# sysfs
#
# This algorithm is complicated by the possibility of multiple AC
# adapters.  We scan the ac_adapter/power_supply directory looking for adapters
# that have known states.  If any adapter is on-line, we return 0.  If
# no adapters are on-line but one or more are off-line, we return 1.
#
OFF_LINE_P=no

if [ -d /sys/class/power_supply/ ]; then
    for FN in /sys/class/power_supply/*; do
	if test -d "${FN}" && test -r "${FN}/type"; then
	    type="$(cat "${FN}/type")"
	    case "${type}" in
	    Mains|USB*|BrickID|Wireless)
		if [ -r "${FN}/online" ]; then
		    online="$(cat "${FN}/online")"
		    [ "$online" = 1 ] && exit 0
		    [ "$online" = 0 ] && OFF_LINE_P=yes
		fi;;
	    esac
	fi
    done
    [ "${OFF_LINE_P}" = "yes" ] && exit 1
fi

# ACPI
# same algorithm as above, a fallback only when the generic sysfs interface
# is not available (old kernels only)
if [ -d /proc/acpi/ac_adapter ]; then
    for FN in /proc/acpi/ac_adapter/*; do
	if [ -d "${FN}" ]; then
	    if [ -r "${FN}/state" ]; then
		grep --quiet on-line "${FN}/state" && exit 0
		grep --quiet off-line "${FN}/state" && OFF_LINE_P=yes
	    elif [ -r "${FN}/status" ]; then
		grep --quiet on-line "${FN}/status" && exit 0
		grep --quiet off-line "${FN}/status" && OFF_LINE_P=yes
	    fi
	fi
    done
    [ "${OFF_LINE_P}" = "yes" ] && exit 1
fi

# PMU
if [ -r /proc/pmu/info ]; then
    exec awk </proc/pmu/info '
	BEGIN { FS=":"; ret = 255 }
	/^AC Power.*1$/ { ret = 0; exit }
	/^AC Power.*0$/ { ac = 1 }
        /^Battery.*/ {
                if ($2 ~/0/ && ac == 1)
                        ret = 0
                else
                        ret = 1
                exit }
	END { exit ret }
    '
fi

# APM
if [ -r /proc/apm ]; then
    exec awk </proc/apm '
	BEGIN { ret = 255 }
	/^[0-9.a-zA-Z]* [0-9.]* 0x.. 0x../ {
		if ($4 == "0x01") { ret = 0; exit }
		else if ($4 == "0x00") { ret = 1; exit }
	}
	END { exit ret }
    '
fi

# nothing is available
exit 255