Wei Wu / @lazyparser

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(针对Debian/Ubuntu发行版)

以下的代码可以判断电脑是否电池供电(来自于/etc/cron.daily/mlocate,apt 也使用了类似的脚本):

if which on_ac_power >/dev/null 2>&1; then ON_BATTERY=0 on_ac_power >/dev/null 2>&1 || ON_BATTERY=$? if [ “$ON_BATTERY” -eq 1 ]; then exit 0 fi fi

这段脚本使用“on_ac_power”这个小工具来判断是否AC电源供电。这个工具属于包“powermgmt-base”,默认安装。“on_ac_power”没有参数,启动后没有屏幕输出,通过返回值来发挥结果:

这个工具位于“/sbin/”目录下,同时在“/usr/bin/”目录下有一个符号链接指向前者。也是一个 Bash 脚本,不到一百行代码,通过“/proc/”目录中的信息来进行判断。

#!/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 ${FN}/type)” if test “x${type}” = “xMains”; then if [ -r “${FN}/online” ]; then online=”$(cat ${FN}/online)” [ “$online” = 1 ] && exit 0 [ “$online” = 0 ] && OFF_LINE_P=yes fi fi fi done [ “${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 /sbin/acpi_available && [ -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 ] && /sbin/apm_available; 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