Linux shell script implementation of `acpi -b`

battery.sh

#!/bin/sh
# Show battery information similar to `acpi -b`
if [ -n "${*:-$BAT}" ]; then for BAT in "${@:-$BAT}"; do echo "$BAT"; done
else find /sys/class/power_supply/ -maxdepth 1 -name 'BAT*' | LC_ALL=C sort
fi | while IFS= read -r BAT; do
    if [ ! -r "$BAT" ] || [ ! -r "$BAT/uevent" ]; then
        printf '%s unreadable\n' "$BAT" >&2
        continue
    fi

    sed 's/^POWER_SUPPLY_\([^=]*\)=\(.*\)$/\1="\2"/' "$BAT/uevent" >/tmp/$$.bat
    . /tmp/$$.bat
    rm -f /tmp/$$.bat

    for SUFFIX in STATUS POWER_NOW ENERGY_NOW ENERGY_FULL; do
        if [ -z "$(eval printf '%s' '$'$SUFFIX)" ]; then
            if [ "$SUFFIX" = "ENERGY_FULL" ]; then # Dead battery
                ENERGY_NOW="0"
                ENERGY_FULL="1"
                continue
            fi
            printf '%s\n' "POWER_SUPPLY_$SUFFIX not found in $BAT/uevent"
        fi
    done >&2

    case "$STATUS" in
        "Charging") ENERGY="$((ENERGY_FULL - ENERGY_NOW))" ;;
        "Discharging"|"Not charging") ENERGY="$ENERGY_NOW" ;;
        *) ;;
    esac

    printf '%s %s' "${BAT##*/}" "$STATUS"
    printf ' %d%%' "$((100 * ENERGY_NOW / ENERGY_FULL))"
    if [ -n "$ENERGY" ] && [ "$POWER_NOW" -gt "0" ]; then
        REMAINING="$((3600 * ENERGY / POWER_NOW))"
        SECS="$((REMAINING % 60))"
        MINS="$(((REMAINING / 60) % 60))"
        HOURS="$((REMAINING / 3600))"
        printf ' %02d:%02d:%02d' "$HOURS" "$MINS" "$SECS"
        [ "$STATUS" = "Charging" ] \
            && printf ' until charged' \
            || printf ' remaining'
    fi
    printf '\n'
done