Simple generic monitoring tool using a finite-state-machines implementation.

monitor.sh

#!/bin/bash
#
# Simple monitoring using a finite state machines 
set -e -u -o pipefail

# Print debug output to standard error
debug() {
  echo "[${FUNCNAME[1]}] $@" >&2
}

# Say a phrase using the soundarc
say() {
  debug "$@"
  espeak "$@" 2>/dev/null
}

# Return percentage level of a the battery (BAT0) of laptop
get_battery_percentage() {
  local CHARGE_NOW=$(</sys/class/power_supply/BAT0/charge_now)
  local CHARGE_FULL=$(</sys/class/power_supply/BAT0/charge_full)
  local PERCENTAGE0=$(($CHARGE_NOW * 100 / $CHARGE_FULL))
  echo $(($PERCENTAGE0 > 100 ? 100 : $PERCENTAGE0))
}

### Services

# battery_status: Sound notifications of change of state for the BAT0 battery
battery_status_INITIAL_STATE="Full"
battery_status() {
  local OLD_STATUS=$1
  local STATUS=$(</sys/class/power_supply/BAT0/status)
  
  debug "STATUS=$STATUS"
  if test "$STATUS" != "$OLD_STATUS" &&
     test "$STATUS" != "Full" -o "$OLD_STATUS" != "Charging"; then
    say "$STATUS"
  fi
  echo $STATUS
}

# battery_status: Suspend the computer when the battery level is too low.
battery_level_INITIAL_STATE="0"
battery_level() {
  local STATE=$1
  local ABSOLUTE_MINIMUM=5
  local THRESHOLD=50
  local PERCENTAGE=$(get_battery_percentage)
  local STATUS=$(</sys/class/power_supply/BAT0/status)
  
  debug "PERCENTAGE=$PERCENTAGE"
  if test $PERCENTAGE -lt $ABSOLUTE_MINIMUM ||
     test "$STATUS" = "Discharging" -a $PERCENTAGE -lt $THRESHOLD; then
    say "Battery at $PERCENTAGE%, suspending"
    sudo pm-suspend
  fi
  echo $PERCENTAGE
}

### Monitoring infrastructure

monitor() {
  local LOOP_WAIT=$1
  shift

  # Declare state variables (${FUN}_STATE)
  for FUN in $*; do
    debug "Init service: $FUN"
    eval "local ${FUN}_STATE=\$${FUN}_INITIAL_STATE"
  done

  while true; do
    for FUN in $*; do
      local STATE_VAR="${FUN}_STATE"
      local STATE=${!STATE_VAR}
      local NEW_STATE=$($FUN "$STATE")
      eval "${STATE_VAR}=\$NEW_STATE"
      sleep $LOOP_WAIT
    done
  done
}

### Main

monitor 1 "battery_status" "battery_level"