So, I asked myself, why not try and find a way to dynamically update my login screen with battery information? There are a number of posts for updating the login text. I took this basic idea and combined it with a Python script I wrote for parsing out the battery status.
Some of the content in the battery script was taken from a recent post on Lifehacker, showing how you can build a script which will vocally alert you when your battery status is getting critical.
Anyway, the first step was to build a script (I prefer Python) which will gather battery stats from ioreg and parse it for the current battery capacity, maximum battery capacity, and external charge capability. The last option (yes/no) lets us know if the laptop is plugged into the wall.
Here's the script I came up with
#!/usr/bin/python
import subprocess
import os, sys
BATTERY_CMD = ["/usr/sbin/ioreg", "-l"]
GREP_CMD = ["/usr/bin/egrep", "Capacity|ExternalChargeCapable"]
def main(argv):
content = getBatteryStatus()
print(content)
return 0
def getBatteryStatus():
process = subprocess.Popen(BATTERY_CMD, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
grep = subprocess.Popen(GREP_CMD, stdin=process.stdout, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
grep.wait()
output = grep.communicate()[0]
batteryStatus = output.split("\n")
if len(batteryStatus) < 3:
print(batteryStatus)
return "Could not get battery status"
if "Yes" in batteryStatus[0]:
return "Laptop is plugged into the wall"
else:
maxCapacity = float(batteryStatus[1].split("=")[1].lstrip())
curCapacity = float(batteryStatus[2].split("=")[1].lstrip())
remaining = 100 * (curCapacity / maxCapacity)
return "Battery Remaining: %.02f%s" % (remaining, "%")
if __name__ == "__main__":
sys.exit(main(sys.argv))This script basically runs the following command: ioreg -l | egrep Capacity|ExternalChargeCapable. This bundles the content into a large string, delimited by "\n" characters. Parsing this is a simple value of extracting everything after the "=" sign.
Anyway, this script prints either the percentage or the status of the wall plug.
The second part of this exercise was to create a StartupItem for my Macbook. This was actually very easy (as the upper link shows). Create a new directory in "/Library/StartupItems" called logintext. Inside this directory, you'll need to copy the above script, and add 2 new scripts:
Call the first one, StartupParameters.plist, and add the following content:
{
Description = "Sets LoginwindowText";
Provides = ("logintext");
}This script informs the startup process of which script to execute when starting up. This guarantees all initializations of the Macbook will have up-to-date knowledge of the battery life.
The last script is called "logintext". In this script, put the following content:
#!/bin/sh
batteryText=`/Library/StartupItems/logintext/batteryScript.py`
defaults write /Library/Preferences/com.apple.loginwindow LoginwindowText "$batteryText"
This script executes the Python script and sets the loginwindow's preference (LoginwindowText) to the output from the script.
Log in as root (
sudo su -) and add a new cronjob to execute this script every 2 minutes:
*/2 * * * * /Library/StartupItems/logintext/logintext
And it should keep your system relatively up-to-date!
