2009-12-14
Ah, the age old question "how does one display laptop battery information at the bottom of a screen terminal?"

Well finally, there is an answer. Actually, there are probably quite a few different answers, but this one is my answer. Since I wanted to replicate some of the functionality of my other battery monitor (vattery), this battery monitor can perform commands when the battery level drops to a certain percent. By the way, this requires that acpi is installed and running.

Let's start with the code to read and process the battery info.
#!/bin/sh #we need a function to run when the battery gets low low_battery_action () {     echo "the battery is getting low" } #what files have our needed data?    state_file="/proc/acpi/battery/BAT0/state" info_file="/proc/acpi/battery/BAT0/info" #by default, the action has not been performed action_performed=0 #at what percent does the action get run? action_percent=10 # start the loop while ]; do     #get info about the battery     battery_current_charge=`cat $state_file | grep remaining | awk '{print $3}'`     battery_ac_state=`cat $state_file | grep charging | awk '{print $3}'`     battery_last_total_charge=`cat $info_file | grep last | awk '{print $4}'`     battery_percent=$((100*battery_current_charge/battery_last_total_charge))     #display the info     echo "battery: $battery_percent% $battery_ac_state"     if $action_performed -eq # has the low power action been performed?     then    # if "yes"         if $battery_ac_state "charging" # is the battery charging?         then #if "yes"             #is the battery percent greater than the action percent?             if $battery_percent -gt $action_percent ]             then                 #reset the action_performed to false                 action_performed=0             fi         fi     else #the low power action has not been performed         #is the battery percent less than or equal to the action percent?         if $battery_percent -le $action_percent ]         then              #perform the action             low_battery_action             #set the action_performed to true             action_performed=1         fi     fi     # take a two second nap     sleep 2 done
I have this saved as battery_state.sh in my ~/bin directory, which is in my $PATH. If ~/bin isn't part of your $PATH, don't worry, you can just make a directory called "scripts" and put the file in the "scripts" directory. The file should be set to executable by issuing
chmod +x ~/bin/battery_state.sh
Adjust the command accordingly if your file is not in the ~/bin directory.

Since the code doesn't do anything major when the battery charge drops to 10 percent, change line 5 to whatever command or commands you wish to occur. I'm a big fan of
espeak -g7 -ven-us+f3 "Hello? is anyone there? my battery power is low. please plug in my charger."
To adjust when the command is run, edit line 13 and set the action_percent to the percent of charge that the battery needs to reach for the command to run.

Now it is time to setup screen to run the battery_state.sh script and process the scripts output when screen is run. To do this, the ~/.screenrc file needs to be edited (if the file doesn't exist, just create the file).

The following should be added to the .screenrc file
hardstatus alwayslastline backtick 1 0 0 battery_state.sh hardstatus string '%1`'
Now start screen.
If the battery_state.sh file is not in a directory that is part of your $PATH, adjust the backtick 1 0 0 battery_state.sh line to be backtick 1 0 0 /path/to/your/battery_state.sh using the actual path to your battery_state.sh file.

Now quit reading, and go write something.
Comments
2010-03-21 jamie trenchard:
Works perfectly for me. (Except I had to change the path to my battery, but hey, at least it's not like the net going down)
Now I don't have to worry about my laptop suddenly running out of battery.
2010-03-21 jezra:
Quite a few distros these days are starting to count batteries beginning with 1 instead of 0. So instead of information being in "/proc/acpi/battery/BAT0" it might be in "/proc/acpi/battery/BAT1". Similarly, this code doesn't handle multiple batteries.
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