Bash script for power AC plugin

Question

I'm working on a bash script that runs in an infinite 1 second loop, where if it detects that the computer is plugged into AC power, it plays the file plugin.ogg with ogg123, and if it is not plugged in, it plays a silent file Silence.ogg. However, I have a few issues. First, it seems to no longer loop (probably a side effect of the wait I had to throw in in order to avoid a looping charger input sound after the first detection. Secondly, it doesn't seem to want to change to the / directory and it therefore (I'm not sure if due to the / error or something else) can't find the files to play. Please help fix this, thanks!

#!/bin/bash
"cd /"

while true
do
    if on_ac_power; then 
        "ogg123 plugin.ogg"               ## Laptop on power
    else
        "ogg123 Silence.ogg"          ## Laptop on battery
    fi
    sleep 10                       ## wait 10 sec before repeating
done

Terminal output if run while computer is unplugged: /home/brenden_mcfarling_live/Desktop/ac0.sh: line 3: cd /: No such file or directory

/home/brenden_mcfarling_live/Desktop/ac0.sh: line 10: ogg123 Silence.ogg: command not found

Terminal output when run while plugged in: /home/brenden_mcfarling_live/Desktop/ac0.sh: line 3: cd /: No such file or directory

/home/brenden_mcfarling_live/Desktop/ac0.sh: line 8: ogg123 plugin.ogg: command not found

Any help would be appreciated!

Answer 1

At first: Why are you changing directory to root / ? Are your files located there ?

Remove the qoutes ".." from your command. So that it looks like

ogg123 plugin.ogg

Make sure that you have installed the package vorbis-tools

# sudo apt-get install vorbis-tools

Answer 2

As @JonnyTischbein said: remove the quotes from your commands because else the shell will try to execute the literal command "cd /", i.e. it will search for an executable file called "cd /" and execute it. Of course, it does not exist and you get bash: cd /: No such file or directory.

The same goes for "ogg123 plugin.ogg". It will try to execute the file "ogg123 plugin.ogg" which also doesn't exist. Given your other error messages I assume that the *.ogg files reside in /home/brenden_mcfarling_live/Desktop (and not in /). Thus, after changing to / the files cannot be found any more and you need to supply the full path.

Put together:

#!/bin/bash
cd /

while true
do
    if on_ac_power; then 
        ## Laptop on power
        ogg123 /home/brenden_mcfarling_live/Desktop/plugin.ogg
    else
        ## Laptop on battery
        ogg123 /home/brenden_mcfarling_live/Desktop/Silence.ogg
    fi
    ## wait 10 sec before repeating
    sleep 10
done

If the path-to or filename-of the sound files contained spaces, then you can use quotes but only around the filename:

ogg123 "/home/brenden_mcfarling_live/Desk Top/Very silent sound.ogg"

---

You may also want to have a look at this question (and its answer) at Unix & Linux. There they say how to immediately catch the event of plugging/unplugging the AC adapter so you don't need to poll every 10 seconds but get triggered instead.

I admit, it's a bit complicated at first sight but the idea is:

• Do an educated guess what events happen when the cord is plugged in and out
• Write a script that gets called for "plugged in" (that plays your first sound file)
• Write a script that gets called for "plugged out" (that plays your second sound file)
• Create two rules in a new file below /etc/udev/rules.d that say "when plugged in, then run script1.sh" and "when unplugged, then run script2.sh"