A Simple Volume Script

Today we will be looking at 2 lines of shell script. While they may look quite unassuming, when bound to a shortcut (super-v in my case) they will give you a nice and elegant interface for changing the volume on your system. A demonstration can be found here.

The pre-requisite programs for today are the following

• pamixer
• wjt
• xargs

Without further ado here is the script.

wjt -x $(pamixer --get-volume) \
| xargs -I? pamixer --set-volume ?

The best place to start explaining this is probably wjt.

wjt is a very simple program, when you run it it gives the user a slider bar at the top of their screen. Whenever the user changes the value of the slider (by clicking or using one of the shortcuts, see man wjt) the new value is printed to stdout. An initial value can be provided though the -x flag as we do in our script.

Next we use pamixer to interface with pulseaudio. On the first line pamixer --get-volume does exactly what you would expect, it prints the current volume. Say the current volume is 20. When we run wjt -x $(pamixer --get-volume) the code inside the $() is run first. This code is then replaced by its output, which we established is 20, giving us wjt -x 20. When this is then executed a slider pops up with an initial value of 20.

Finally we will cover xargs. When the first line is executed its output (the new values of the slider) is put into the input of the second using the pipe (|) operator. xargs then takes each line of this output and runs the given command with the ? replaced with the input on that line. Say we run the whole script and then change the slider to 21, xargs will receive a line of input containing 21. It will then take its given command pamixer --set-volume ? and replace the wildcard given by the -I flag (in this case ?) with that line of input and then run the new command. This results in xargs running the command pamixer --set-volume 21 which has exactly the effect you would expect, the system volume is set to 21. xargs then repeats this process for every new line of input, giving us a simple, elegant volume widget.