Xfce4-generic-slider is a tool to help Xfce users deal with a variable which they wish to both GET and SET. The getting side is similar to what xfce4-genmon-plugin does except the command's numerical output is represented visually in a slider. Dragging the slider is then used to set the value through calls to a second command.
Development of this plugin currently takes place at the Xfce Gitlab site. This is where any bugs you find should be reported. Also, patches (especially translations) are most welcome!
To clone the source tree and build the package, you need the Xfce development libraries.
% git clone https://gitlab.xfce.org/panel-plugins/xfce4-generic-slider.git
% cd xfce4-generic-slider
% ./autogen.sh
% make
% make install
Be sure to specify an installation prefix / DESTDIR so that it goes to the right place.
Once xfce4-generic-slider is running in your panel, you can change the color of the slider and set whether a label appears beside it. To actually use it, you need to setup three references to the variable you're interested in. Here's an example of how to make a slider for the volume.
Adjust this command: amixer set PCM %v
Denominator for adjusting: 255
Synchronize with this command: amixer get PCM | tail -1 | awk '{print $4}'
Denominator for synchronizing: 255
Label for slider: PCM: %v
Denominator for label: 255
When the slider is dragged to a certain fraction, this fraction times 255 will be passed to amixer set. When another application changes the volume, the slider will call amixer get to determine what the returned number is as a fraction of 255. Note that the right denominator can differ depending on the sound card.