Environment:
Linux Mint, Cinnamon desktop manager, with multiple workspaces=virtual desktops, e.g. 4.
Bash script
What is known:
How to determine the number of workspaces:
wmctrl -d | wc -l
What I need:
Get the number of virtual desktops the bash script is running on with a pure bash as var (like with grep, not awk or similar) and echo the var.
You can use POSIX shell features and the xprop(1) command to get both details with no other external utilities.
To get the ID number of the current/active desktop:
curdesk=$(xprop -root -notype _NET_CURRENT_DESKTOP)
curdesk="${curdesk##* }"
To get the count/quantity of desktops defined:
deskcnt=$(xprop -root -notype _NET_NUMBER_OF_DESKTOPS)
deskcnt="${deskcnt##* }"
Both depend on xprop(1) giving the answer in the form "foo = 0" (separated by spaces), and use shell pattern matching parameter expansion to match the longest substring ending in space, and remove it, leaving only the last token (the value after the equals sign).
Note that desktops are numbered from 0 (zero), so the count will be a number one higher than the ID number of the last desktop.
This should work with any window manager that adheres to the Extended Window Manager Hints (EWMH) specification (which is practically all of them, these days):
https://specifications.freedesktop.org/wm-spec/1.3/ar01s03.html