bash - Get list of variables whose name matches a certain pattern

Question

In bash

echo ${!X*}

will print all the names of the variables whose name starts with 'X'.
Is it possible to get the same with an arbitrary pattern, e.g. get all the names of the variables whose name contains an 'X' in any position?

Answer 1

Use the builtin command compgen:

compgen -A variable | grep X