Get list of variables whose name matches a certain pattern

Use the builtin command compgen:

compgen -A variable | grep X

Easiest might be to do a

printenv |grep D.*=

The only difference is it also prints out the variable's values.

This should do it:

env | grep ".*X.*"

Edit: sorry, that looks for X in the value too. This version only looks for X in the var name

env | awk -F "=" '{print $1}' | grep ".*X.*"

As Paul points out in the comments, if you're looking for local variables too, env needs to be replaced with set:

set | awk -F "=" '{print $1}' | grep ".*X.*"