Бармар был близок, но без сигар: -)
find . -maxdepth 1 -type f -iname 'x[0-9]'
Со следующим пояснением:
. is the current directory (~ is the home directory of the current user)
-maxdepth 1 means: find within that directory (don't look into subdirectories)
-iname 'x[0-9]' means: the name must be like "x" (case insensitive), followed by a number 0..9