Why am I getting this 'bad substitution' error in my bash command?

Question

when I run this I get this 'bad substitution' error. What can I do?

$ x="Hello World"
$ echo "$x"
Hello World
$ echo "${x^^}"
-bash: ${x^^}: bad substitution

EDIT: I would like to have it in all upper case.

Answer 1

Your method only works in bash 4. Try this:

echo $x | tr '[a-z]' '[A-Z]'