The following script shows the actual value of “$()” and “${}” first, and then put all “$()” and “${}” inside a variable “x” as a string contains some bash expressions inside, finally, try to use “$(eval)” to convert all “$()” and “${}” into actual value, and then set the result to “y“.

# echo "id: $(id)"
id: uid=0(root) gid=0(root) groups=0(root)

# echo "whoami: $(whoami)"
whoami: root

# x='hello world: "$(id)", whoami: "$(whoami)"'
# echo "x: $x"
x: hello world: "$(id)", whoami: "$(whoami)"

y="$(eval "$x")"
echo "y: $y"

I expect the $(eval) can evaluate any given string and auto parse all $() and ${} inside that string, but got the following error when executing the y="$(eval "$x")":

Command 'hello' not found, but can be installed with:
apt install hello

Here is the expected output:

y: hello world: uid=0(root) gid=0(root) groups=0(root), whoami: root

How to replace all “$()” and “${}” inside a bash variable “x“?