Bash: Reading in a string from a file with variable substitution

I have a weird situation where I have a command stored in a file and that file contains references to variables.

I'm able to read the file just fine, but I'm having trouble getting variable expansion working.

As a minimum working example, here is a file that contains a command with a variable as an example:

command.in

ls $DIR

simple.sh

#!/bin/bash

MYVAR=$(<command.in)
DIR="/tmp"

$MYVAR

Expected Results

My expected results is that it'll print the contents of /tmp

What I've tried

I've tried moving DIR assignment above MYVAR assignment in simple.sh and I've tried changing the $DIR in command.in to ${DIR} and $(DIR)

$(<command.in) does dereference a variable. You can see what is happening if you put an echo in the script:

#!/bin/bash
DIR="/tmp"
MYVAR=$(<command.in)
echo $MYVAR
$MYVAR

which gives:

bash simple.sh
ls $DIR
ls: cannot access '$DIR': No such file or directory

When you do $MYVAR, the variable gets expanded, once. So it produces ls $DIR and that is what is executed. With eval you can force another level of variable expansion:

#!/bin/bash
DIR="/tmp"
MYVAR=$(<command.in)
echo "$MYVAR"
eval "$MYVAR"