Indirect variable expansion¶

${!varname} tells bash to:

1. Get the value of 'varname'
2. Use that value as the name of another variable to expand

Example:

prefix="OPENAI_PROXY"
var="${prefix}_PORT"
echo "${!var}"  # Prints the value of OPENAI_PROXY_PORT

This feature requires Bash 2.0 or later It won't work in standard sh or other shells