Function expand_variables 

pub fn expand_variables(
    input: &str,
    args: &HashMap<String, String>,
    env: &HashMap<String, String>,
) -> String

Expand variables in a string using the provided ARG and ENV maps.

Variables are expanded in the following order of precedence:

1. Build-time ARGs (provided at build time)
2. ENV variables (from Dockerfile ENV instructions)
3. Default ARG values (from Dockerfile ARG instructions)

Arguments

• input - The string containing variable references
• args - ARG variable values (build-time and defaults)
• env - ENV variable values

Returns

The string with all variables expanded