Function perform_assignments 

pub async fn perform_assignments(
    env: &mut Env,
    assigns: &[Assign],
    scope: Scope,
    export: bool,
    xtrace: Option<&mut XTrace>,
) -> Result<Option<ExitStatus>>

Performs assignments.

This function calls perform_assignment for each Assign. The return value is the exit status of the last command substitution performed during the expansion of the assigned values, if any

If xtrace is Some instance of XTrace, the expanded assignment words are written to its assignments buffer.