read-string is a built-in function in ‘C source code’. (read-string PROMPT &optional INITIAL-INPUT HISTORY DEFAULT-VALUE INHERIT-INPUT-METHOD) Read a string from the minibuffer, prompting with string PROMPT. If non-nil, second arg INITIAL-INPUT is a string to insert before reading. This argument has been superseded by DEFAULT-VALUE and should normally be nil in new code. It behaves as INITIAL-CONTENTS in ‘read-from-minibuffer’ (which see). The third arg HISTORY, if non-nil, specifies a history list and optionally the initial position in the list.