Requirements

To use the readline functions, you need to install libreadline. You can find libreadline on the home page of the GNU Readline project, at » https://tiswww.case.edu/php/chet/readline/rltop.html. It's maintained by Chet Ramey, who's also the author of Bash.

You can also use these functions with the libedit library, a non-GPL replacement for the readline library. The libedit library is BSD licensed and available for download from » http://www.thrysoee.dk/editline/.

The two libraries do not provide the same features, so some functions are absent from some builds. The functions driving the callback interface, readline_callback_handler_install(), readline_callback_handler_remove(), readline_callback_read_char(), readline_redisplay() and readline_on_new_line(), are only present when the underlying library provides them, and are absent on Windows. Calling an absent function throws an Error. function_exists() tests for a given function, and the READLINE_LIB constant reports which library is in use.