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AnyEvent::ReadLine::Gnu - event-based interface to Term::ReadLine::Gnu


 use AnyEvent::ReadLine::Gnu;

 # works always, prints message to stdout
 AnyEvent::ReadLine::Gnu->print ("message\n");

 # now initialise readline
 my $rl = new AnyEvent::ReadLine::Gnu prompt => "hi> ", on_line => sub {
    # called for each line entered by the user
    AnyEvent::ReadLine::Gnu->print ("you entered: $_[0]\n");

 # asynchronously print something
 my $t = AE::timer 1, 1, sub {
    print "async message 1\n"; # mind the \n

    # the same, but shorter:
    $rl->print ("async message 2\n");

 # do other eventy stuff...


The Term::ReadLine module family is bizarre (and you are encouraged not to look at its sources unless you want to go blind). It does support event-based operations, somehow, but it's hard to figure out.

It also has some utility functions for printing messages asynchronously, something that, again, isn't obvious how to do.

This module has figured it all out for you, once and for all.

$rl = new AnyEvent::ReadLine::Gnu key => value...

Creates a new AnyEvent::ReadLine object.

Actually, it only configures readline and provides a convenient way to call the show and hide methods, as well as readline methods - this is a singleton.

The returned object is the standard Term::ReadLine::Gnu object, all methods that are documented (or working) for that module should work on this object.

Once initialised, this module will also restore the terminal settings on a normal program exit.

The callback will be installed with the CallbackHandlerInstall, which means it handles history expansion and history, among other things.

The following key-value pairs are supported:

on_line => $cb->($string)

The only mandatory parameter - passes the callback that will receive lines that are completed by the user.

The string will be in locale-encoding (a multibyte character string). For example, in an utf-8 using locale it will be utf-8. There is no portable way known to the author to convert this into e.g. a unicode string.

prompt => $string

The prompt string to use, defaults to >.

name => $string

The readline application name, defaults to $0.

in => $glob

The input filehandle (should be a glob): defaults to *STDIN.

out => $glob

The output filehandle (should be a glob): defaults to *STDOUT.


These methods hide the readline prompt and text. Basically, it removes the readline feedback from your terminal.

It is safe to call even when AnyEvent::ReadLine::Gnu has not yet been initialised.

This is immensely useful in an event-based program when you want to output some stuff to the terminal without disturbing the prompt - just hide readline, output your thing, then show it again.

Since user input will not be processed while readline is hidden, you should call show as soon as possible.


Undos any hiding. Every call to hide has to be followed to a call to show. The last call will redisplay the readline prompt, current input line and cursor position. Keys entered while the prompt was hidden will be processed again.

$rl->print ($string, ...)
AnyEvent::ReadLine::Gnu->print ($string, ...)

Prints the given strings to the terminal, by first hiding the readline, printing the message, and showing it again.

This function can be called even when readline has never been initialised.

The last string should end with a newline.


There are some issues with readline that can be problematic in event-based programs:

blocking I/O

Readline uses blocking terminal I/O. Under most circumstances, this does not cause big delays, but ttys have the potential to block programs indefinitely (e.g. on XOFF).

unexpected disk I/O

By default, readline does filename completion on TAB, and reads its config files.

Tab completion can be disabled by calling $rl->unbind_key (9).

tty settings

After readline has been initialised, it will mangle the termios tty settings. This does not normally affect output very much, but should be taken into consideration.

output intermixing

Your program might wish to print messages (for example, log messages) to STDOUT or STDERR. This will usually cause confusion, unless readline is hidden with the hide method.

Oh, and the above list is probably not complete.


 Marc Lehmann <>


rltelnet - a simple tcp_connect-with-readline program using this module.