POE::Wheel::ReadLine(3User Contributed Perl DocumentatiPOE::Wheel::ReadLine(3)NAMEPOE::Wheel::ReadLine - non-blocking Term::ReadLine for POE
SYNOPSIS
#!perl
use warnings;
use strict;
use POE qw(Wheel::ReadLine);
POE::Session->create(
inline_states=> {
_start => \&setup_console,
got_user_input => \&handle_user_input,
}
);
POE::Kernel->run();
exit;
sub handle_user_input {
my ($input, $exception) = @_[ARG0, ARG1];
my $console = $_[HEAP]{console};
unless (defined $input) {
$console->put("$exception caught. B'bye!");
$_[KERNEL]->signal($_[KERNEL], "UIDESTROY");
$console->write_history("./test_history");
return;
}
$console->put(" You entered: $input");
$console->addhistory($input);
$console->get("Go: ");
}
sub setup_console {
$_[HEAP]{console} = POE::Wheel::ReadLine->new(
InputEvent => 'got_user_input'
);
$_[HEAP]{console}->read_history("./test_history");
$_[HEAP]{console}->clear();
$_[HEAP]{console}->put(
"Enter some text.",
"Ctrl+C or Ctrl+D exits."
);
$_[HEAP]{console}->get("Go: ");
}
DESCRIPTIONPOE::Wheel::ReadLine is a non-blocking form of Term::ReadLine that's
compatible with POE. It uses Term::Cap to interact with the terminal
display and Term::ReadKey to interact with the keyboard.
POE::Wheel::ReadLine handles almost all common input editing keys. It
provides an input history list. It has both vi and emacs modes. It
supports incremental input search. It's fully customizable, and it's
compatible with standard readline(3) implementations such as
Term::ReadLine::Gnu.
POE::Wheel::ReadLine is configured by placing commands in an "inputrc"
initialization file. The file's name is taken from the "INPUTRC"
environment variable, or ~/.inputrc by default. POE::Wheel::ReadLine
will read the inputrc file and configure itself according to the
commands and variables therein. See readline(3) for details about
inputrc files.
The default editing mode will be emacs-style, although this can be
configured by setting the 'editing-mode' variable within an inputrc
file. If all else fails, POE::Wheel::ReadLine will determine the
user's favorite editor by examining the EDITOR environment variable.
PUBLIC METHODS
Constructor
Most of POE::Wheel::ReadLine's interaction is through its constructor,
new().
new
new() creates and returns a new POE::Wheel::ReadLine object. Be sure
to instantiate only one, as multiple console readers would conflict.
InputEvent
"InputEvent" names the event that will indicate a new line of console
input. See "PUBLIC EVENTS" for more details.
PutMode
"PutMode" controls how output is displayed when put() is called during
user input.
When set to "immediate", put() pre-empts the user immediately. The
input prompt and user's input to date are redisplayed after put() is
done.
The "after" "PutMode" tells put() to wait until after the user enters
or cancels her input.
Finally, "idle" will allow put() to pre-empt user input if the user
stops typing for "IdleTime" seconds. This mode behaves like "after" if
the user can't stop typing long enough. This is POE::Wheel::ReadLine's
default mode.
IdleTime
"IdleTime" tells POE::Wheel::ReadLine how long the keyboard must be
idle before "put()" becomes immediate or buffered text is flushed to
the display. It is only meaningful when "PutMode" is "idle".
"IdleTime" defaults to 2 seconds.
AppName
"AppName" registers an application name which is used to retrieve
application-specific key bindings from the inputrc file. The default
"AppName" is "poe-readline".
# If using POE::Wheel::ReadLine, set
# the key mapping to emacs mode and
# trigger debugging output on a certain
# key sequence.
$if poe-readline
set keymap emacs
Control-xP: poe-wheel-debug
$endif
History List Management
POE::Wheel::ReadLine supports an input history, with searching.
add_history
add_history() accepts a list of lines to add to the input history.
Generally it's called with a single line: the last line of input
received from the terminal. The "SYNOPSIS" shows add_history() in
action.
get_history
get_history() returns a list containing POE::Wheel::ReadLine's current
input history. It may not contain everything entered into the wheel
write_history
write_history() writes the current input history to a file. It accepts
one optional parameter: the name of the file where the input history
will be written. write_history() will write to ~/.history if no file
name is specified.
Returns true on success, or false if not.
The "SYNOPSIS" shows an example of write_history() and the
corresponding read_history().
read_history
read_history(FILENAME, START, END) reads a previously saved input
history from a named file, or from ~/.history if no file name is
specified. It may also read a subset of the history file if it's given
optional START and END parameters. The file will be read from the
beginning if START is omitted or zero. It will be read to the end if
END is omitted or earlier than START.
Returns true on success, or false if not.
The "SYNOPSIS" shows an example of read_history() and the corresponding
write_history().
Read the first ten history lines:
$_[HEAP]{console}->read_history("filename", 0, 9);
history_truncate_file
history_truncate_file() truncates a history file to a certain number of
lines. It accepts two parameters: the name of the file to truncate,
and the maximum number of history lines to leave in the file. The
history file will be cleared entirely if the line count is zero or
omitted.
The file to be truncated defaults to ~/.history. So calling
history_truncate_file() with no parameters clears ~/.history.
Returns true on success, or false if not.
Note that history_trucate_file() removes the earliest lines from the
file. The later lines remain intact since they were the ones most
recently entered.
Keep ~/.history down to a manageable 100 lines:
$_[HEAP]{console}->history_truncate_file(undef, 100);
Key Binding Methods
bind_key
bind_key(KEYSTROKE, FUNCTION) binds a FUNCTION to a named KEYSTROKE
sequence. The keystroke sequence can be in any of the forms defined
within readline(3). The function should either be a pre-defined name,
such as "self-insert" or a function reference. The binding is made in
the current keymap. Use the rl_set_keymap() method to change keymaps,
if desired.
add_defun NAME FN
add_defun(NAME, FUNCTION) defines a new global FUNCTION, giving it a
specific NAME. The function may then be bound to keystrokes by that
NAME.
Console I/O Methods
clear
Clears the terminal.
terminal_size
Returns what POE::Wheel::ReadLine thinks are the current dimensions of
the terminal. Returns a list of two values: the number of columns and
number of rows, respectively.
sub some_event_handler {
my ($columns, $rows) = $_[HEAP]{console}->terminal_size;
$_[HEAP]{console}->put(
"Terminal columns: $columns",
"Terminal rows: $rows",
);
}
get
get() causes POE::Wheel::ReadLine to display a prompt and then wait for
input. Input is not noticed unless get() has enabled the wheel's
internal I/O watcher.
After get() is called, the next line of input or exception on the
console will trigger an "InputEvent" with the appropriate parameters.
POE::Wheel::ReadLine will then enter an inactive state until get() is
called again.
Calls to get() without an argument will preserve the current prompt.
Calling get() with an argument before a whole line of input is received
will change the prompt on the fly.
See the "SYNOPSIS" for sample usage.
put
put() accepts a list of lines to put on the terminal.
POE::Wheel::ReadLine is line-based. See POE::Wheel::Curses for more
funky display options.
Please do not use print() with POE::Wheel::ReadLine. print()
invariably gets the newline wrong, leaving an application's output to
stairstep down the terminal. Also, put() understands when a user is
entering text, and "PutMode" may be used to avoid interrupting the
user.
ReadLine Option Methods
attribs
attribs() returns a reference to a hash of readline options. The
returned hash may be used to query or modify POE::Wheel::ReadLine's
behavior.
option
option(NAME) returns a specific member of the hash returned by
attribs(). It's a more convenient way to query POE::Wheel::ReadLine
options.
PUBLIC EVENTSPOE::Wheel::ReadLine emits only a single event.
InputEvent
"InputEvent" names the event that will be emitted upon any kind of
complete terminal input. Every "InputEvent" handler receives three
parameters:
$_[ARG0] contains a line of input. It may be an empty string if the
user entered an empty line. An undefined $_[ARG0] indicates some
exception such as end-of-input or the fact that the user canceled their
input or pressed C-c (^C).
$_[ARG1] describes an exception, if one occurred. It may contain one
of the following strings:
cancel
The "cancel" exception indicates when a user has canceled a line of
input. It's sent when the user triggers the "abort" function, which
is bound to C-g (^G) by default.
eot
"eot" is the ASCII code for "end of tape". It's emitted when the
user requests that the terminal be closed. By default, it's
triggered when the user presses C-d (^D) on an empty line.
interrupt
"interrupt" is sent as a result of the user pressing C-c (^C) or
otherwise triggering the "interrupt" function.
Finally, $_[ARG2] contains the ID for the POE::Wheel::ReadLine object
that sent the "InputEvent".
CUSTOM BINDINGSPOE::Wheel::ReadLine allows custom functions to be bound to keystrokes.
The function must be made visible to the wheel before it can be bound.
To register a function, use POE::Wheel::ReadLine's add_defun() method:
POE::Wheel::ReadLine->add_defun('reverse-line', \&reverse_line);
When adding a new defun, an optional third parameter may be provided
which is a key sequence to bind to. This should be in the same format
as that understood by the inputrc parsing.
Bound functions receive three parameters: A reference to the wheel
object itself, the key sequence that triggered the function (in
printable form), and the raw key sequence. The bound function is
expected to dig into the POE::Wheel::ReadLine data members to do its
work and display the new line contents itself.
This is less than ideal, and it may change in the future.
CUSTOM COMPLETION
An application may modify POE::Wheel::ReadLine's "completion_function"
in order to customize how input should be completed. The new
completion function must accept three scalar parameters: the word being
completed, the entire input text, and the position within the input
text of the word being completed.
The completion function should return a list of possible matches. For
example:
my $attribs = $wheel->attribs();
$attribs->{completion_function} = sub {
my ($text, $line, $start) = @_;
return qw(a list of candidates to complete);
}
This is the only form of completion currently supported.
IMPLEMENTATION DIFFERENCES
Although POE::Wheel::ReadLine is modeled after the readline(3) library,
there are some areas which have not been implemented. The only option
settings which have effect in this implementation are: bell-style,
editing-mode, isearch-terminators, comment-begin, print-completions-
horizontally, show-all-if-ambiguous and completion_function.
The function 'tab-insert' is not implemented, nor are tabs displayed
properly.
SEE ALSO
POE::Wheel describes the basic operations of all wheels in more depth.
You need to know this.
readline(3), Term::Cap, Term::ReadKey.
The SEE ALSO section in POE contains a table of contents covering the
entire POE distribution.
Term::Visual is an alternative to POE::Wheel::ReadLine. It provides
scrollback and a status bar in addition to editable user input.
Term::Visual supports POE despite the lack of "POE" in its name.
BUGSPOE::Wheel::ReadLine has some known issues:
Perl 5.8.0 is Broken
Non-blocking input with Term::ReadKey does not work with Perl 5.8.0,
especially on Linux systems for some reason. Upgrading Perl will fix
things. If you can't upgrade Perl, consider alternative input methods,
such as Term::Visual.
<http://rt.cpan.org/Ticket/Display.html?id=4524> and related tickets
explain the issue in detail. If you suspect your system is one where
Term::ReadKey fails, you can run this test program to be sure.
#!/usr/bin/perl
use Term::ReadKey;
print "Press 'q' to quit this test.\n";
ReadMode 5; # Turns off controls keys
while (1) {
while (not defined ($key = ReadKey(-1))) {
print "Didn't get a key. Sleeping 1 second.\015\012";
sleep (1);
}
print "Got key: $key\015\012";
($key eq 'q') and last;
}
ReadMode 0; # Reset tty mode before exiting
exit;
Non-Optimal Code
Dissociating the input and display cursors introduced a lot of code.
Much of this code was thrown in hastily, and things can probably be
done with less work.
Unimplemented Features
Input editing is not kept on one line. If it wraps, and a terminal
cannot wrap back through a line division, the cursor will become lost.
Unicode support. I feel real bad about throwing away native
representation of all the 8th-bit-set characters. I also have no idea
how to do this, and I don't have a system to test this. Patches are
very much welcome.
GOTCHAS / FAQ
Lost Prompts
Q: Why do I lose my prompt every time I send output to the screen?
A: You probably are using print or printf to write screen output.
ReadLine doesn't track STDOUT itself, so it doesn't know when to
refresh the prompt after you do this. Use ReadLine's put() method to
write lines to the console.
Edit Keystrokes Display as ^C
Q: None of the editing keystrokes work. Ctrl-C displays "^c" rather
than generating an interrupt. The arrow keys don't scroll through my
input history. It's generally a bad experience.
A: You're probably a vi/vim user. In the absence of a ~/.inputrc file,
POE::Wheel::ReadLine checks your EDITOR environment variable for clues
about your editing preference. If it sees /vi/ in there, it starts in
vi mode. You can override this by creating a ~/.inputrc file
containing the line "set editing-mode emacs", or adding that line to
your existing ~/.inputrc. While you're in there, you should totally
get acquainted with all the other cool stuff you can do with .inputrc
files.
Lack of Windows Support
Q: Why doesn't POE::Wheel::ReadLine work on Windows? Term::ReadLine
does.
A: POE::Wheel::ReadLine requires select(), because that's what POE uses
by default to detect keystrokes without blocking. About half the
flavors of Perl on Windows implement select() in terms of the same
function in the WinSock library, which limits select() to working only
with sockets. Your console isn't a socket, so select() doesn't work
with your version of Perl on Windows.
Really good workarounds are possible but don't exist as of this
writing. They involve writing a special POE::Loop for Windows that
either uses a Win32-specific module for better multiplexing, that polls
for input, or that uses blocking I/O watchers in separate threads.
Cygwin Support
Q: Why does POE::Wheel::ReadLine complain about my "dumb" terminal?
A: Do you have Strawberry Perl installed? Due to the way it works, on
installation it sets a global environment variable in MSWin32 for
TERM=dumb. ( it may be fixed in a future version, but it's here to stay
for now, ha! ) In this case, logging into the Cygwin shell via the
cygwin.bat launcher results in a nonfunctional readline.
Normally, Cygwin will set TERM=cygwin in the launcher. However, if the
TERM was already set it will not alter the value. Hence, the "bug"
appears! What you can do is to hack the cygwin.bat file to add this
line:
SET TERM=cygwin
Other users reported that you can have better results by editing the
~/.bash_profile file to set TERM=cygwin because on a Cygwin upgrade it
overwrites the cygwin.bat file.
Alternatively, you could install different terminals like "xterm" or
"rxvt" as shown here: <http://c2.com/cgi/wiki?BetterCygwinTerminal>.
Please let us know if you encounter problems using any terminal other
than "dumb".
If you feel brave, you can peruse the RT ticket at
<http://rt.cpan.org/Ticket/Display.html?id=55365> for more information
on this problem.
AUTHORS & COPYRIGHTSPOE::Wheel::ReadLine was originally written by Rocco Caputo.
Nick Williams virtually rewrote it to support a larger subset of GNU
readline.
Please see POE for more information about other authors and
contributors.
POD ERRORS
Hey! The above document had some coding errors, which are explained
below:
Around line 3222:
A non-empty Z<>
Around line 3500:
A non-empty Z<>
Around line 3502:
A non-empty Z<>
perl v5.14.2 2011-12-15 POE::Wheel::ReadLine(3)
