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Perl 5 version 20.0 documentation
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Term::ReadLine - Perl interface to various readline packages. If no real package is found, substitutes stubs instead of basic functions.


  1. use Term::ReadLine;
  2. my $term = Term::ReadLine->new('Simple Perl calc');
  3. my $prompt = "Enter your arithmetic expression: ";
  4. my $OUT = $term->OUT || \*STDOUT;
  5. while ( defined ($_ = $term->readline($prompt)) ) {
  6. my $res = eval($_);
  7. warn $@ if $@;
  8. print $OUT $res, "\n" unless $@;
  9. $term->addhistory($_) if /\S/;
  10. }


This package is just a front end to some other packages. It's a stub to set up a common interface to the various ReadLine implementations found on CPAN (under the Term::ReadLine::* namespace).

Minimal set of supported functions

All the supported functions should be called as methods, i.e., either as

  1. $term = Term::ReadLine->new('name');

or as

  1. $term->addhistory('row');

where $term is a return value of Term::ReadLine->new().

  • ReadLine

    returns the actual package that executes the commands. Among possible values are Term::ReadLine::Gnu , Term::ReadLine::Perl , Term::ReadLine::Stub .

  • new

    returns the handle for subsequent calls to following functions. Argument is the name of the application. Optionally can be followed by two arguments for IN and OUT filehandles. These arguments should be globs.

  • readline

    gets an input line, possibly with actual readline support. Trailing newline is removed. Returns undef on EOF .

  • addhistory

    adds the line to the history of input, from where it can be used if the actual readline is present.

  • IN , OUT

    return the filehandles for input and output or undef if readline input and output cannot be used for Perl.

  • MinLine

    If argument is specified, it is an advice on minimal size of line to be included into history. undef means do not include anything into history. Returns the old value.

  • findConsole

    returns an array with two strings that give most appropriate names for files for input and output using conventions "<$in" , ">out" .

  • Attribs

    returns a reference to a hash which describes internal configuration of the package. Names of keys in this hash conform to standard conventions with the leading rl_ stripped.

  • Features

    Returns a reference to a hash with keys being features present in current implementation. Several optional features are used in the minimal interface: appname should be present if the first argument to new is recognized, and minline should be present if MinLine method is not dummy. autohistory should be present if lines are put into history automatically (maybe subject to MinLine ), and addhistory if addhistory method is not dummy.

    If Features method reports a feature attribs as present, the method Attribs is not dummy.

Additional supported functions

Actually Term::ReadLine can use some other package, that will support a richer set of commands.

All these commands are callable via method interface and have names which conform to standard conventions with the leading rl_ stripped.

The stub package included with the perl distribution allows some additional methods:

  • tkRunning

    makes Tk event loop run when waiting for user input (i.e., during readline method).

  • event_loop

    Registers call-backs to wait for user input (i.e., during readline method). This supersedes tkRunning.

    The first call-back registered is the call back for waiting. It is expected that the callback will call the current event loop until there is something waiting to get on the input filehandle. The parameter passed in is the return value of the second call back.

    The second call-back registered is the call back for registration. The input filehandle (often STDIN, but not necessarily) will be passed in.

    For example, with AnyEvent:

    1. $term->event_loop(sub {
    2. my $data = shift;
    3. $data->[1] = AE::cv();
    4. $data->[1]->recv();
    5. }, sub {
    6. my $fh = shift;
    7. my $data = [];
    8. $data->[0] = AE::io($fh, 0, sub { $data->[1]->send() });
    9. $data;
    10. });

    The second call-back is optional if the call back is registered prior to the call to $term->readline.

    Deregistration is done in this case by calling event_loop with undef as its parameter:

    1. $term->event_loop(undef);

    This will cause the data array ref to be removed, allowing normal garbage collection to clean it up. With AnyEvent, that will cause $data->[0] to be cleaned up, and AnyEvent will automatically cancel the watcher at that time. If another loop requires more than that to clean up a file watcher, that will be up to the caller to handle.

  • ornaments

    makes the command line stand out by using termcap data. The argument to ornaments should be 0, 1, or a string of a form "aa,bb,cc,dd" . Four components of this string should be names of terminal capacities, first two will be issued to make the prompt standout, last two to make the input line standout.

  • newTTY

    takes two arguments which are input filehandle and output filehandle. Switches to use these filehandles.

One can check whether the currently loaded ReadLine package supports these methods by checking for corresponding Features .




The environment variable PERL_RL governs which ReadLine clone is loaded. If the value is false, a dummy interface is used. If the value is true, it should be tail of the name of the package to use, such as Perl or Gnu .

As a special case, if the value of this variable is space-separated, the tail might be used to disable the ornaments by setting the tail to be o=0 or ornaments=0 . The head should be as described above, say

If the variable is not set, or if the head of space-separated list is empty, the best available package is loaded.

  1. export "PERL_RL=Perl o=0" # Use Perl ReadLine sans ornaments
  2. export "PERL_RL= o=0" # Use best available ReadLine sans ornaments

(Note that processing of PERL_RL for ornaments is in the discretion of the particular used Term::ReadLine::* package).