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Author image Marek Rouchal


Term::Completion - read one line of user input, with convenience functions


  use Term::Completion;
  my $tc = Term::Completion->new(
    prompt  => "Enter your first name: ",
    choices => [ qw(Alice Bob Chris Dave Ellen) ]
  my $name = $tc->complete();
  print "You entered: $name\n";


Term::Completion is an extensible, highly configurable replacement for the venerable Term::Complete package. It is object-oriented and thus allows subclassing. Two derived classes are Term::Completion::Multi and Term::Completion::Path.

A prompt is printed and the user may enter one line of input, submitting the answer by pressing the ENTER key. This basic scenario can be implemented like this:

    my $answer = <STDIN>;
    chomp $answer;

But often you don't want the user to type in the full word (from a list of choices), but allow completion, i.e. expansion of the word as far as possible by pressing as few keys as necessary.

Some users like to cycle through the choices, preferably with the up/down arrow keys.

And finally, you may not want the user to enter any random characters, but validate what was enter and come back if the entry did not pass the validation.

If you are missing full line editing (left/right, delete to the left and right, jump to the beginning and the end etc.), you are probably wrong here, and want to consider Term::ReadLine and friends.

Global Setup

The technical challenge for this package is to read single keystrokes from the input handle - usually STDIN, the user's terminal. There are various ways how to accomplish that, and Term::Completion supports them all:

use Term::Completion qw(:stty);

Use the external stty command to configure the terminal. This is what Term::Complete does, and works fine on systems that have a working stty. However, using an external command seems like an ugly overhead. See also Term::Completion::_stty.

use Term::Completion qw(:readkey);

This is the default for all systems, as we assume you have Term::ReadKey installed. This seems to be the right approach to also support various platforms. See also Term::Completion::_readkey.

use Term::Completion qw(:POSIX);

This uses the POSIX interface (POSIX::Termios) to set the terminal in the right mode. It should be well portable on UNIX systems. See also Term::Completion::_POSIX.


Term::Completion does not export anything by default, in order not to pollute your namespace. Here are the exportable methods:


For compatibility with Term::Complete, you can import the Complete function:

  use Term::Completion qw(Complete);
  my $result = Complete($prompt, @choices);


Term::Completion objects are simple hashes. All fields are fully accessible and can be tweaked directly, without accessor methods.

Term::Completion offers the following methods:


The constructor for Term::Completion objects. Arguments are key/value pairs. See "Configuration" for a description of all options. Note that columns and rows overrides the real terminal size from Term::Size.

Usually you'd supply the list of choices and the prompt string:

  my $tc = Term::Completion->new(
    prompt => "Pick a color: ",
    choices => [ qw(red green blue) ]

The object can be reused several times for the same purpose. Term::Completion objects are simple hashes. All fields are fully accessible and can be tweaked directly, without accessor methods. In the example above, you can manipulate the choice list:

  push(@{$tc->{choices}}, qw(cyan magenta yellow));

Note that the constructor won't actually execute the query - that is done by the complete() method.


This method executes the query and returns the result string. It is guaranteed that the result is a defined value, it may however be empty or 0.


This method is called on the answer string entered by the user after the ENTER key was pressed. The implementation in the base class is just stripping any leading and trailing whitespace. The method returnes the postprocessed answer string.


This method is called on the postprocessed answer and returns:

1. in case of success

The correct answer string. Please note that the validate method may alter the answer, e.g. to adapt it to certain conventions (lowercase only).

2. in case of failure

The undef value. This indicates a failure of the validation. In that situation an error message should be printed to tell the user why the validation failed. This should be done using the following idiom for maximum portability:

  $this->{out}->print("ERROR: no such choice available",

Validation is turned on by the validation parameter. See "Predefined Validations" for a list of available validation options.

You can override this method in derived classes to implement your own validation strategy - but in some situations this could be too much overhead. So the base class understands this callback:

  my $tc = Term::Completion->new(
    prompt => 'Enter voltage: ',
    choices => [ qw(1.2 1.5 1.8 2.0 2.5 3.3) ],
    validate => [
      'Voltage must be a positive, non-zero value' =>
      sub { $_[0] > 0.0 ? $_[0] : undef }

Note that the given code reference will be passed the one single argument, namely the current input string, and is supposed to return undef if the input is invalid, or the (potentially corrected) string, like in the example above.


This method returns the items from the choice list which match the current answer string. This method is used by the completion algorithm and the list of choices. This can be overridden to implement a completely different way to get the choices (other than a static list) - e.g. by querying a database.


This method is called when the user types CTRL-D (or TAB-TAB) to show the list of choices, available with the current answer string. Basically get_choices($answer) is called and then the list is pretty-printed using _show_choices(...).


Pretty-print the list of items given as arguments. The list is formatted into columns, like in UNIX' ls command, according to the current terminal width (if Term::Size is available). If the list is long, then poor man's paging is enabled, comparable to the UNIX more command. The user can use ENTER to proceed by one line, SPACE to proceed to the next page and Q or CTRL-C to quit paging. After listing the choices and return from this method, the prompt and the current answer are redisplayed.

Override this method if you have a better pretty-printer/pager. :-)


There is a global hash %Term::Completion::DEFAULTS that contains the default values for all configurable options. Upon object construction (see "new(...)" any of these defaults can be overridden by placing the corresponding key/value pair in the arguments. Find below the list of configurable options, their default value and their purpose.

The key definitions are regular expressions (qr/.../) - this allows to match multiple keys for the same action, as well as disable the action completely by specifying an expression that will never match a single character, e.g. qr/-disable-/.


The input file handle, default is \*STDIN. Can be any filehandle-like object, has to understand the getc() method.


The output file handle, default is \*STDOUT. Can be basically any filehandle-like object, has to understand the print() method.


Regular expression matching those keys that should work as the TAB key, i.e. complete the current answer string as far as possible, and when pressed twice, show the list of matching choices. Default is the tab key, i.e. qr/\t/.


Regular expression matching those keys that should trigger the listing of choices. Default is - like in Term::Complete - CTRL-D, i.e. qr/\cd/.


Regular expression matching those keys that should delete all input. Default is CTRL-U, i.e. qr/\cu/.


Regular expression matching those keys that should delete one character (backspace). Default is the BACKSPACE and the DELETE keys, i.e. qr/[\177\010]/.


This is a special control: if either sep or delim are defined (see below), then this key "wipes" all characters (from the right) until (and including) the last separator or delimiter. Default is CTRL-W, i.e. qr/\cw/.


Regular expression matching those keys that finish the entry process. Default is the ENTER key, and for paranoia reasons we use qr/[\r\n]/.


Regular expression matching those keys that select the previous item from the choice list. Default is CTRL-P, left and up arrow keys, i.e. qr/\cp|\x1b\[[AD]/.


Regular expression matching those keys that select the next item from the choice list. Default is CTRL-N, right and down arrow keys, i.e. qr/\cn|\x1b\[[BC]/.


Regular expression matching those keys that exit from paging when the list of choices is displayed. Default is 'q' and CTRL-C, i.e. qr/[\ccq]/.


A default prompt string to apply for all Term::Completion objects. Default is the empty string.


Default number of terminal columns for the list of choices. This default is only applicable if Term::Size is unavailable to get the real number of columns. The default is 80.


Default number of terminal rows for the list of choices. This default is only applicable if Term::Size is unavailable to get the real number of rows. The default is 24. If set to 0 (zero) there won't be any paging when the list of choices is displayed.


The character which rings the terminal bell, default is "\a". Used when completing with the TAB key and there are multiple choices available, and when paging is restarted because the terminal size was changed.


The string to display when max number of lines on the terminal has been reached when displaying the choices. Default is '--more--'.


The characters to print for a new line in raw terminal mode. Default is "\r\n".


The characters to print for deleting one character (to the left). Default is "\b \b".


Regular expression matching those keys that print helptext on-demand. Furthermore, with help defined (undef), automatic printing of helptext by the complete() method is disabled (enabled). Default is undef, for backwards compatibility; qr/\?/ is suggested.


This is an optional text which is printed by the complete() method before the actual completion process starts, unless help is defined. It may be a multi-line string and should end with a newline character. Default is undef. The text could for example look like this:

  helptext => <<'EOT',
    You may use the following control keys here:
      TAB      complete the word
      CTRL-D   show list of matching choices (same as TAB-TAB)
      CTRL-U   delete the entire input
      CTRL-H   delete a character (backspace)
      CTRL-P   cycle through choices (backward) (also up arrow)
      CTRL-N   cycle through choices (forward) (also down arrow)

The default list of choices for all Term::Completion objects (unless overridden by the new(...) constructor. Has to be an array reference. Default is the empty array reference []. Undefined items are filtered out.

Predefined Validations

Whenever you need validation of the user's input, you can always specify your own code, see "validate($answer)" above. To support everybody's laziness, there are a couple of predefined validation methods available. You can specify them as a blank or comma separated string in the new(...) constructor:

  my $tc = Term::Completion->new(
    prompt => 'Fruit: ',
    choices => [ qw(apple banana cherry) ],
    validation => 'nonblank fromchoices'

In the example above, you are guaranteed the user will choose one of the given choices. Here's a list of all pre-implemented validations:


Map all the answer string to upper case before proceeding with any further validation.


Map all the answer string to lower case before proceeding with any further validation.


This option has some magic: it tries to match the answer string first at the beginning of all choices; if that yields a unique match, the match is returned. If not, the answer string is matched at any position in the choices, and if that yields a unique match, the match is returned. Otherwise an error will be raised that the answer does not match a unique item.


Raises an error if the answer has a length of zero characters.


Raises an error if the answer does not contain any non-whitespace character.


Only allow literal entries from the choice list, or the empty string. If you don't like the latter, combine this with nonempty.


Only allow numeric values, e.g. -1.234 or 987.


Only allow integer numbers, e.g. -1 or 234.


Prohibit the numeric value 0 (zero). To avoid warnings about non-numeric values, this should be used together with one of numeric or integer.


Only allow numeric values greater than zero. To avoid warnings about non-numeric values, this should be used together with one of numeric or integer.

This list obviously can be arbitrarily extended. Suggestions (submitted as patches) are welcome.


Terminal handling

This package temporarily has to set the terminal into 'raw' mode, which means that all keys lose their special meaning (like CTRL-C, which normally interrupts the script). This is a highly platform-specific operation, and therefore this package depends on the portability of Term::ReadKey and POSIX. Reports about failing platforms are welcome, but there is probably little that can be fixed here.

Terminal size changes

This package does the best it can to handle changes of the terminal size during the completion process. It redisplays the prompt and the current entry during completion, and restarts paging when showing the list of choices. The latter however only after you press a key - the bell sounds to indicate that something happened. This is because it does not seem possible to jump out of a getc().

Arrow key handling

On UNIX variants, the arrow keys generate a sequence of bytes, starting with the escape character, followed by a square brackets and others. Term::Completion accumulates these characters until they either match this sequence, or not. In the latter case, it will drop the previous characters and proceed with the last one typed. That however means that you won't be able to assign the bare escape key to an action. I found this to be the lesser of the evils. Suggestions on how to solve this in a clean way are welcome. Yes, I read "How can I tell whether there's a character waiting on a filehandle?" in perlfaq5 but that's probably little portable.


Term::Complete, Term::ReadKey, Term::Size, POSIX, Term::ReadLine


Marek Rouchal, <marekr@cpan.org<gt>


Please submit patches, bug reports and suggestions via the CPAN tracker http://rt.cpan.org.


Copyright (C) 2009-2013 by Marek Rouchal

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.8 or, at your option, any later version of Perl 5 you may have available.