Tk::TextHighlight - a TextUndo/SuperText widget with syntax highlighting capabilities, can also use Kate languages.

Tk::ROTextHighlight - a Read-only version of this widget.


     use Tk;
     my $haveKateInstalled = 0;
     eval "use Syntax::Highlight::Engine::Kate; \$haveKateInstalled = 1; 1";
     require Tk::TextHighlight;
     my $m = new MainWindow;
     my $e = $m->Scrolled("TextHighlight",
        -syntax => "Perl",
        -scrollbars => "se",
     )->pack(-expand => 1, -fill => "both");
     if ($haveKateInstalled) {
      my ($sections, $kateExtensions) = $e->fetchKateInfo;
     $m->configure(-menu => $e->menu);


Tk::TextHighlight inherits Tk::TextUndo and all its options and methods. Besides syntax highlighting, methods are provided for commenting and uncommenting as well as indenting and unindenting a selected area, matching pairs of braces, brackets and brackets and curlies and automatic indenting of new lines. The included companion module Tk::ROTextHighlight provides all the same functionality in a "readonly" widget for text viewers, etc. Tk::TextHighlight also supports highlighting of all the lauguages of the Syntax::Highlight::Engine::Kate, if that module is installed.

If you want your widget to be read-only, then require Tk::ROTextHighlight, which is based on Tk::ROText instead of Tk::TextUndo.

Syntax highlighting is done through a plugin approach. Adding languages is a matter of writing plugin modules. Theoretically this is not limited to programming languages. The plugin approach could also provide the possibility for grammar or spell checking in spoken languages.

Currently there is support for Bash, HTML, Perl, Pod, Kate, and Xresources.


Name: autoindent
Class: Autoindent
Switch: -autoindent

Boolean, when you press the enter button, should the next line begin at the same position as the current line or not. By default false.

Name: commentchar
Class: Commentchar
Switch: -commentchar

By default "#".

Name: disablemenu
Class: Disablemenu
Switch: -disablemenu

Boolean, by default 0. In case you don't want the menu under the right mouse button to pop up.

Name: highlightInBackground
Class: highlightInBackground
Switch: -highlightInBackground

Whether or not to do highlighting in background freeing up the mouse and keyboard for most events (experimental). May be 1 or 0. Default 0 (Do not highlight in background - block input until highlighting completed).

Name: indentchar
Class: Indentchar
Switch: -indentchar

String to be inserted when the [Tab] key is pressed or when indenting. Default "\t".

Name: match
Class: Match
Switch: -match

string of pairs for brace/bracket/curlie etc matching. If this description doesn't make anything clear, don't worry, the default setting will:


if you don't want matching to be available, simply set it to ''.

Name: matchoptions
Class: Matchoptions
Switch: -matchoptions

Options list for the tag 'Match'. By default:

 [-background => 'red', -foreground => 'yellow']

You can also specify this option as a space separated string. Might come in handy for your Xresource files.

 "-background red -foreground yellow"
Name: not available
Class: not available
Switch -rules

Specify the color and font options for highlighting. You specify a list looking a bit like this.

     ['Tagname1', @options1],
     ['Tagname2', @options2],

The names of the tags are depending on the syntax that is highlighted. See the language modules for more information about this data structure.

Name: rulesdir
Class: Rulesdir
Switch -rulesdir

Specify the directory where this widget stores its coloring defenitions. Files in this directory are stored as "HTML.rules", "Perl.rules" etc. By default it is set to '', which means that when you switch syntax the highlighting rules are not loaded or stored. The hard coded defaults in the language modules will be used.

Name: syntax
Class: Syntax
Switch: -syntax

Specifies the language for highlighting. At this moment the possible values are None, HTML, Perl, Pod Kate:Language, and Xresources. By default None

If Syntax::Highlight::Engine::Kate is installed, you may specify any language that the Kate syntax highlight engine supports.

Alternatively it is possible to specify a reference to your independent plugin.

Name: Not available
Class: Not available
Switch: -updatecall

Here you can specify a callback that will be executed whenever the insert cursor has moved or text has been modified, so your application can keep track of position etc. Don't make this callback to heavy, the widget will get sluggish quickly.

Name: Not available
Class: Not available
Switch: -noPlugInit

Disables TextHighlight feature of initializing default rules when no .rules file present.

Name: Not available
Class: Not available
Switch: -noSyntaxMenu

Don't show the Syntax submenu option in the View submenu of the right-click menu.

Name: Not available
Class: Not available
Switch: -noSaveRulesMenu

Don't show the Save Rules submenu option in the View submenu of the right-click menu.

Name: Not available
Class: Not available
Switch: -noRulesEditMenu

Don't show the Rules Editor option in the View submenu of the right-click menu.

Name: Not available
Class: Not available
Switch: -noRulesMenu

Don't show any of the TextHighlight menu items (combines -noSyntaxMenu, -noRulesEditMenu, and -noSaveRulesMenu options.

There are some undocumented options. They are used internally. It is propably best to leave them alone.



Checks the indention of the previous line and indents the line where the cursor is equally deep.

highlight($begin, $end);

Does syntax highlighting on the section of text indicated by $begin and $end. $begin and $end are linenumbers not indexes!

highlightCheck>($begin, $end);

An insert or delete has taken place affecting the section of text between $begin and $end. highlightCheck is being called after and insert or delete operation. $begin and $end (again linenumbers, not indexes) indicate the section of text affected. highlightCheck checks what needs to be highlighted again and does the highlighting.


Does syntax highlighting on linenumber $line.


Checks wether the appropriate highlight plugin has been loaded. If none or the wrong one is loaded, it loads the correct plugin. It returns a reference to the plugin loaded. It also checks wether the rules have changed. If so, it restarts highlighting from the beginning of the text.


Loads and initalizes a highlighting plugin. First it checks the value of the -syntax option to see which plugin should be loaded. Then it checks wether a set of rules is defined to this plugin in the -rules option. If not, it tries to obtain a set of rules from disk using rulesFetch. If this fails as well it will use the hardcoded rules from the syntax plugin.


Tells the widget that the text from linenumber $line to the end of the text is not to be considered highlighted any more.


Calls visualEnd to see what part of the text is visible on the display, and adjusts highlighting accordingly.


Returns the linenumber part of an index. You may also specify indexes like 'end' or 'insert' etc.


Checks wether the character that is just before the 'insert'-mark should be matched, and if so should it match forwards or backwards. It then calls matchFind.

matchFind($direction, $char, $match, $start, $stop);

Matches $char to $match, skipping nested $char/$match pairs, and displays the match found (if any).


Pops up a window that enables the user to set the color and font options for the current syntax.


Checks wether the file

 $text->cget('-rulesdir') . '/' . $text->cget('-syntax') . '.rules'

exists, and if so attempts to load this as a set of rules.


Saves the currently loaded rules as

 $text->cget('-rulesdir') . '/' . $text->cget('-syntax') . '.rules'

Comment currently selected text.


Indent currently selected text.


Used by the other selection... methods to do the actual work.


Uncomment currently selected text.


Unindent currently selected text.


Allows altering of individual rules by the programmer.


Fetches 3 hashrefs containing information about the installed Kate highlight engine (if installed). The three hashrefs contain in order: The first can be passed to the addkate2viewmenu() method to add the Kate languages to the Syntax.View menu. the keys are "Kate::language" and the values are what's needed to instantiate Kate for that language. the 2nd is a list of file- extension pattern suitable for matching against file-names and the values are the reccomended Kate language for that file-extension. It will return (undef, undef, undef) if Kate is not installed.


Inserts the list of Kate-supported languages to the widget's Syntax.View right-mousebutton popup menu along with the basic TextHight-supported choices. These choices can then be selected to change the current language-highlighting used in the text in the widget. $sections is a hash-ref normally returned as the 1st item in the list returned by fetchKateInfo. NOTE: No menu items will be added if Kate is not installed or if -noRulesMenu or -noSyntaxMenu is set!


This section is a brief description of how the syntax highlighting process works.

Initiating plugin

The highlighting plugin is only then initiated when it is needed. When some highlighting needs to be done, the widget calls highlightPlug to retrieve a reference to the plugin.

highlightPlug checks wether a plugin is present. Next it will check whether the -rules option has been specified or wether the -rules option has changed. If no rules are specified in -rules, it will look for a pathname in the -rulesdir option. If that is found it will try to load a file called '*.rules', where * is the value of -syntax.

If no plugin is present, or the -syntax option has changed value, highlightPlug loads the plugin. and constructs optionally giving it a reference to the found rules as parameter. if no rules are specified, the plugin will use its internal hardcoded defaults.

Changing the rules

A set of rules is a list, containing lists of tagnames, followed by options. If you want to see what they look like, you can have a look at the constructors of each plugin module. Every plugin has a fixed set of tagnames it can handle.

There are two ways to change the rules.

You can invoke the rulesEdit method, which is also available through the View menu. The result is a popup in which you can specify color and font options for each tagname. After pressing 'Ok', the edited rules will be applied. If -rulesdir is specified, the rules will be saved on disk as rulesdir/syntax.rules.

You can also use configure to specify a new set of rules. In this you have ofcause more freedom to use all available tag options. For more details about those there is a nice section about tag options in the Tk::Text documentation. After the call to configure it is wise to call highlightPlug.

Highlighting text

Syntax highlighting is done in a lazy manor. Only that piece of text is highlighted that is needed to present the user a pretty picture. This is done to minimize use of system resources. Highlighting is running on the foreground. Jumping directly to the end of a long fresh loaded textfile may very well take a couple of seconds.

Highlighting is done on a line to line basis. At the end of each line the highlighting status is saved in the list in -colorinf, so when highlighting the next line, the highlight method of TextHighlight will know how to begin.

The line that needs highlighting is offered to the highlight method of the plugin. This method returns a list of offset and tagname pairs. Take for example the following line of perl code.

 my $mother = 'older than i am';

The highlight method of the Perl plugin will return the following list;

 (2 => 'Reserved',    #'my' is a reserved word
  1 => 'DEFAULT',     #Space
  7 => 'Variable',    #$mother
  1 => 'DEFAULT',     #Space
  1 => 'Operator',    #'='
  1 => 'DEFAULT',     #Space
  17 => 'String',     #'older than i am'
  1 => 'DEFAULT',)    #;

The highlight method of TextHighlight will then mark positions 0 to 2 as 'Reserved', positions 2 to 3 as 'DEFAULT', positions 3 to 10 as 'Variable', etcetera.


After writing a couple of plugins myself i have come to a couple of guidelines about how to set them up. If you are interested in adding support for your own syntax highlighting problem or language this section is of interest to you.

From scratch

If you choose to build a plugin completely from scratch, your module needs to meet the following requirements.

 - If you want to write a formal addition to Tk::TextHighlight, 
   your plugin must be in the namespace 
 - The constructor is called 'new', and it should accept 
   a reference a reference to a list of rules as parameters.
 - The following methods will be called upon by Tk::TextHighlight: 
     highlight, stateCompare, rules, setSate, 
     getState, syntax.

More information about those methods is available in the documentation of Tk::TextHighlight::None and Tk::TextHighlight::Template. Good luck, you're on your own now.

Inheriting Tk::TextHighlight::Template

For many highlighting problems Tk::TextHighlight::Template provides a nice basis to start from. Your code could look like this:

 package Tk::TextHighlight::MySyntax;
 use strict;
 use base('Tk::TextHighlight::Template');
 sub new {
    my ($proto, $wdg, $rules) = @_;
    my $class = ref($proto) || $proto;

Next, specify the set of hardcoded rules.

    if (not defined($rules)) {
       $rules =  [
          ['Tagname1', -foreground => 'red'],
          ['Tagname1', -foreground => 'red'],

Call the constructor of Tk::TextHighlight::Template and bless your object.

    my $self = $class->SUPER::new($rules);

So now we have the SUPER class avalable and we can start defining a couple of things.

You could add a couple of lists, usefull for keywords etc.

        'Keywords' => ['foo', 'bar'],
        'Operators' => ['and', 'or'],

For every tag you have to define a corresponding callback like this.

        'Tagname1' => \&Callback1,
        'Tagname2' => \&Callback2,

You have to define a default tagname like this:


Perhaps do a couple of other things but in the end, wrap up the new method.

    bless ($self, $class);
    return $self;

Then you need define the callbacks that are mentioned in the callbacks hash. When you just start writing your plugin i suggest you make them look like this:

 sub callback1 {
    my ($self $txt) = @_;
    return $self->parserError($txt); #for debugging your later additions

Later you add matching statements inside these callback methods. For instance, if you want callback1 to parse spaces it is going to look like this:

 sub callback1 {
    my ($self $txt) = @_;
    if ($text =~ s/^(\s+)//) { #spaces
        $self->snippetParse($1, 'Tagname1'); #the tagname here is optional
        return $text;
    return $self->parserError($txt); #for debugging your later additions

If callback1 is the callback that is called by default, you have to add the mechanism for checking lists to it. Hnce, the code will look like this:

 sub callback1 {
    my ($self $txt) = @_;
    if ($text =~ s/^(\s+)//) { #spaces
        $self->snippetParse($1, 'Tagname1'); #the tagname here is optional
        return $text;
    if ($text =~ s/^([^$separators]+)//) {      #fetching a bare part
        if ($self->tokenTest($1, 'Reserved')) {
            $self->snippetParse($1, 'Reserved');
        } elsif ($self->tokenTest($1, 'Keyword')) {
            $self->snippetParse($1, 'Keyword');
        } else { #unrecognized text
        return $text
    return $self->parserError($txt); #for debugging your later additions

Have a look at the code of Tk::TextHighlight::Bash. Things should clear up. And then, last but not least, you need a syntax method.

Using another module as basis

An example of this approach is the Perl syntax module.

Also with this approach you will have to meet the minimum criteria as set out in the From scratch section.


If you have written a plugin, i will be happy to include it in the next release of Tk::TextHighlight. If you send it to me, please have it accompanied with the sample of code that you used for testing.


Jim Turner (turnerjw784 - att.symbol.thingy -

This is a derived work from Tk::CodeText, by Hans Jeuken (haje - att.symbol.thingy -

Thanks go to Mr. Hans Jeuken for his great work in making this and the Kate modules possible. He did the hard work!


Unknown. If you find any, please contact the author.


Add additional language modules. I am going to need help on this one. We currently support all the original Tk::CodeText languages (included) plus all those supported by Syntax::Highlight::Engine::Kate, if it's installed.
The sample files in the test suite should be set up so that conformity with the language specification can actually be verified.


Tk::Text, Tk::TextUndo, Tk::Text::SuperText, Tk::TextHighlight::Bash, Tk::CodeText, Syntax::Highlight::Perl::Improved, Syntax::Highlight::Engine::Kate