Perl/Tk FAQ

Copyright (c) 1995-1996 Nick Ing-Simmons. All rights reserved.
This package is free software; you can redistribute it and/or
modify it under the same terms as Perl itself, with the exception
of the files in the pTk sub-directory which have separate terms
derived from those of the orignal Tk4.0 sources and/or Tix.

IN NO EVENT SHALL THE AUTHORS OR DISTRIBUTORS BE LIABLE TO ANY PARTY
FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
ARISING OUT OF THE USE OF THIS SOFTWARE, ITS DOCUMENTATION, OR ANY
DERIVATIVES THEREOF, EVEN IF THE AUTHORS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.

THE AUTHORS AND DISTRIBUTORS SPECIFICALLY DISCLAIM ANY WARRANTIES,
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT.  THIS SOFTWARE
IS PROVIDED ON AN "AS IS" BASIS, AND THE AUTHORS AND DISTRIBUTORS HAVE
NO OBLIGATION TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR
MODIFICATIONS.

See pTk/license.terms for details of this Tk license, 
and pTk/Tix.license for the Tix license.

This compilation of Frequently Asked Questions & answers (FAQ) is intended to answer several of the first (and largely more basic) questions posted to the comp.lang.perl.tk newsgroup and the ptk mailing list.

This document concerns itself with the Perl/Tk programming language (or, if you prefer, the Tk extension to Perl). Please be aware that this is not the Perl FAQ, this is not the Tcl FAQ, nor is this the Tcl/Tk FAQ. Each of those other documents is a useful source of information for Perl/Tk programmers but they are completely different from this one.

This is a dynamic document and contributions, clarifications, and corrections are most welcome! Please send e-mail to <pvhp@lns62.lns.cornell.edu> or to <pvhp@forte.com>. With your help this document will get better (-:

perl/Tk FAQ

1. What is perl/Tk?
2. What is the difference between perl/Tk and Tkperl?
3. Do I need Tcl/Tk in order to build Perl/Tk?
4. Where is it?
5. What/Where is CPAN?
6. How do I build it?
7. Where is the Documentation?
8. How do I write scripts in perl/Tk?
9. What widget types are available under perl/Tk?
10. How do I get widget X to do Y ?
    1. How do I get a Button to call a Perl subroutine?
    2. How do I get a Button to actively change under my mouse pointer?
    3. How do I arrange the layout of my widgets?
    4. How do I get a Popup to popup?
    5. How do I bind keyboard keys?
    6. How do I add bindings?
    7. How do I bind the action of a slider (sic) to ... ?
    8. How do I configure a Scrollbar to scroll multiple widgets?
    9. How do I display a bitmap?
    10. How do I display an image?
    11. What Image types are available?
    12. Is there any way to have more than one Listbox contain a selection?
    13. How do I select a range of tags in a Text widget?
    14. How do I group Radiobuttons together?
    15. How do I specify fonts?
    16. How do I get the entry in an Entry?
    17. How do I hide a password Entry?
    18. How do I limit an Entry's insertion width?
    19. How do I obtain Menus that do not tear off?
11. How do I get a Canvas to ... ?
    1. Display a bitmap?
    2. Erase a display?
    3. Display an Image?
    4. What things can be created on a Canvas?
    5. How do I redraw a line on a Canvas?
    6. How do I use the Canvas as a geometry manager?
    7. How do I get a Canvas to output PostScript(c)?
    8. How do I get a PostScript(c) output of a Canvas w/ widgets?
    9. How do I get the size of a Canvas? After a re-size?
    10. How do I bind different actions to different areas of the same Canvas?
12. Common Problems.
    1. What do the ->, => and :: symbols mean?
    2. What happened to the ampersands &?
    3. What happened to the quotation marks?
    4. Must I use "my" on all my variables?
    5. Is there a way to find out what is in my perl/Tk "PATH"?
    6. What is the difference between use and require?
    7. How do I change the cursor/color?
    8. How do I ring the bell?
    9. How do I determine the version of perl/Tk that I am running?
    10. How do I call perl from C?
    11. How do I call Tcl code from perl/Tk?
13. What are some of the primary differences between Tcl/Tk and Perl/Tk?
14. How do I install new scripts | modules | extensions?
15. How do I write new modules?
16. Composite Widgets.
    1. How do I get a Dialog box?
    2. Is there a file selector?
    3. Is there a color editor?
    4. Is there a round Scale?
    5. Is there something equivalent to tkerror?
    6. Are there Tables?
17. Programming/development tools.
    1. Is there a Tcl/Tk to perl/Tk translator?
    2. Is there something equivalent to wish in perl/Tk?
    3. Is there a debugger specifically for perl/Tk?
    4. Is there a GUI builder in perl/Tk?
18. Processes & Inter-Process Communication under Perl/Tk.
    1. How does one get Perl/Tk to act on events that are not coming from X?
    2. Is there a send and do I need xauth?
    3. How can I do animations using after?
    4. How do I update widgets while waiting for other processes to complete?
    5. How do you fork on System V (HP)?
19. How do I "clear the screen"?
20. Is there a way to have an X application draw inside a perl/Tk window?
21. Is there a version for Microsoft Windows(tm)?
22. Are there any international font packages for perl/Tk?
23. Are there any other ways to create event based interfaces from perl?
24. Where can I get more information on graphics (modules|scripts)?
25. Are there any major applications written in perl/Tk?
26. What is the history of pTk and perl/Tk?
27. What can we expect the future to hold?
28. How do I obtain the latest version of this FAQ?
29. Acknowledgements & maintainer.

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1. What is perl/Tk?

Perl/Tk (also known as pTk or ptk) is a collection of modules and code that attempts to wed the easily configured Tk 4 widget toolkit to the powerful lexigraphic, dynamic memory, I/O, and object-oriented capabilities of Perl 5. In other words, it is an interpreted scripting language for making widgets and programs with Graphical User Interfaces (GUI). (Examples of widget programs [not necessarily written in perl/Tk] include xterm, xclock, most web-browsers, etc.. They are programs with "GUI" interfaces of one sort or another and are subject to the effects of your window manager.)

The current release of Perl/Tk is based on "Tk 4.0p3" the widget Toolkit originally associated with the Tcl (Tool command language) scripting language. However, Perl/Tk does not require any of the lexical features/idiosynchrocies of Tcl. Perl/Tk uses perl 5 syntax, grammar, and data structures.

The ``Tk400.202'' package is the production release of perl/Tk (corresponding to Tcl/Tk-4.0p3) and was written primarily by Nick Ing-Simmons <Nick.Ing-Simmons@tiuk.ti.com> at Texas Instruments in Northampton, England, to work with the latest version of Larry Wall's ``perl''. Nick Ing-Simmons is currently busy converting the Tcl/Tk-4.1 code to perl callable code as well. An initial alpha release of the effort is available from CPAN as ``Tk402.000''.

The pTk code proper is an externally callable Tk toolkit (i.e. a re-write of the Tk 4.0 code that allows easier external linking & calling, especially by perl). Ptk can then be called from Perl 5 via the Tk.pm et al perl glue modules. Hence "ptk" does not necessarily refer to Perl Tk but could be taken to mean portable Tk - given a glue package to another language. The stated goal of the pTk code is to have its library usable from perl, Tcl, LISP, C++, python, etc.. It just so happens that present work is concentrating on perl.

Historical note: "ptk" was known as "ntk" before about 11:30 EST 4 May 1995.

The perl/Tk language is itself further extensible via the standard perl 5 module mechanism. A number of composite widget and special character extensions to the language have been written using perl modules.

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2. What is the difference between perl/Tk and Tkperl?

TkPerl was originally the name of a (now unsupported) perl 4 package that Malcolm Beattie <mbeattie@sable.ox.ac.uk> at Oxford University gave to his code to wed the Tk X toolkit with Perl. (He has since referred to that package as a different "kettle of fish" from perl/Tk.)

Since that beginning Malcolm has also come up with a Tcl module for perl 5 that has a Tcl::Tk module extension. That module allows the use of Tcl within a Perl script (i.e. you must know both languages to get your widgets to work.) If you are interested in that package instead, see the necessary kits for Malcolm Beattie's Tcl/Tk extensions to Perl, which have been distrubuted as Tcl-b#.tar.gz and TclTk-b#.tar.gz files in the authors/id/MICB/ directory at CPAN sites (locations given in a separate question in this FAQ).

The name "tkperl" is sometimes applied to the "perl/Tk" or "ptk" package that is the subject of this FAQ. Nick Ing-Simmons prefers "perl/Tk" as the name of the package, with "pTk" or "ptk" as contractions of that name as well as referring to something technically distinct: given the extensibility of the pTk code the "p" could also be taken to mean 'portable' or 'pure' (not to be confused with either the Helsinki University of Technology portTk, nor with Brian Warkentine's Rivet). In this document the code of interest is either referred to as "perl/Tk", "pTk", or "ptk" though the primary focus is on perl/Tk.

Warning: do not attempt to install both perl/Tk and Tcl/Tkperl in the same perl installation. The names in the respective modules overlap. In particular the Tcl::Tk module is declared in a Tk.pm file - so a statement like:

    use Tk;

A more extensive comparison of the differences between the Tkperl and the perl/Tk code is given in the Tcl-perl.pod file that is distributed with perl/Tk (see the following questions for locations).

Lastly, it should be mentioned that if you build your perl/Tk statically rather than dynamically it will make a new perl interpreter called tkperl (confusing isn't it? :-).

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3. Do I need Tcl/Tk in order to build Perl/Tk?

Short answer: No not at all. Perl/Tk is completely independent of Tcl/Tk.

Longer answer: In order to build Perl/Tk from source code you do need a recent version of perl, the perl/Tk source code kit, a graphical user interface library such as Xlib, a C or C++ compiler, and a make utility. In some rare cases Perl/Tk binaries are distributed for some platforms but that is more the exception than a general rule (see below).

If you will be attempting to port Perl/Tk to your platfrom then you might want to consult the document at:

    http://w4.lns.cornell.edu/~pvhp/ptk/ptkPORT.html

where each of these necessities is discussed in a bit more detail.

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4. Where is it?

Source code

(The rest of this question remains for historical reasons, as well as to point out some non CPAN resources.)

Tk-b8: The Tk-b8 kit remains on CPAN since it was compatible with the widely distributed and installed Perl (5.001m)

Binaries

Australia (please be patient and only try during off hours)
    ftp://syd.dit.csiro.au/pub/perl5/local/perl5.001m+Tk-b8-Linux-ELF.tar.gz

Binaries for the old Perl 5 & Tk-b6 are available for a number of UNIX platforms courtesy of Thomas Schlagel and Alan Stange of Brookhaven Lab at:

USA
    http://pubweb.bnl.gov/~ptk/

Physical media (mostly source code)

Walnut Creek Perl CD

This CD specifies a release date. $39.95

Cosmos Engineering Company

Offers Linux plus perl for sale on a 1 Gigabyte IDE hard drive for PC-like computers. $279.00 (Fall 1996)

Unix Review System Administration

A CD that contains "Perl 5.0" (and much other stuff including Tcl/Tk and Expect) for $49.95. Telephone: (800) 444-4881.

InfoMagic Mother of Perl

This 2 CD set contains perl 5.001 and sells for $35.00

Ready to Run

Perl (unknown version) available for sale for many types of Unix and other operating systems.

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5. What/Where is CPAN?

"CPAN" = Comprehensive Perl Archive Network a worldwide collection of anonymous ftp sites for Perl et al (not to be confused with CTAN which is for TeX, nor CSPAN which rarely deals with computer software). The files of particular interest to a perl/Tk programmer would include:

• The latest Tk release should be in the modules/by-authors/Nick_Ing-Simmons/ directory at any CPAN ftp site (listed below).
• The latest official Perl release should be in the src/ directory in a file called latest.tar.gz at any CPAN ftp site (listed below).
• If you need something older or newer than the "latest supported release" try the src/5.0/ directory at any CPAN ftp site (listed below).

• Alan Scheinine's SelFile.pm is in the modules/by-authors/Alan_Scheinine/ directory at any CPAN ftp site (listed below).
• Guy Decoux's BLT_Table geometry manager is in the modules/by-authors/id/GUYDX/ directory at any CPAN ftp site (listed below).
• Ilya Zakharevich's eText plug in replacement for the Text widget is in the modules/by-authors/id/ILYAZ/etext/ directory at any CPAN ftp site (listed below).
• Brent B. Powers' Tk-FileDialog and Tk-WaitBox are available from the modules/by-authors/id/BPOWERS/ directory at any CPAN ftp site (listed below).

• To run the ptknews script you will need Mail/Internet.pm from the Mailtools module kit, available from the modules/by-authors/id/GBARR/ directory at any CPAN ftp/http site (listed below). While there pick up the latest libnet-* module bundle too.
• The build of recent versions of perl/Tk requests that you have the URI::URL and HTML::Parse modules already installed. These modules are part of the libwww-perl-*.tar.gz kit, available from the modules/by-authors/id/GAAS/ at any CPAN ftp/http site (listed below).

• Assorted documentation for perl is in the doc/ directory at any CPAN ftp site (listed below).
• Fairly up-to-date versions of some Perl/Tk external documentation (such as this FAQ) is in the modules/by-authors/id/PVHP/ directory at any CPAN ftp/http site (listed below).
  (for Perl/Tk official documentation check the Tk/doc/*.htm files that are built with Nick's Tk kit on your computer.)

• Most things perl/Tk (with certain exceptions) are also linked to a modules/by-module/Tk/ directory at any CPAN ftp/http site (listed below).
• The long version of Tim Bunce and Andreas Koenig's module list helps you sort out things like "which kit is HTML::Parse a part of?". It is in modules/00modlist.long.html and is also posted periodically to newsgroups.

Updated: Sun Dec 8 17:12:55 EST 1996

Africa
  South Africa    
    ftp://ftp.is.co.za/programming/perl/CPAN/           196.4.160.12
Asia
  Hong Kong       
    ftp://ftp.hkstar.com/pub/CPAN/                      202.82.7.4
  Japan           
    ftp://ftp.jaist.ac.jp/pub/lang/perl/CPAN/           150.65.7.5
    ftp://ftp.lab.kdd.co.jp/lang/perl/CPAN/             192.26.91.6
  South Korea     
    ftp://ftp.nuri.net/pub/CPAN/                        203.255.112.6
  Taiwan          
    ftp://dongpo.math.ncu.edu.tw/perl/CPAN/             140.115.25.3
Australasia
  Australia       
    ftp://coombs.anu.edu.au/pub/perl/CPAN/              150.203.76.2
    ftp://ftp.mame.mu.oz.au/pub/perl/CPAN/              128.250.209.2
  New Zealand     
    ftp://ftp.tekotago.ac.nz/pub/perl/CPAN/             202.49.6.24
Europe
  Austria         
    ftp://ftp.tuwien.ac.at/pub/languages/perl/CPAN/     128.130.34.160
  Belgium         
    ftp://ftp.kulnet.kuleuven.ac.be/pub/mirror/CPAN/    134.58.127.2
  Czech Republic  
    ftp://sunsite.mff.cuni.cz/Languages/Perl/CPAN/      194.50.23.220
  Denmark         
    ftp://sunsite.auc.dk/pub/languages/perl/CPAN/       130.225.51.30
  Finland         
    ftp://ftp.funet.fi/pub/languages/perl/CPAN/         128.214.248.6
  France          
    ftp://ftp.pasteur.fr/pub/computing/unix/perl/CPAN/  157.99.64.12
  Germany         
    ftp://ftp.leo.org/pub/comp/programming/languages/perl/CPAN/  131.159.0.252
    ftp://ftp.rz.ruhr-uni-bochum.de/pub/CPAN/           134.147.32.42
    ftp://ftp.uni-hamburg.de/pub/soft/lang/perl/CPAN/   134.100.32.54
  Greece          
    ftp://ftp.ntua.gr/pub/lang/perl/                    
  Hungary         
    ftp://ftp.kfki.hu/pub/packages/perl/CPAN/           148.6.0.5
  Italy           
    ftp://cis.utovrm.it/CPAN/                           160.80.22.17
  the Netherlands 
    ftp://ftp.cs.ruu.nl/pub/PERL/CPAN/                  131.211.80.17
    ftp://ftp.EU.net/packages/cpan/                     134.222.91.7
  Norway          
    ftp://ftp.uit.no/pub/languages/perl/cpan/           129.242.4.34
  Poland          
    ftp://ftp.pk.edu.pl/pub/lang/perl/CPAN/             149.156.132.152
    ftp://sunsite.icm.edu.pl/pub/CPAN/                  148.81.209.3
  Portugal        
    ftp://ftp.ci.uminho.pt/pub/lang/perl/               193.136.16.247
    ftp://ftp.telepac.pt/pub/CPAN/                      194.65.5.98
  Russia          
    ftp://ftp.sai.msu.su/pub/lang/perl/CPAN/            158.250.29.1
  Slovenia        
    ftp://ftp.arnes.si/software/perl/CPAN/              193.2.1.72
  Spain           
    ftp://ftp.etse.urv.es/pub/mirror/perl/              193.144.20.6
    ftp://ftp.rediris.es/mirror/CPAN/                   130.206.1.2
  Sweden          
    ftp://ftp.sunet.se/pub/lang/perl/CPAN/              130.238.253.4
  Switzerland     
    ftp://sunsite.cnlab-switch.ch/mirror/CPAN/          193.5.24.1
  UK              
    ftp://ftp.demon.co.uk/pub/mirrors/perl/CPAN/        158.152.1.44
    ftp://sunsite.doc.ic.ac.uk/packages/CPAN/           193.63.255.1
    ftp://unix.hensa.ac.uk/mirrors/perl-CPAN/           129.12.200.129
North America
  Ontario         
    ftp://ftp.utilis.com/public/CPAN/                   207.34.209.49
    ftp://enterprise.ic.gc.ca/pub/perl/CPAN/            192.197.182.100
  California      
    ftp://ftp.digital.com/pub/plan/perl/CPAN/           204.123.2.4
    ftp://ftp.cdrom.com/pub/perl/CPAN/                  165.113.58.253
  Colorado        
    ftp://ftp.cs.colorado.edu/pub/perl/CPAN/            128.138.243.20
  Florida         
    ftp://ftp.cis.ufl.edu/pub/perl/CPAN/                128.227.205.206
  Illinois        
    ftp://uiarchive.cso.uiuc.edu/pub/lang/perl/CPAN/    128.174.5.14
  Massachusetts   
    ftp://ftp.iguide.com/pub/mirrors/packages/perl/CPAN/  206.15.105.99
  New York        
    ftp://ftp.rge.com/pub/languages/perl/               157.225.178.12
  North Carolina  
    ftp://ftp.duke.edu/pub/perl/                        152.3.233.7
  Oklahoma        
    ftp://ftp.ou.edu/mirrors/CPAN/                      129.15.2.40
  Oregon          
    ftp://ftp.orst.edu/pub/packages/CPAN/               128.193.4.12
  Texas           
    ftp://ftp.sedl.org/pub/mirrors/CPAN/                198.213.9.194
    ftp://ftp.metronet.com/pub/perl/                    192.245.137.6
South America
  Chile           
    ftp://sunsite.dcc.uchile.cl/pub/Lang/perl/CPAN/     146.83.5.204

    http://perl.com/cgi-bin/cpan_mod?module=Tk
    http://perl.com/cgi-bin/cpan_mod?module=Tk&readme=1

    ftp> get Tk400.202.tar.gz Tk400.202.tar

    perl -MCPAN -e 'install "Tk"'

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6. How do I build it?

In general, building perl/Tk requires:

1. A made & installed perl (requires a C language compiler). You may need different versions of perl depending on which version of Tk you wish to run.
2. A C language compiler for the Tk code itself.
3. A linkable Xlib (.o, .so, .a, etc.) for X-windows.

Step - by - step the commands to build the Tk extension to Perl are (for the dynamically linked version) roughly as follows:

1. make install # the appropriate version of perl.
2. uninstall # prior versions of the Tk extension to perl.
3. gunzip -c Tk400.202.tar.gz | tar xvf - (options to tar may vary esp. on SysV)
4. cd Tk400.200
5. read INSTALL
6. perl Makefile.PL
7. make
8. make test
9. make install

Note carefully that this process leaves behind a large amount of documentation and examples in various sub-directories. You are strongly encouraged to look carefully through your build tree for docs, examples, etc. and keep those valuable files in a safe place. You might consider tar-ing them off and installing in a webserver directory tree.

A relatively easy way to determine if the perl on your system allows for dynamic linking was mentioned by Kenneth Albanowski <kjahds@kjahds.com>. If the following does not say "dl_none.xs" then you probably do have dynamically linked perl (or perhaps a very non-Unixy perl):

    perl -e 'use Config; print $Config{dlsrc},"\n"'

Here is a little more detailed discussion of each the steps just given:

• Install Perl Read the Tk files (Tk*/README, etc.) for info on which version of perl is required for the perl/Tk kit you obtained.) For code locations see a CPAN site (separate question in this FAQ), the actual installation instructions come bundled in the perl***.tar.gz distribution file. (Perl Configure & make troubles are beyond the scope of this FAQ - please see the Perl FAQ itself or the INSTALL file for more help with this critical step.)
  You can install perl almost anywhere you like by specifying the -Dprefix=/path argument to sh Configure
• Unpack perl/Tk outside the Perl distribution
  (i.e. outside the perl build, perl install, or perl lib areas).
  gunzip Tk400.202.tar.gz
  tar -xvf Tk400.202.tar
  (Your tar program may not take -xvf. The resultant Tk400.202/ area will be referred to as your ``Tk build'' directory throughout this document.)
  
• Read INSTALL carefully
  cd Tk400.202
  pager INSTALL
  where pager is the program you use to scroll through text files more or less. Be sure to read it and don't just pound away on the spacebar.
• If necessary remove any previously installed version of perl/Tk
  If you had a previously working version of Tk installed, you may need to resurrect the Makefile for it and execute:
  make uninstall
  make realclean
  before you unpack the new version. (The uninstall target of MakeMaker is relatively new so please be careful here.)
  
• Have perl generate a custom Makefile.
  perl Makefile.PL
  (see below for more on this step.)
  
• Compile.
  make
  (if and only if building static: make tkperl
  
• Test.
  make test
  
• Install.
  make install
• Play with it.
  basic_demo
  (modify #! line if necessary, or specify /path/to/perl ./basic_demo)
  (warning if you build Tk-b9.01 with perl5.002gamma then change the line in basic_demo from
  use lib ./blib;
  to
  use lib qw(blib/arch blib/lib);)
• Save the documentation and examples in a safe accessible place.
  use tar, cp, mv, chmod or whatever you prefer to save the valuable ancillary files from your Tk build tree.
  

    perl Makefile.PL X11=/usr/local/X11R5

    perl Makefile.PL X11INC=/usr/local/share/X11R5/include \
                     X11LIB=/usr/local/arch/X11R5/lib

If you still run into trouble take a look at the INSTALL, the README and the README file for your specific system (e.g. README.AIX, README.OSF, etc.). You might also find your system mentioned in the ptk hyper-mail archive at:

    http://www.rosat.mpe-garching.mpg.de/mailing-lists/ptk/
or
    http://pubweb.bnl.gov/~ptk/
or
    ftp://ftp.ccd.bnl.gov/pub/ptk/archives/

    http://www.rosat.mpe-garching.mpg.de/mailing-lists/Perl5-Porters/
    http://www.hut.fi/~jhi/perl5-porters.html

Presented here are the beginnings of a list of problems associated with building perl/Tk on various platforms (for help building perl itself please refer to the Perl FAQ). This list is in no way complete nor authoritative (nor is it necessarily even up-to-date!) but simply lists problems people have reported. Keep in mind that your installation may differ (e.g. location differences such as /usr/bin/perl vs. /usr/local/bin/perl) even if its the same platform listed here:

A Sampling of Perl/Tk Platforms:

AIX:

As of perl5.002b & Tk-b9.01 README.AIX says no patching is necessary.

For Tk-b8: modifying the perl.exp file may be necessary. There is a patch in Tk-b8/README.AIX. It may be necessary to make regen_headers after the patch.

FreeBSD:

Nate Patwardhan <nvp@nfic.com> reports no trouble at all with Tk400.200 on FreeBSD-2.1.5 or FreeBSD-2.2.1.

HPUX:

For Tk-b11: One person reports a need to add #define TIMEOFDAY_TZ to the tkConfig.h header file in order to compile on HPUX 9.05.

Previous versions: Most people seem to prefer the dynamic linking afforded by a recent version of the gcc compiler on this system.

Linux:

John C. Wingenbach indicates that should you encounter an error message like Cannot find -lX11 anywhere at ./myConfig line 184 when running your perl Makefile.PL (under Slakware 3.0) that you should be more specific about -l/path/to/libX11.a.
Adam Wasserman <awasser@hermes.sgc.com> has graciously provided a compilation of Linux compilation trials & tribulations. It is an (as yet un-edited) document available at: http://w4.lns.cornell.edu/~pvhp/ptk/hints/linux_compile.txt

MachTen:

Mark Pease <pease@act.sps.mot.com> mentions that:
I was able to get Tk-b11.02 running under MachTen 2.2 perl5.002_01. I did need to make one change to get a round a MachTen problem. In pTk/tclUnix.h, pwd.h is included, but it is also included in pTk/tkPort.h (which is included in Lang.h, which is use by tclUnixUtil.c, whew!)

MachTen's pwd.h can't be included more that once or you get an error.

It looked to me like tclUnix.h was only used in tclUnixUtil.c, so I commented out the #include <pwd.h> in tclUnix.h.

NetBSD:

Jesus M. Gonzalez <jgb@gsyc.inf.uc3m.es> mentions success with:
Tk-b11.01 compiles, installs and runs just out of the box in NetBSD-1.1/i386. I just followed the INSTALL instructions.

NeXTSTEP:

Gerd Knops recently posted a discussion of the steps to get perl running on several NeXTSTEPs to p5p.

OS/2:

Ilya Zakharevich <ilya@math.ohio-state.edu> has compiled a modified form of Tk-b11.02 to work with the Xfree86 client/server package, as well more advanced versions working with the Open32 PM package.

OSF/1:

As of perl5.002b & Tk-b9.01 you will probably be able to follow the usual instructions. John Stoffel <john@wpi.edu> reports that if you use gcc (rather than cc) you should use at least version 2.7.2

For Tk-b8: make is reputedly not up to the task on this system. Tk-b8/README.OSF recommends gmake instead.
Stephane Bortzmeyer <bortzmeyer@pasteur.fr> reports a successful build with Perl 5.001m, xsubpp 1.922, MakeMaker 4.23. He points out that it was necessary for him to upgrade the xsubpp and MakeMaker that he received with his copy of Perl5.001m.

SCO:

For Tk-b8: Eric J. Bohm <bohm@cs.Buffalo.EDU> reported a need to comment out line(s) from myConfig and GNUMakefiles using GNU make 3.67. (See Tk-b8/README.SCO for specifics.)

SGI (Irix):

For Tk-b11.02: Phillip Moore <wpm@morgan.com> reports a clean build on IRIX 5.3.

Matthew Black <black@csulb.edu> recently mentioned a need to apply "patchSG0000596" to get perl sockets to work. His message was copyrighted and is not included here. Send e-mail to him to find out where the get "patchSG0000596".

Suns:

SunOS (BSD):
For Tk-b10 on SunOS 4.1.3_U1
using SparcWorks acc 3.0.1 Frederick L. Wagner <derf@ti.com> reports needing to use the perl malloc rather than the system malloc() when building perl.
For Tk-b8: Tom Tignor <tpt2@BBN.COM> reports the following on SunOS (sun4m sparc): Tue, 28 Nov 1995 13:19:42
In trying to make, I got a "write: argument mismatch" error for the file ptK/Lang.h. I looked at the file and found the offending function, Tcl_GetOpenFile, which has a third argument called "doWrite" (not "write") in tkGlue.c. I changed the argument from "write" to "doWrite" in Lang.h and it's compiling fine (for the moment. :)
Solaris (System V):
For Tk-b8: There is trouble getting perl to use Socket routines (i.e. trouble with make perl itself not necessarily trouble with Tk-b8). See the perl FAQ for more info or the .shar file that Tom Christiansen occasionally posts to comp.lang.perl.misc. Further information on perl inter process communication can be found in the perlipc* files at: ftp://ftp.perl.com/perl/info/everything_to_know/.

SVR4:

For Tk-b8: Martha G. Armour and Len Reed report on two separate hardware platforms running SVR4 - extensive details in Tk-b8/README.SVR4. Interestingly, they report no trouble at all on Linux.

Ultrix:

Peter Prymmer reports that with Tk-b11 it was necessary to change the line in Makefile.PL that reads:
'LIBS' => ["$xlib -lX11 -lpt -lsocket -lnsl -lm"],
to read:
'LIBS' => ["$xlib -lX11 -lpt -lsocket -lnsl -lm -ldnet"],
because of a newer X11 in /usr/local that needed the DECnet protocol linking.

John Stoffel reports a successful build of static Tk-b10 on Ultrix 4.5.

Windows NT:

Nick Ing-Simmons reports success with the alpha Tk404.000 kit, perl5.004, and Visual C++.

non-Unix(ish)es:

    http://www.rosat.mpe-garching.mpg.de/mailing-lists/Perl5-Porters/
    http://www.hut.fi/~jhi/perl5-porters.html

    http://w4.lns.cornell.edu/~pvhp/ptk/ptkPORT.html

Return to table of contents

7. Where is the Documentation?

A great deal of Perl/Tk documentation gets installed as part of the Tk extension building process. Hence, a great deal of documentation is probably residing on your computer already.

More documentation is "in the works": there are several books dealing with perl/Tk in progress, an ongoing magazine column and a growing FAQ (the document you are presently reading).

The additional material you may want to look at can be split into Perl/Tk, Perl, Tcl/Tk, and X documentation categories:

Perl/Tk Specific Documentation

The man pages

In your Tk build directory there should be a doc/ sub-directory in which there are a number of .htm files (after you make install). These files were originally Tcl/Tk man pages (from the man* sub-directories), but the *.htm files have been converted to Perl syntax and rendered in HTML format. You can use the Perl/Tk web browser to view them locally with a command like:

    tkweb index.html

    http://w4.lns.cornell.edu/~pvhp/ptk/doc/

The newsgroup

The nTk/pTk mailing list

The nTk/pTk Mailing List Archive is a very useful source of information too, and is accesible at either

    http://pubweb.bnl.gov/~ptk/

    ftp://ftp.ccd.bnl.gov/pub/ptk/archives/

    http://www.rosat.mpe-garching.mpg.de/mailing-lists/ptk/

    subscribe ptk joe.user@somewhere (Joe D. User)

To send a message to all recipients of the mailing list send e-mail to <ptk@lists.stanford.edu>.

To remove yourself from the mailing list send e-mail to majordomo@lists.stanford.edu (i.e. <majordomo@lists.stanford.edu>) with the following command in the body of your e-mail message:

    unsubscribe ptk joe.user@somewhere (Joe D. User)

(Please note: one does not send unsubscribe messages to the ptk list. One does send "unsubscribe ptk" messages to a special e-mail list administration program. In the case of the ptk list you send to majordomo@lists.stanford.edu. You must of course do this from the account and computer from which you initially subscribed. In particular if you are viewing the hypertext version of this FAQ you may not be able to unsubscribe from majordomo@lists.stanford.edu by following the mailto: hyperlinks - if your web-browser account/computer is different from your subscribe to e-mail-lists account/computer (the details of this might depend on which browser you use though). Thank you for your cooperation on this.)

The demo programs

• or perl5/site_perl/Tk/demos/ or perl5/site_perl/Tk/demos/widget_lib/ directories (recent Tk's).
• Tk#/ or perl5/Tk/demos/ or perl5/Tk/demos/widget_lib/ directories (older versions e.g. Tk-b8).

In order to determine where on your system the perl5/ directory is located type the following one-line perl command (at your shell prompt - this is not a line from a perl script):

    perl -e 'print join("\n",@INC,"");'

More on the pod & man documentation

The raw pod files that come with the Tk kit are examples of the perl "plain old documentation" format and are just about human readable as they are (e.g. you may more, cat, or less them; or send them to a printer). Many (not all) of the perl/Tk pod documents get are converted to *roff format and are installed in you perl man page area as part of the perl/Tk build process.

If you have a recent version of perl/Tk try something like man 3 Tk::Tk. If this does not work check your manual page path with

    perl -MConfig -e 'print $Config{man1dir},"\n",$Config{man3dir},"\n"'

"Raw" .pod (such as UserGuide.pod) can be viewed with the tkpod hypertext pod viewer. Raw .pod may also be run through any one or more of a large numbers of re-formatting perl filters. Such programs include pod2man, pod2text, pod2html, pod2latex, etc. (these get installed when you install perl). Other translators pod2texinfo, pod2fm, pod2pdf, etc., also exist. Check a CPAN site for these scripts if you do not already have them.

A command line like the following (but subject to local variations) should work for you:

    tkpod site_perl/Tk/UserGuide.pod

    pod2man perl5/Tk/UserGuide.pod | nroff -man | more

    pod2man UserGuide.pod | nroff -man | more

    perldoc UserGuide

    tkpod ColorEditor.pm

If you have misplaced your tkpod program but still want that GUI look and feel (like xman) make the appropriate changes to the following script:

    #!/usr/bin/perl
    use Tk;
    use Tk::Pod;
    my $m = new MainWindow;
    $m -> Pod(-file => 'ColorEditor.pm');
    # or use command line path/filename:
    # $m -> Pod(-file => $ARGV[0]);
    MainLoop;

A miscellany of internet perl/Tk resources includes:

World Wide Web - perl/Tk man pages
    http://pubweb.bnl.gov/~ptk/doc/index.html
    http://w4.lns.cornell.edu/~pvhp/ptk/doc/
    http://w4.lns.cornell.edu/~pvhp/ptk/pod/
The Perl/Tk Newsgroup
    comp.lang.perl.tk
Perl Newsgroups
    comp.lang.perl.misc
    comp.lang.perl.anounce
    comp.lang.perl.modules
Tcl Newsgroups
    comp.lang.tcl
    comp.lang.tcl.announce
Miscellaneous Newsgroups
    comp.answers
    news.answers
Perl/Tk FAQ-Archives (ftp sites) [Note: FAQ may be many separate files]
 (see also CPAN sites)
    ftp://rtfm.mit.edu/pub/usenet/comp.lang.perl.tk
    ftp://rtfm.mit.edu/pub/usenet-by-hierarchy/comp/lang/perl/tk
    ftp://ftp.uu.net/usenet/news.answers/perl-faq/ptk-faq
    ftp://ftp.ccd.bnl.gov/pub/ptk/                   130.199.54.188
    ftp://ftp.ccd.bnl.gov/pub/ptk/ptkFAQ.txt         130.199.54.188
    ftp://ftp.wpi.edu/perl5/pTk-FAQ                  130.215.24.209
    ftp://perl.com/pub/perl/doc/ptkFAQ.gz            199.45.129.30
    ftp://perl.com/pub/perl/doc/ptkFAQ.ps.gz         199.45.129.30
WWW-FAQ for perl/Tk
    http://w4.lns.cornell.edu/~pvhp/ptk/ptkTOC.html
    http://w4.lns.cornell.edu/~pvhp/ptk/ptkFAQ.html
World Wide Web - perl/Tk info sites
    http://pubweb.bnl.gov/~ptk/
    http://fxfx.com/kgr/compound/ (Perl Tk Compound Widget Page)
    http://w4.lns.cornell.edu/~pvhp/ptk/ptkIMG.html (FAQ image supplement)
    http://w4.lns.cornell.edu/~pvhp/ptk/etc/
    http://w4.lns.cornell.edu/~pvhp/ptk/misc/
    http://w4.lns.cornell.edu/~pvhp/ptk/PNMTYAK/
    http://www.mirai.com/wks/
The Mailing list
    majordomo@lists.stanford.edu 
    ptk@lists.stanford.edu 

Perl Specific Documentation

    http://www.perl.com/perl/info/books.html

Programming Perl 2nd Edition
Larry Wall, Tom Christiansen, & Randal L. Schwartz with Stephen Potter
(c) 1996 O'Reilly & Associates Inc.
ISBN 1-56592-149-6 (English)

Learning Perl, 2ndEdition
Randal L. Schwartz
June 1997 (est.) O'Reilly & Associates Inc.
ISBN 1-56592-284-0 (English)

Learning Perl (The Llama)
Randal L. Schwartz
Copyright (c) 1993 O'Reilly & Associates Inc.
ISBN 1-56592-042-2 (English)
ISBN 2-84177-005-2 (French)
ISBN 3-930673-08-8 (German)
ISBN 4-89502-678-1 (Japanese)

Programming Perl (The Camel)
Larry Wall and Randal L. Schwartz
Copyright (c) 1991 O'Reilly & Associates Inc.
ISBN 0-937175-64-1 (English)
ISBN 3-446-17257-2 (German) (Programmieren in Perl, translator: Hanser Verlag)
ISBN 4-89052-384-7 (Japanese)

    http://www.metronet.com/1h/perlinfo/perl5/

Perl 5 Interactive Course
Jon Orwant
(c) 1996 The Waite Group Press
A Division of SAMS Publishing, Corte Madera, CA USA
ISBN: 1-57169-064-6

    http://www.xs4all.nl/~jvromans/perlref.html

Perl 5 Desktop Reference
Johan Vromans
Copyright (c) February 1996 O'Reilly & Associates Inc.
ISBN: 1-56592-187-9; Order number: 1879

Eric F. Johnson has a book that discusses many perl5 for Unix vs. perl5 for Windows NT issues. He includes a final chapter with extensive discussion of the Tk extension and the ->Text() widget in particular. The information on that book is:

Cross-Platform Perl
(c) 1996 Eric F. Johnson
MIS:Press/M&T Books
ISBN: 1-55851-483-X

Kamran Husain and Robert F. Breedlove have written a perl 5 book that includes a chapter on Tk with some discussion of Menu()s. That book is:

Perl 5 Unleashed
Kamran Husain and Robert F. Breedlove
(c) 1996 Sams Publishing, Indianapolis, IN
ISBN: 0-672-30891-6

There is also a "Perl 5 How-To" book available that contains a great deal of erroneous information about perl/Tk. Among other things that book wrongly mentions that it is necessary to have a complete Tcl/Tk library installed on one's system to compile the Tk extension to perl. (They are incorrect - it is only necessary to have the appropriate perl version, libc and Xlib, the Tk extension is otherwise "self-contained").

There is also a book on perl web client. It features a a chapter on perl/Tk that was written by Nancy Walsh:

Web Client Programming with Perl
Clinton Wong
1st Edition March 1997
O'Reilly & Associates Inc.
ISBN: 1-56592-214-X; Order number: 214X

Additional book information may be found at Tom Christiansen's perl & cgi books page, or at his Perl-related Book Reviews page.

The multi-part perl 5 manual pages are available (assuming they have been installed in your MANPATH, type man perl, man perlmod etc.).

The perl 5 man pages are also available on the web at a number of locations. In general the more recent the documentation the more helpful it is.

In addition to the CPAN ftp source sites, a miscellany of internet perl resources includes:

Newsgroups
    comp.lang.perl.misc
    comp.lang.perl.announce
    comp.lang.perl.modules
    comp.infosystems.www.authoring.cgi
    comp.answers
    news.answers
Perl FAQ-Archives (ftp sites) [Note: FAQ may be many separate files]
(as of 5.004 the FAQ ships in pod format with perl)
    (see also the CPAN sites)
  North America
    ftp://rtfm.mit.edu/pub/usenet/news.answers/perl-faq/
    ftp://ftp.uu.net/usenet/news.answers/perl-faq  192.48.96.9
    ftp://ftp.khoros.unm.edu/pub/perl/faq.gz       198.59.155.28
  Europe 
    ftp://ftp.cs.ruu.nl/pub/NEWS.ANSWERS/perl-faq/ 131.211.80.17
    ftp://src.doc.ic.ac.uk/packages/perl/FAQ       146.169.2.10
Gopher Perl FAQ 
    gopher://gopher.metronet.com/11/perlinfo/faq
WWW-FAQ for Perl
    http://www.perl.com/perl/faq/
    http://www.smartpages.com/bngfaqs/comp/lang/perl/top.html
    http://www.smartpages.com/bngfaqs/comp/lang/perl/misc/top.html
    http://www.smartpages.com/bngfaqs/comp/lang/perl/announce/top.html
    http://www.cis.ohio-state.edu/hypertext/faq/usenet/perl-faq/top.html
Perl for Win32 FAQ  (discusses Win95)
    http://www.perl.org/CPAN/doc/FAQs/win32/Perl_for_Win32_FAQ.html

Perl info sites
Gopher (gopher:70) perl info sites
  USA
    gopher://gopher.metronet.com/11h/perlinfo
World Wide Web (http:80) perl info sites
  USA
    http://www.yahoo.com/Computers_and_Internet/Languages/Perl/index.html
    http://www.perl.com/
    http://www.khoros.unm.edu/staff/neilb/perl/home.html
    http://www.khoros.unm.edu:80/staff/neilb/perl/metaFAQ/
    http://www.metronet.com/perlinfo/
    http://www.metronet.com/perlinfo/perl5.html (Perl 5)
    http://www.eecs.nwu.edu/perl/perl.html
    http://cesr39.lns.cornell.edu/public/perl/
    http://www.virtualschool.edu/mon/Perl.html
    http://www.hermetica.com/technologia/unexec/
    http://www.oac.uci.edu/indiv/ehood/perlWWW/
    http://web.sau.edu/~mkruse/www/scripts/
    http://orwant.www.media.mit.edu/the_perl_journal/
    http://www.perl.com/Architext/AT-allperl.html
    http://www.mispress.com/introcgi/
    http://www.walrus.com/~smithj/webcan/
    http://web.syr.edu/~chsiao05/cps600_project.html
    http://www.iftech.com/classes/webdev/webdev_perl.htm
    http://www.cc.iastate.edu/perlmenu/
    http://www.ora.com/www/item/cgi_prog.html
  UK
    http://pubweb.nexor.co.uk/public/perl/perl.html
    http://www.bio.cam.ac.uk/web/form.html
Web references to Perl mailing lists
    http://www.perl.com/perl/info/mailing-lists.html
    http://www.nicoh.com/cgi-bin/lwgate/PERL5-PORTERS/
    http://www.hut.fi/~jhi/perl5-porters.html
    http://www.rosat.mpe-garching.mpg.de/mailing-lists/

Tcl/Tk Specific Documentation

Tcl and the Tk Toolkit
John K. Ousterhout
Copyright (c) 1994 Addison-Wesley Publishing Company
ISBN 0-201-63337-X (alk. paper)
LOC QA76.73.T44097 1994; 005.13'3--dc20

Practical Programming in Tcl and Tk
Brent Welch
Copyright (c) 1995 Prentice Hall
ISBN 0-13-182007-9

Within the tclsh or wish shells your manpath includes the tcl/tk man pages (which may not be in your login MANPATH). Thus from the % prompt within either shell type commands like:

    % man -k Tk

The Tcl/Tk Reference Guide is also a source of useful information. Although it's Tcl specific most perl/Tk commands can be, more or less, easily derived from it. [Note that in perl/Tk the names of some functions and some configuration options have changed slightly from their Tcl/Tk counterparts. With recent versions of perl/Tk a great many functions start with an upper case letter and continue with all lower case letters (e.g. there is a perl/Tk Entry widget but no entry widget), and many configuration options are all lower case (e.g. there is a perl/Tk highlightthickness option but no highlightThickness option).] You may fetch the Tcl/Tk Reference Guide (may require LaTeX for installation) from:

  ftp://ftp.slac.stanford.edu/software/TkMail/tkref-4.0.1.tar.gz 134.79.18.30
  ftp://ftp.aud.alcatel.com/tcl/docs/tkref-4.0.1.tar.gz          198.64.191.10

Newsgroups
    comp.lang.tcl
    comp.lang.tcl.announce
    comp.infosystems.www.authoring.cgi
    comp.answers
    news.answers
FAQ-Archive (ftp) [Note: Tcl FAQ may be many files, Tk FAQ is one file]
    ftp://ftp.aud.alcatel.com/tcl/docs/                          198.64.191.10
    ftp://rtfm.mit.edu/pub/usenet/news.answers/tcl-faq
    ftp://rtfm.mit.edu/pub/usenet/news.answers/tcl-faq/tk
WWW-FAQ for Tcl/Tk
    http://www.teraform.com/%7Elvirden/tcl-faq/
    http://www.smartpages.com/faqs/tcl-faq/top.html
    http://www.smartpages.com/bngfaqs/comp/lang/tcl/top.html
    http://www.cis.ohio-state.edu/hypertext/faq/usenet/tcl-faq/top.html
  http://www.cis.ohio-state.edu/hypertext/faq/bngusenet/comp/lang/tcl/top.html
    http://www.sco.com/Technology/tcl/Tcl.html
World Wide Web - Tcl/Tk info sites
  Canada
    http://web.cs.ualberta.ca/~wade/Auto/Tcl.html
  UK
    http://http2.brunel.ac.uk:8080/~csstddm/TCL2/TCL2.html
    http://www.cis.rl.ac.uk/proj/TclTk/
  USA
    http://www.yahoo.com/Computers_and_Internet/Languages/Tcl_Tk/index.html
    http://www.sunlabs.com/research/tcl/docs.html
    http://www.sunlabs.com/research/tcl/4.0.html
    http://www.sco.com/Technology/tcl/Tcl.html
    http://www.neosoft.com/tcl/
    http://www.elf.org/tcltk-man-html/contents.html
Tcl/Tk - miscellaneous extensions
    ftp://ftp.cme.nist.gov/pub/expect/
    http://www.cs.hut.fi/~kjk/porttk.html
    http://www.cis.upenn.edu/~ioi/tix/tix.html
    http://www.ece.cmu.edu/afs/ece/usr/svoboda/www/th/homepage.html
    http://www.tcltk.com/ [incr Tcl]
    http://www.neosoft.com/tcl/TclX.html
    http://www.eolas.com/eolas/webrouse/tcl.htm [WebWish]
    http://www.se.cuhk.hk/~hkng2/big5tk/big5tk.html
    http://www.cs.uoregon.edu/~jhobbs/work/ [BLT etc.]

X Documentation

There are a number of X resources on the internet including:

Newsgroups
    comp.windows.x
    comp.windows.x.announce
    comp.windows.x.apps
X FAQs:
    ftp://ftp.x.org/contrib/faqs/
X FAQ on the World Wide Web:
    http://www.x.org/ftp/contrib/faqs/x-faq-multipart/x-faq-1
    http://www.x.org/ftp/contrib/faqs/x-faq-multipart/x-faq-2
    http://www.x.org/ftp/contrib/faqs/x-faq-multipart/x-faq-3
    http://www.x.org/ftp/contrib/faqs/x-faq-multipart/x-faq-4
    http://www.x.org/ftp/contrib/faqs/x-faq-multipart/x-faq-5
    http://www.x.org/ftp/contrib/faqs/x-faq-multipart/x-faq-6
    http://www.x.org/ftp/contrib/faqs/x-faq-multipart/x-faq-7
X Window System book info on the Web:
    http://www.x.org/ftp/contrib/docs/Xbibliography.OReilly
    http://www.ora.com/catalog/v1/
    http://www.ora.com/catalog/v2/
    http://www.ora.com/catalog/v3/
    http://www.ora.com/catalog/v4/
    http://www.ora.com/catalog/v5/
    http://www.ora.com/catalog/v6a/
    http://www.ora.com/catalog/v6b/
    http://www.ora.com/catalog/v6c/
    http://www.ora.com/catalog/r6/noframes.html
    http://www.ora.com/oracom/prog/flanart.html
World Wide Web - X Window System info sites
    http://www.x.org/
    http://www.x.org/consortium/GettingX.html
    http://www.x.org/consortium/x_info.html
    http://www.x.org/consortium/R6.1doc/man/X11/
    http://www.wolfram.com/~cwikla/widget/
    http://www.zeta.org.au/~rosko/pigui.htm
    http://www.rahul.net/kenton/xsites.html
    http://www.unx.com/DD/txaCurrent.shtml

Return to table of contents

8. How do I write scripts in perl/Tk?

Start your script as you would any perl script (e.g. #!/usr/bin/perl, #!/usr/local/bin/perl, #!/opt/bin/perl, [built static? then #!/usr/bin/tkperl], whatever, see the perlrun(1) man page for more information).
Throwing the -w warning switch is recommended.
The use of the statement use strict; is recommended.
Use of the statement use Tk; is required.

A simple "Hello World!" widget script could be written as follows:

    #!/usr/local/bin/perl -w

    use strict;
    use Tk;

    my $main = new MainWindow;
    $main->Label(-text => 'Hello World!'
                 )->pack;
    $main->Button(-text => 'Quit',
                  -command => sub{exit}
                  )->pack;
    MainLoop;

Note the use of the -> infix dereference operator. Most things in calls to perl/Tk routines are passed by reference.

Note also the use of the => operator which is simply a synonym for the comma operator (well it is a bit more than that :-). In other words, the arguments that get passed to Label and Button in the above example are good old perl associative arrays (perl 5 people prefer to call them "hashes" however). Indeed, we might have written the above as:

    #!/usr/local/bin/perl -w

    use strict;
    use Tk;

    my $main = new MainWindow;
    $main->Label(-text , 'Hello World!'
                 )->pack;
    $main->Button(-text , 'Quit',
                  -command , sub{exit}
                  )->pack;
    MainLoop;

    #!/usr/local/bin/perl -w
    use strict;
    use Tk;
    my $main = new MainWindow;

    my %hello = ('-text','Hello World!');
    my %quit_com = ('-text' => 'Quit', '-command' => sub{exit});

    $main->Label(%hello)->pack;
    $main->Button(%quit_com)->pack;
    MainLoop;

Lastly, we note the extensive use of the my function in most perl/Tk programs. my is roughly equivalent to local in Perl 4 - but is purported to be "faster and safer" as well as much more strictly local in scope. See perlfunc(1) manpage for more information on my.

Other examples of code may be found in the perl5/Tk/demos/ directory and in perl5/Tk/demos/widget_lib/.

(A variant on this scipt called hello is available in the file perl5/Tk/demos/hello in your own pTk distribution. Also, Source code for this and other examples from UserGuide.pod may be found at http://w4.lns.cornell.edu/~pvhp/ptk/pod/. To load code from the web save as a local filename, edit the first line to point to your perl interpreter, then: chmod u+x filename, then execute: filename.)

Return to table of contents

9. What widget types are available under perl/Tk?

The following Tk widget primitives are available under perl/Tk:

• Button
• Canvas
• Checkbutton
• Entry
• Frame
• Label
• Listbox
• Menu
• Menubutton
• Message
• Radiobutton
• Scale
• Scrollbar
• Text
• Toplevel

• HList
• InputOnly

A good introduction to the primitives and how they may be used in conjunction with each other may be found in the widget demo script. Note that all the widget demos have a "Show Code" button. To help figure out what is happening in the script you may, when the window appears, edit the text and instrument the code with print statements and then simply press "Rerun Demo". Another place to see examples of the primitives (on the web) is at the image supplement to this FAQ at the following URL:

    http://w4.lns.cornell.edu/~pvhp/ptk/ptkIMG.html

Return to table of contents

10. How do I get widget X to do Y ?

There are a number of tasks that can be accomplished with perl/Tk widgets, configurations, and bindings (a few that can't and a few that require specific tricks). Beginners are encouraged to work through the examples in UserGuide.pod. Some examples from UserGuide.pod are addressed in this document among those that follow.

Basically a widget can be "created" by simply calling the sub of the same name:

    my $main = new MainWindow;

    $main->Button();

    my $button = $main->Button();

    $button -> pack;

    #!/usr/bin/perl -w
    use Tk;
    use strict;
    my $main = new MainWindow;
    my $button = $main -> Button();
    $button -> pack;
    MainLoop; 

    #!/usr/bin/perl -w
    use Tk;
    use strict;
    my $main = new MainWindow;
    my $button = $main->Button();
    $button -> configure(-text => 'Press me!');
    $button -> pack;
    MainLoop; 

    #!/usr/bin/perl -w
    use Tk;
    use strict;
    new MainWindow -> Button(-text => 'Press me!') -> pack;
    MainLoop; 

Do not overlook the - sign in front of some options (like -text in the above example) Another commonly overlooked problem is that elements in a hash are supposed to be strings hence a configuration option like -length +> 5, really ought to be specified as either '-length' +> 5, or "-length" +> 5, etc., rather than perl's builtin length() function.

Return to table of contents

10.1. How do I get a Button to call a Perl subroutine?

You may specify the -command option in the call to create & pack the button as in:

    $main->Button(-text => 'Print',
                   -command => sub{do_print($filename, $font)}
                   )->pack;

(Full source code for this and other examples from UserGuide.pod may be found at http://w4.lns.cornell.edu/~pvhp/ptk/pod/. To load code from the web save as a local file say ex1.pl, edit the first line to point to your perl interpreter, then change permission: %chmod u+x ex1.pl, then execute the script: %ex1.pl.)

The above method is called the "anonymous subroutine (closure)" method. As discussed in Callback.pod one might have re-written that statement to use the "reference to a sub" method thusly:

    $main->Button(-text => 'Print',
                   -command => [ \&do_print , $filename, $font ]
                   )->pack;

Return to table of contents

10.2. How do I get a Button to actively change under my mouse pointer?

You should specify both an '-image' and an '-activeimage' configuration option either when calling the ->Button() method or in a later separate call to the ->configure() method.

Here is an example excerpted from the basic_demo script that comes with the Tk kit:

    #!/usr/local/bin/perl -w
    
    use Tk;
    
    $main = MainWindow->new;
    
    $QPBFile  = "demos/images/QuitPB.xpm";
    $QPBaFile = "demos/images/QuitPBa.xpm";
    
    $QuitPB  = $main->Pixmap('-file' => Tk->findINC("$QPBFile"));
    $QuitPBa = $main->Pixmap('-file' => Tk->findINC("$QPBaFile"));
    
    my $but  = $main->Button('-image'       => $QuitPB,
                             '-activeimage' => $QuitPBa,
                             '-command'     => sub { $main->destroy }
                            ) -> pack;
    
    MainLoop;
    
    __END__
    

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10.3. How do I arrange the layout of my widgets?

To control the layout and appearance of widgets in a window one makes use of a geometry manager, as well as -padding, -fill, -expand, and -anchor options of individual widgets.

A geometry manager is any Tk procedure for controlling the arrangement of widgets in your application window. The predominant geometry manager used in both Tcl/Tk and perl/Tk is pack also known informally as the "packer" (other geometry managers are the "placer" and the canvas widget itself but are much less popular. There is also Nick Ing-Simmon's Table widget [discussed in a later question] and BLT_Table [which made it's way into perl/Tk thanks to Guy Decoux - but is also discussed in a later question]. So far tixForm is for Tcl/Tk only, but a perl/Tk version of Tix is in the works. You can invoke pack at the time of widget creation via calls like:

    $widget->pack;

    $widget(-option0 => value0,-option1 => value1)->pack;

    my $top2 = $main->Toplevel;
    my $frame = $top2->Frame;
    $frame->pack;
    $frame->Label(-text => 'Left2')->pack(-side => 'left');
    $frame->Label(-text => 'Right2')->pack(-side => 'right');
    $top2->Label(-text => 'Bottom2')->pack(-side => 'bottom');
    MainLoop;

(Full source code for this and other examples from UserGuide.pod may be found at http://w4.lns.cornell.edu/~pvhp/ptk/pod/. To load code from the web save as a local file say ex2.pl, edit the first line to point to your perl interpreter, change permission using: chmod u+x ex2.pl, then type the name of your script: ex2.pl.)

One of the more helpful options to pass to pack when trying to get a given widget layout "just right" is through padding: either -padx or -pady. The details of the use of pad depend on which specific widget you are trying to pack. In fact you can often add the -pad in the call to create the widget rather than in the call to pack.

There is also the -anchor configuration option for widgets. A good introduction to the 9 possible -anchor (and -overanchor) values is given by the popup demo in your perl/Tk build directory.

When setting a widget within a frame next to another widget one may wish to make use of the -fill => 'style' (where style = none | x | y | both) options of either pack or the widget itself. A typical situation where this is used is in setting up the Scrollbar next to a Canvas or Text widget.

Another aspect to consider when laying out your widgets is their behavior under resize operations (grabbing a part of the window frame and making it bigger or smaller - details depend on your window manager). This may be controlled by the -expand option of either pack or the widget itself.

Return to table of contents

10.4. How do I get a Popup to popup?

For things like a simple "are you sure?" dialog box you might want to take a look at Dialog.pm which is discussed in a later question within this FAQ [16.1].

If you don't wish to require Tk::Dialog, you need something more complicated, or you simply want to create your own independent window with widgets; you must first setup a Toplevel in perl/Tk. The fourth example in UserGuide.pod gives a simple example of how to call Toplevel. Quoting from that script:

    my $main = new MainWindow;
    fill_window($main, 'Main');
    my $top1 = $main->Toplevel;

The use of Toplevels brings up the issue of grab - or which independent window is presently "active" and which are activatable. To make a Toplevel window active call grab thusly:

    $Top_widget->grab(grab_option);

    $Top_widget->grab;

The use of Toplevels may also bring up the issue of focus - or which window - even which widget within a window - is presently "hot". You may call focus on an entire Toplevel:

    $Top_widget->focus;

To de-iconify a widget there is in fact a Popup function that may be called thusly:

    $Top_widget->Popup();

Return to table of contents

10.5. How do I bind keyboard keys?

There are many default key bindings built in to the widgets of perl/Tk. Making proper use of them often involves setting up the right callback. (You may wish to consult the examples in BindTable.pod for help with this subject.)

The basic idea is:

    $widget -> bind('<keyname>' => action);

    <Key> or <KeyPress> or <Any-KeyPress>
    <KeyRelease>
    <Button> or <ButtonPress>
    <ButtonRelease>
    <Button-1> or <B1> 
    <Double-1>
    <Enter>
    <Leave>
    <Motion>

    perl -ne 'print if s/.*(<[^>]*>).*/$1/g;' Button.pm

To get an idea of what the code is for a key that you are interested in try running the xlib_demo that comes in your perl/Tk build directory. Hold your mouse pointer over the window that appears and simply type the key that you are interested in. The code should appear in the window. If you do not have perl/Tk up and running yet try "xmodmap -pk" or look directly at the /usr/include/X11/keysymdef.h file where keysym names are given with an XK_ pre-pended. Do not try things like the Tcl/Tk %k symbols in perl scripts. %Ks will be mis-interpreted as non-existant perl hashes. Instead look at the Xevent function.

Ali Corbin <corbin@adsw.fteil.ca.boeing.com> recently posted a great little script for determining keyboard key bindings on a MainWindow:

    #!/usr/local/bin/perl -w
    use Tk;
    $top = MainWindow->new();
    $frame = $top->Frame( -height => '6c', -width => '6c',
                            -background => 'black', -cursor => 'gobbler' );
    $frame->pack;
    $top->bind( '<Any-KeyPress>' => sub
    {
        my($c) = @_;
        my $e = $c->XEvent;
        my( $x, $y, $W, $K, $A ) = ( $e->x, $e->y, $e->K, $e->W, $e->A );

        print "A key was pressed:\n";
        print "  x = $x\n";
        print "  y = $y\n";
        print "  W = $K\n";
        print "  K = $W\n";
        print "  A = $A\n";
    } );
    MainLoop();

    #!/usr/local/bin/perl
    use Tk;
    $top = MainWindow->new;
    $lb = $top->Listbox(-height => 10);
    for($i=0; $i < 120; $i++) {
      $lb->insert('end', $i);
    }
    $f = $top->Frame;
    $up = $f->Button(
           -text => "Up",
           -command => [ $lb->bind(ref $lb, '<Up>'), $lb]
           );
    $down = $f->Button(
             -text => "Down",
             -command =>sub {&{$lb->bind(ref $lb, '<Down>')}($lb)}
             );
    $up->pack(-side => 'left');
    $down->pack;
    $f->pack;
    $lb->pack;
    MainLoop;

Return to table of contents

10.6. How do I add bindings?

On Fri, 15 Sep 95 10:30:56 BST Nick Ing-Simmons <Nick.Ing-Simmons@tiuk.ti.com> writes:

Re: Multiple binds to a single widget?
**************************************

On Thu, 14 Sep 1995 14:57:54 -0400
Alain St <astdenis@cmc.doe.CA> writes:
!In the tcl/tk doc I have, they say that prepending the script 
!with '+' appends the new binding to the current one.
!
!How do I do that in perlTk? 
!

You cannot do that that way (yet?) - one issue is what it would mean to prepend '+' to a perl/Tk callback :

    $widget->bind('<A>','+',[\&subname,$arg]); 
    # did not look right to me

Other issue is that I would need to manage a list-of-callbacks in glue code.

Bind your new command to a new tag:

    $widget->bind('Extra',....);

And add Extra to the widgets bindtags:

    $widget->bindtags([ref($widget),$widget,'Extra',
                        $widget->toplevel,'all']);

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10.7. How do I bind the action of a slider (sic) to ... ?

Technically speaking they are called Scrollbars (not sliders) and one must configure the action of the desired widget to call the Scrollbars (i.e. bind is not involved here)

A common task using Scrollbars is to configure things like Canvas, Listbox, or a Text widgets to be updated (change appearance) when the slider of the acompanying Scrollbar is moved by the user.

As an example consider the code that sets up a twelve element Listbox and an accompanying vertical Scrollbar:

    my $main = new MainWindow;
    my $box = $main->Listbox(-relief => 'sunken', 
                             -width => -1, # Shrink to fit
                             -height => 5,
                             -setgrid => 'yes');
    my @items = qw(One Two Three Four Five Six Seven
                   Eight Nine Ten Eleven Twelve);
    foreach (@items) {
       $box->insert('end', $_);
    }
    my $scroll = $main->Scrollbar(-command => ['yview', $box]);

 
    $box->configure(-yscrollcommand => ['set', $scroll]);

There was an old Perl/Tk tendency to have a bunch of ScrlFoo widgets (such as ScrlListbox). The use of such widgets is now deprecated in favor of a new Scrolled class, as in:

    $w = $patent->Scrolled('Text',...);

• Canvas (::Axis)
• Entry
• Ghostview
• HList
• HTML (::Web)
• Listbox
• Pod
• Text (::ROText) (::TextUndo)
• Tiler

Return to table of contents

10.8. How do I configure a Scrollbar to scroll multiple widgets?

Note that the widget type that you wish to scroll can be important as a scroll "unit" on a Text or Listbox may be a character (several pixels - depending on font) whereas it would be an X "units" on a Canvas (could be pixel - but you may also specify other units).

A concrete answer for scrolling 3 Listboxes comes courtesy of Frederick L. Wagner <derf@ti.com>:

From a working example of multi-xscrolling:

    sub multiscrollx
    {  # multiscrollx
     my ($sb,$wigs,@args) = @ARG;
     my $w;
     foreach $w (@$wigs)
     {
       $w->xview(@args);
     }
    }  # multiscrollx
 
    # %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
      $sh->configure( -command => [ \&multiscrollx, $sh,
                         [$scratchrule,$ruleheader,$ruletable]]);
      $ruletable->configure(  -xscrollcommand => [ 'set', $sh]);
      $ruleheader->configure( -xscrollcommand => [ 'set', $sh]);
      $scratchrule->configure(-xscrollcommand => [ 'set', $sh]);

In this case,
$sh is a horizontal Scrollbar,
$ruletable and $scratchrule are Tables
$ruleheader is an Entry

However, this approach is good for any widget with X-scrolling capability, I think. So the Y counterpart should be:

    sub multiscrolly
    {  # multiscrolly
     my ($sb,$wigs,@args) = @ARG;
     my $w;
     foreach $w (@$wigs)
     {
       $w->yview(@args);
     }
    }  # multiscrolly
 
    # %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
      $sv->configure( -command => [ \&multiscrolly, $sv,
                                    [$l1,$l2,$l3]]);
      $l1->configure( -yscrollcommand => [ 'set', $sv]);
      $l2->configure( -yscrollcommand => [ 'set', $sv]);
      $l3->configure( -yscrollcommand => [ 'set', $sv]);

Hope that helps.

Greg VanSickle <vansickl@bnr.ca> points out that this little script snippet does not provide for the binding of '<Button-2<' that he is accustomed to. He wrote a package called DSListbox to address this binding issue.

Conversely, Jong Park asked how to setup multiple Scrollbars to scroll the same widget. Nick Ing-Simmon's reply makes use of an anonymous sub and can be summed up in a little script that scrolls a Text widget (to see the scrolling in action type more than 20 lines of text into the widget):

    #!/usr/local/bin/perl -w
    
    use Tk;
    my $mw = MainWindow->new();
    
    my $s1 = $mw->Scrollbar(-orient => 'vertical');
    my $s2 = $mw->Scrollbar(-orient => 'vertical');
    
    $s1->pack(-side => 'left', -fill => 'y');
    my $t = $mw->Text(
        -yscrollcommand =>  sub{$s1->set(@_), $s2->set(@_)},
        -wrap           => 'word',
        -width          => 70,
        -height         => 20, 
        -font           => $font,
        -setgrid        => 1,
    )->pack(-side => 'left');
    $s2->pack(-side => 'right', -fill => 'y');
    $s1->configure(-command => [$t => 'yview']);
    $s2->configure(-command => [$t => 'yview']);
    
    MainLoop;
    
    __END__

Return to table of contents

10.9. How do I display a bitmap?

You can display X bitmaps on your widgets with the -bitmap configuration option. Typically -bitmaps are configured into Label, Frame, Button, etc. widgets (Canvas widgets are another story however see question [11.1] below). In order to emphasize the bitmap option itself let us assume we were specifying a bitmap for a Label with a call like:

    $main->Label(-bitmap => 'bitmap-name')->pack;

In order to use some of the bitmaps in the perl5/Tk/demos/images/ directory you would specify a fuller path name like:

    $main->Label(-bitmap => "\@$tk_library/demos/images/face")->pack;

    $main->Label(-bitmap => '@foobar.xbm')->pack;
#or
    $main->Label(-bitmap => "\@foobar.xbm")->pack;

    $main->Label(-bitmap => "\@$ENV{'HOME'}/img/foobar.xbm")->pack;

Return to table of contents

10.10. How do I display an image?

You will want to get a "Photo" handle on the file as in the following example where 'imggif' is the Photo handle for a gif file that is distributed with perl/Tk:

    #!/usr/bin/perl -w
    use strict;
    use Tk;
    my $main = new MainWindow;

    $main ->Label(-text => 'Main')->pack;
    $main -> Photo('imggif', 
                   -file => "$Tk::tk_library/demos/images/earth.gif");
    my $l = $main->Label('-image' => 'imggif')->pack;

    $main->Button(-text => 'close',
                  -command => sub{destroy $main}
                  )->pack(-side => 'left');
    $main->Button(-text => 'exit',
                  -command => [sub{exit}]
                  )->pack(-side => 'right');
    MainLoop;

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10.11. What Image types are available?

In addition to the Tk builtin bitmaps there is support for reading images from files in formats such as: X11 Bitmaps (.xbm), X Pixmaps (.xpm), and Graphics Inline Format (.gif). See the CrtPhImgFmt man page for more info (if you have Tk 4.X installed). (In order to support other formats you might also consider running through a netpbm filter.)

For perl generation of images see the question (later in this FAQ) on graphics modules.

Return to table of contents

10.12. Is there any way to have more than one Listbox contain a selection?

To allow more than one Listbox to contain a "selection", (or at least a highlighted item - which need not be the actual selection) specify the configuration option:

    -exportselection => 0

Here is a rather simple script that illustrates what happens when only one Listbox has -exportselection => 0 specified:

    #!/usr/bin/perl -w
    
    use Tk;
    
    my $main = MainWindow->new;
    
    my @fruits = ('Apple','Banana','Cherry','Date','Elderberry','Fig');
    my @nuts   = qw(Almond Brazil Chestnut Doughnut Elmnut Filbert);
    
    my $fruit_list = $main->Listbox();
    for (@fruits) { $fruit_list -> insert('end',$_); }
    $fruit_list->pack();
    my $fruitprint_button = $main->Button(
                              -text => "print selection",
                              -command => sub{ printthem($fruit_list) }
                                          )->pack;
    
    my $nut_list = $main->Listbox(
                                  -selectmode => 'multiple',
                                  -exportselection => 0,
                                 )->pack;
    for (@nuts) { $nut_list -> insert('end',$_); }
    my $nutprint_button = $main->Button(
                              -text => "print selection(s)",
                              -command => sub{ printthem($nut_list) }
                                          )->pack;
    
    my $quit_button = $main->Button(-text => "quit program", 
                                    -command => sub{exit},
                                    )->pack();
    
    MainLoop;
    
    sub printthem {
        my $list = shift;
        my @entries = $list->curselection;
        for (@entries) { print $list -> get($_),"\n";}
    }

    http://w4.lns.cornell.edu/~pvhp/ptk/etc/lb-constructor

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10.13. How do I select a range of tags in a Text widget?

A question arose concerning getting a range of selections from a Text widget. Nick Ing-Simmons' answer mentions several possibilities including:

Keyboard Copy/Paste 'is' implemented of course...

Subj:	RE: $Text->tag('ranges', 'sel') - does this work?

In <199512291957.OAA02609@ohm.nrl.navy.mil>
On Fri, 29 Dec 1995 14:57:42 -0500
Charles J Williams <chas@ohm.nrl.navy.mil> writes:
!I was writing a little tk perl today, and i decided to try to 
!implement a copy/paste using the 'sel' tag
!
!I enabled exportselection, and then try to probe the select 
!region with:
!
!    $buffer = $text->tag('ranges', 'sel');
!
!$buffer comes back with one entry, the end of the selection.

That is to be expected - the scalar gets assigned the last element of the list.

!I tried:
!
!    @buffer = $text->tag('ranges', 'sel');
!
!same difference.

This seems to work for me:

    ($start,$end) = $text->tagRanges('sel');

In perl/Tk ->tagRanges(...) is an alias for ->tag('ranges',...)

The following subroutine can also probe and print the tagRanges:

    sub showsel  
    { 
     my $text = @_;
     my @info = $text->tagRanges('sel');
     if (@info)
      {
       print "start=$info[0] end=$info[1]\n" 
      }
    }

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10.14. How do I group Radiobuttons together?

Specify the -variable option on each one. Here is an example pulled from the icon.pl demo script:

     $letters = '';
     my $w_frame_left_b3 = $w_frame_left->Radiobutton(
         -bitmap   => "\@$tk_library/demos/images/letters",
         -variable => \$letters,
         -value    => 'full',
     );
     my $w_frame_left_b4 = $w_frame_left->Radiobutton(
         -bitmap   => "\@$tk_library/demos/images/noletters",
         -variable => \$letters,
         -value    => 'empty',
     );

Return to table of contents

10.15. How do I specify fonts?

The quick answer is to specify the font configuration option of your widget as in:

    #!/usr/local/bin/perl -w
    use Tk;
    $main = MainWindow->new();
    $labl = $main -> Label('-text' => "Foo", '-font' => "fixed");
    $labl -> pack;
    MainLoop;

The perl/Tk version of xfontsel was distributed as the font_test script in the Tk build directory.

See also the later question (within this FAQ) on international fonts.

Return to table of contents

10.16. How do I get the entry in an Entry?

You want to call get on the return value of the widget itself. Here is how it may be used in a simplified version of example 1.1 from the Tk::UserGuide where a Button is set up to call a sub where the call to get lies:

    #!/usr/bin/perl -w
    use strict;
    use Tk;

    my $main = MainWindow -> new();
    my $entry = $main -> Entry();
    $entry -> pack;
    $main->Button(-text => 'Print', 
                  -command => sub{do_print($entry)}
                  )->pack;
    MainLoop;

    sub do_print {
        my ($widget) = @_;
        my $entered = $widget -> get();
        print "The string \"$entered\" was entered.\n";
    }

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10.17. How do I hide a password Entry?

Set the -show option to zero, as in this example:

    $entry = $form->Entry(-textvariable => \$user_entry, 
                          -show => 0);

Return to table of contents

10.18. How do I limit an Entry's insertion width?

Nick Ing-Simmons recommends writing a new Entry widget with the insert method appropriately overridden by one that does limit the width. His code is avaialable as a separate package from:

    http://w4.lns.cornell.edu/~pvhp/ptk/etc/LEntry-0_00.tar.gz

    Date: Thu, 22 Aug 1996 10:32:44 -0400
    From: "Brent B. Powers" <powers@ml.com>
    Subject: Re: How to set max characters for Entry widget
    In-reply-to: <199608211445.PAA09248@pluto>
    
    Ummm, before we set this into the distribution or FAQ, maybe we should
    make it work properly.  An example:  Imagine maxwidth configured to 8,
    the user fills in ABCDEFGH, moves the cursor back 4 places, and types
    I.  The SUPER::insert call sets the string to ABCDIEFGH, which this
    code then modifies to ABCDIEFG.
    
    Hmmm, how about
    
    sub insert {
      my($w, @args) = @_;
      my($max) = $w->cget(-maxwidth);
      my($sval) = $w->get;
      if (length($sval) >= $max) {
         $w->SUPER::insert(@args);
         if (length($w->get) > length($sval) {
    	## Reject it;
    	my($idx) = $w->index('insert'); #  get current cursor position
            $w->delete(0, 'end');
            $w->insert(0, $sval);
            $w->icursor($idx);
    	$w->bell;
      } else {
         $w->SUPER::insert(@args);
      }
    }
    
    Of course, that still doesn't deal with the selection, but ... 

    'paste' and <ButtonRelease-2> call insert method, what other selection
    issues are there?

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10.19. How do I obtain Menus that do not tear off?

Nick Ing-Simmons outlined a couple of ways to achieve this result. The critical feature being the -tearoff => 0 configuration option of the Menu. In Nick's words:

    my $mb = $parent->Menubutton(...);    # The button
    my $menu = $mb->Menu(-tearoff => 0);  # Create a non-tearoff menu
    $mb->configure(-menu => $menu);       # Tell button to use it.
    $mb->command(....);

Above is for clarity - you can loose $menu variable:

    my $mb = $parent->Menubutton(...);  
    $mb->configure(-menu => $mb->Menu(-tearoff => 0));  
    $mb->command(....);

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11. How do I get a Canvas to ... ?

The Canvas widget is the most configurable and versatile. With versatility comes complication however, and it is certainly deserving of its own special section within this FAQ...

You might also see the examples in the widget demo especially the "canvas item types" selection (which runs the items.pl demo script).

Return to table of contents

11.1. Display a bitmap?

Unlike other widgets the Canvas does not take the -bitmap configuration option. One of the ways to place things - including bitmaps - onto a Canvas is to call create on it. To emphasize how a Canvas handles bitmaps differently from the configurable widgets let me assume that you wanted to specify the 'hourglass' built in bitmap in the following. (For more on xbm file specification see a previous question [10.9] within this FAQ.) Here is a way to combine the Canvas; and create; calls:

    my($canvar) = $main->Canvas();
    my($bittag) = $canvar->create('bitmap',10,10, -bitmap=>'hourglass');
    $canvar->pack;

    my($canvar) = $main->Canvas();
    my($bitmap) = $main->Bitmap(-data => $data);
    my($bittag) = $canvar->create(qw(image 10 10), -image => $bitmap);
    $canvar->pack;
    MainLoop;

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11.2. Erase a display?

To erase something like a bitmap call delete on the item. Assuming your Canvas tag is $canvar and your item tag it $bittag (as in the previous [11.1] question) then the call proceeds like:

    $canvar -> delete($bittag);

    $main->Button(-text   => 'clear', 
                  -command=>sub{$canvar -> delete($bittag)}
                 )->pack;

    $main -> withdraw;

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11.3. Display an Image?

Just as for the other widget types there is a two step process of first getting a "Photo" handle on the file of interest. For the Canvas (unlike the other widgets) one then makes a call to create an image as in the following example where 'IMG' is the Photo handle for a GIF file that comes distributed with the Tk kit (it just happens to be handled in this example via the scalar variable $img):

    #!/usr/bin/perl -w
    use strict;
    use Tk;
    my $main = new MainWindow;
    my $canvar = $main ->Canvas;
    $canvar->pack;
    my $file = 'demos/images/earth.gif';
    my $img = 
     $canvar->Photo( 'IMG', 
                     -file => Tk->findINC($file) );

    $canvar->create( 'image',0,0, 
                     '-anchor' => 'nw', 
                     '-image'  => $img );

    MainLoop;
    __END__

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11.4. What things can be created on a Canvas?

The following types can be used in $canvar->create calls:

    arc        sections of circle
    bitmap     for X11 bitmap files/builtins
    image      for Photo image types (gif, xpm, xbm, ...) 
    line
    oval       includes circles
    polygon    may be -filled
    rectangle  may also be -filled
    text       similar to Text widget primitive
    window     allows embeddding of other widgets

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11.5. How do I redraw a line on a Canvas?

By calling the ->coord method on the item as in the following example:

    #!/usr/bin/perl
    use Tk;
    $m = MainWindow->new;
    $c = $m -> Canvas;
    $i = $c -> create('line', 0,0 => 50,50 );
    $c -> pack;
    $b = $m -> Button('-text' => 'extend', 
                      '-command' => sub{push_it($c,$i)},
                     )->pack;
    MainLoop;
    
    sub push_it {
        my ($canvas, $line) = @_;
        $canvas -> coords($line, 0,0 => 100,100 );
    }

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11.6. How do I use the Canvas as a geometry manager?

In a call to create a window (or anything) on your Canvas you need to specify its position - this is in part how a Canvas can be used as a geometry manager. e.g.:

    my($bittag) = $canvar->create('bitmap',10,10, -bitmap=>'hourglass');

    tag  unit             example
         pixels           25,50   # i.e. no unit tag at all
    m    milliimeters     10c,20c
    c    centimeters      1c,2c
    p    points (1/72")   35p,70p

    Eric J. Bohm <bohm@cs.buffalo.edu> wrote:
    !I've got a row of entries packed side by side in a frame.  
    !These frames are packed on top of each other.  
    !So, when someone deletes a row, the lower ones bubble 
    !up automatically.  This works just fine and dandy, and let me
    !extend my thanks to our brave and energetic pTk team.
    !
    !The trick here is what widget do I put this in so that 
    !it will be scrollable when I have too many rows to 
    !fit on the screen?
      [details and complaints]

Following up to my own message here.

All right, after several false leads, I spent 3 hours fighting a canvas widget and pounding my head against the canvas.html doc, until I finally understood how to include my entries in a frame in a window in the canvas and get things to scroll nicely.

Turns out that the whole thing isn't all that hard to do once I understood how canvas widgets work.

Not sure if its of general interest, but here's the snippet, which was stolen from the items demo inside the widget_lib and then brutally hacked.

Perhaps a simpler demo would have been easier to use as a guide, but I got there eventually, so my thanks for the widget demo.

    #----------------------------------------
    my $c = $w_frame->Canvas();
    $c->configure(
         -height       => '300',
         -width        => '600',
         -relief       => 'sunken',
         -bd => 2,
     );
     my $w_frame_vscroll = $w_frame->Scrollbar(
                                         -command => ['yview', $c]
                                              );
     my $w_frame_hscroll = $w_frame->Scrollbar(
                                         -orient => 'horiz', 
                                         -command => ['xview', $c]
                                               );
     $c->configure(-xscrollcommand => ['set', $w_frame_hscroll]);
     $c->configure(-yscrollcommand => ['set', $w_frame_vscroll]);
     $w_frame_hscroll->pack(-side => 'bottom', -fill => 'x');
     $w_frame_vscroll->pack(-side => 'right', -fill => 'y');
     $c->pack(-expand => 'yes', -fill => 'both',-side=>'top');
     my $entryframe=$c->Frame;
     my $c_win= create $c 'window','0','0',
                          -window=>$entryframe,
                          -anchor=>'nw';
     #----------------------------------------

Where $c -> configure( -scrollregion => [$top, $left, $right, $bottom]) can be used to size things nicely once you find out how big it'll be.

And the widgets you want scrolled should be slaves of $entryframe.

Vastly more robust than anything I had running in the BLT Table.

EJB

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11.7. How do I get a Canvas to output PostScript(c)?

Many thanks to Tom Oelke <tpo9617@rit.edu> for providing this question, answer & snippet of code:

The following section of code gets the postscript code for the section of canvas that's top-left corner is at $min_x, $min_y, and has a width and height equivalent to the displayed region. This ps code is then piped out to lpr to be printed.

    my $ps = $canvas->postscript( '-x' => $min_x,
                                  '-y' => $min_y,
                                  -width => $canv->Width,
                                 -height => $canv->Height);
    open (PS, "| lpr"); # customize with -Pname e.g. 
    print PS $ps;
    close (PS);

    open (PS, ">file.ps"); # to output to a file
    print PS $ps;
    close (PS);

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11.8. How do I get a PostScript(c) output of a Canvas w/ widgets?

In general you don't. You can't do it in Tcl/Tk either (if that is any consolation). Nick Ing-Simmons posted an explicit discussion of what is involved:

Subj: RE: Canvases and postscript output

On Tue, 28 Nov 95 14:37:09 PST
Davis <morry@dsg.tandem.com> writes:
! I have a canvas with text and some entry widgets that I want to create
!postscript from. I used the 
!widget->postscript( -file => 'ld.ps', -colormode  => 'gray');
!the file gets created but its empty. Is there some other options I need?

Core Tk cannot write postscript for embedded windows, the best it could do would be to grab a Pixmap of the window as displayed. This is fine if the window is visible, but if it is scrolled off screen or under another application there is no pixmap.

Only complete fix is to have a ->postscript method for every possible widget which can render un-mapped widgets. This is non-trivial task.

!Also I have a scrollbar for this canvas and when I scroll  the entry widget
!actually scroll part way out of the frame the canvas is in. Why does this
!happen and can I fix it? 

The Entry widgets need to be descendants of the canvas or they just get clipped to their parent.

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11.9. How do I get the size of a Canvas? After a re-size?

    $canvas->cget(-width);

    $canvas->Width;

Nick Ing-Simmons points out that if you want to have your Canvas be able to grow to arbitrarily large sizes be sure to specify the -expand or -fill options when you ->pack the Canvas.

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11.10. How do I bind different actions to different areas of the same Canvas?

KOBAYASI Hiroaki <kobayasi@sowa.is.uec.ac.jp> recently posted an extraordinary little script that addresses this question quite succinctly:

How about this?
## I don't know whether this is a good solution or not.
## but it works under Tk-b9 + perl5.002b1f.

    
    #!/usr/local/bin/perl -w
    use Tk;
    
    ($c = MainWindow->new->Canvas)->
       pack(-fill => 'both', -expand => 1);
    # to survive under Tk-b8. 
    # You don't need paren before pack in b9.
    
    ($pop1 = $c->Menu)->command(-label => "FOO");
    ($pop2 = $c->Menu)->command(-label => "BAR");
    
    $c->create(oval => 0, 0, 100, 100, 
               -fill => 'black', 
               -tags => ['popup']);
    
    $c->Tk::bind($c, '<3>', [\&PopupOnlyThis, $pop1]);
    $c->bind('popup', '<3>', [\&PopupOnlyThis, $pop2]);
    
    sub PopupOnlyThis {
        print "@_\n";
        my($c, $pop) = @_;
    
        # to prevent multiple popup.
        Tk->break if defined $Tk::popup;
    
        my $e = $c->XEvent;
        $pop->Popup($e->X, $e->Y);
        # Tk::Menu::Popup sets $Tk::popup.
    
    }
    MainLoop;
    
    $Tk::popup = undef; # to kill warning.
    
    __END__

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12. Common Problems.

Everything in Tk-land is a reference. When defining callbacks take care to pass variables by reference. Callbacks are closures and to ensure a variable gets its current value, as opposed to its value when the callback is defined, pass by reference, e.g.:

    $frog = 123;
    $b = $mw->Button(
        -text    => 'Push Me',
        -command => [
            sub {
               my($widget, $frog) = @ARG;
               print STDERR "widget=$widget!\n";
               print STDERR "frog=$$frog!\n";
            }, $mw, \$frog,
         ],
    ); # end Button definition

If $frog is not passed by reference the print statement will always output "123" (actually, the print as it exists will print nothing since it's trying to dereference $frog, which presumably is now not a reference). Note that by definition all perl/Tk widgets are already references, since they're simply Perl objects, and that's why you do not have to print $$widget!

A good "reference" for handling references and dereferencing are the perlref(1) and perlobj(1) man pages. A good "reference" for the various data types you will encounter in this kind of perl programming is Tom Christiansen's Perl Data Structures Cookbook which is now available as the perldsc(1) man page.

Also beware the traps that befall perl4 programmers in making the move to perl 5. References for this include the new perltrap(1) man page as well as William Middleton's perl425 trap document at:

    http://www.perl.com/perl/all_about/perl425.html
or
    http://w4.lns.cornell.edu/~pvhp/ptk/misc/perl425.html

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12.1. What do the ->, => and :: symbols mean?

The -> is the "infix dereference operator". In other words it is the means by which one calls a sub with a pass by reference (among other things you can do with ->). As stated above most things in calls to perl/Tk routines are passed by reference. The -> is used in perl just as in C or C++. (Most of the widget primitives are elements of the Tk:: "perl class".) A simple example of dereferencing would be:

    $x = { def => bar };  # $x is a reference to an anon. hash
    print $x->{def},"\n"; # prints ``bar''

    my($top) = MainWindow->new;

    my($top) = new MainWindow;

    $top -> Widge-type;

    http://www.metronet.com/perlinfo/perl5.html

The => digraph is simply a synonym for the comma operator. It's useful for documenting arguments that come in pairs.

    $query -> Button(-in,\$reply,-side,'left',-padx,2m,-pady,
     2m,-ipadx,2m,-ipady,1m)->pack(-side,'bottom');

    $query ->Button( -in => \$reply,
                     -side => 'left',
                     -padx => 2m,
                     -pady => 2m,
                     -ipadx => 2m,
                     -ipady => 1m
                    )->pack(-side => 'bottom');

While the :: symbol can be thought of as similar to the period in a C struct, it is much more akin to the :: class scope operator in C++:

    a.b.c;       /* something in C */
    a::b::c();   // function in C++ 
    $a::b::c;    # a scalar in Perl 5
    @a::b::c;    # a list in Perl 5
    %a::b::c;    # an associative array or "hash" in Perl 5
    &a::b::c;    # a function in Perl 5

    $main'foo;   # a $foo scalar in perl 4
    $main::foo;  # a $foo scalar in Perl 5

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12.2. What happened to the ampersands &?

Perl 4 programmers especially may be surprised to find that as of Perl 5.0 the ampersand & may be omitted in a call to a subroutine if the subroutine has been declared before being used. Actually you can even get around the declare before omit ampersand rule by using the subs.pm pragma, or by pre-declaring (without defining) as in a script like:

    #!/usr/bin/perl -w
    use strict;
    use Tk;
    sub Mysub;  #pre-declare allows calling Mysub()

    ...Other main/Tk stuff - 
            including call to Mysub() sans &...

    sub Mysub {

        ...Mysub stuff...

    }

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12.3. What happened to the quotation marks?

Perl 4 programmers especially may be surprised to find a serious dearth of quotation marks around strings in perl 5 scripts such as in perl/Tk. The "rules have been relaxed" somewhat for the use of quotation marks. Basically it is OK to leave them out if the context of the string in question is unambiguous. However, it never hurts to leave them in and may help readability.

Here is Larry Wall's synopsis of the string situation:

Newsgroups:

comp.lang.perl.misc

Subject:

Re: To string or not to string...

In article <4e49fv$j0u@panix3.panix.com>,
Andy Finkenstadt <genie@panix.com> wrote:
! Back when I was learning perl (after receiving a review copy of
! learning perl, and buying the real perl book, each from ORA),
! I always got bit by when I needed to use "strings" and when
! I could get away with bare_words within braces for associative
! arrays.  (Yes, this is under 4.036 if it matters.)
! 
! the most typical example would be:
! 
! When must I use $assoc{"trailer"} and when can I get away with
! $assoc{trailer}?   Similarly, $ENV{CONTENT_LENGTH} versus
! $ENV{"CONTENT_LENGTH"}?  Unfortunately sometimes my strings
! end up being numbers in their own right, i.e.:  $message{"0"}
! or $msg=0; $message{$msg}.  Which is more appropriate,
! which are merely stylistic, and which are stricly perl5
! features now that I'm upgrading most of my installations
! of perl.

Perl 4 let you use a "bareword" for a string if it had no other interpretation. It would warn you under -w if you used a word consisting entirely of lower-case characters, since such a word might gain an interpretation someday as a keyword.

Perl 5 still works the same way, but with several twists.

1. ) Since you can now call predeclared subroutines as though they were builtins, you have to worry about collisions with subroutine names too. However...
2. ) You can completely disallow the default interpretation of barewords by saying "use strict subs", which requires any such bareword to be a predeclared subroutine. But...
3. ) Overriding all that, Perl 5 (in recent versions) will FORCE string interpretation of any bare identifier used where a single hash subscript is expected, either within curlies or before a =>. (Those are the places you might usually want the old barewords anyway.)

The upshot of these rules is that you can write Perl 5 with much less punctuation than Perl 4, yet also with less ambiguity. If you so choose.

Larry

Tcl programmers should note that in Perl the single quotation marks '' act much as the curly brace {} enclosure does in Tcl (no escaping special characters $@\ etc.). Whereas the double quotation marks "" allow for substitution of $variables (the rules are a little different between Tcl and Perl however).

Note also that a frequently seen short hand in perl5/Tk scripts is the @list returned by qw():

    @list = qw(zoom schwartz bufigliano);

    @list = split(' ','zoom schwartz bufigliano');

    @list = ('zoom','schwartz','bufigliano');

There are, ironically enough, situations in perl/Tk where one needs to use quotation marks as in the following by post by <a904209@pluto.tiuk.ti.com>:

 Paul Wickman wrote in article <4b4o0fINNlu8@CS.UTK.EDU>:
!
!    Why does the following statement work fine:
!
!$day->pack(-before => $year, -side => 'left');
!
!    But the below generates the given error:
!
!$day->pack(-after => $year, -side => 'left');
!
!Ambiguous use of after => resolved to "after" => at line 191.
!

Because there is a sub after in scope, probably imported from Tk via use Tk;.

There are two workrounds:

    use Tk qw(MainLoop exit ...); # just ones you use

or

    $day->pack('-after' => $year, -side => 'left');

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12.4. Must I use "my" on all my variables?

If you use strict; (as recommended) the answer is "probably". This confines the variables names to your namespace - so your variable does not conflict with one in the module(s) your are using (you are at the least useing Tk;). my does "lexical scoping" on a variable rather than the "dynamic scoping" done by local (like auto variables in C). The difference between these two is that the scope of my $var is confined to the block (sub, if, foreach, etc.) in which it is declared and used, as opposedto local $iable which can propogate to all blocks called by the block in which it is declared. In general the confined scope of my $var means that its use will proceed quicker and more efficiently than local $iable.

If you give a fully qualified variable name such as

    $main::var = 1;  # No "my" needed

If you choose to use my (as recommended) then beware that you should declare a variable my only at the first use (instantiation) of a variable. Consider yet another way to re-write the "Hello World!" script:

    #!/usr/local/bin/perl -w
    use strict;
    use Tk;
    my $main = new MainWindow;
    my $label = $main->Label(-text => 'Hello World!');
    my $button = $main->Button(-text => 'Quit',
                               -command => sub{exit});
    $label->pack;  #no "my" necessary here
    $button->pack; #or here
    MainLoop;

James M. Stern points out that redundant my declarations are not simply useless they can be dangerous as in the following script which will not work:

    #!/usr/local/bin/perl -w
    use strict;
    use Tk;
    my $main = new MainWindow;
    my $label = $main->Label(-text => 'Hello World!');
    my $main;   #WRONG: this $main overrides previous
    my $button = $main->Button(-text => 'Quit', #will now fail
                               -command => sub{exit});
    $label->pack;  
    $button->pack; 
    MainLoop;

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12.5. Is there a way to find out what is in my perl/Tk "PATH"?

Presuming this question is asking for a little more than the answer you get when you type:

    ls perl5/lib/Tk/*.pm

    #!/usr/bin/perl
    
    use Tk;
    require 'dumpvar.pl';
    
    dumpvar('Tk');

    perl -e 'use Tk; require "dumpvar.pl"; dumpvar("Tk");'

If you wish to determine the Configuration options a given widget accepts (and what the values are at a given point in a script) you may use the ->configure method with no arguments to retrieve the list of lists, as in this example:

    #!/usr/bin/perl
    
    use Tk;
    my $main = MainWindow -> new;
    my $scrl = $main -> Scrollbar('-orient' => 'horizontal');

    @scrollconfig = $scrl -> configure;
    for (@scrollconfig) {
        print "@$_\n";
    }
    
    etc.

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12.6. What is the difference between use and require?

The short answer is that something like:

    use Tk;

    BEGIN { require "Tk.pm"; import Tk; }

    ftp://ftp.perl.com/perl/info/everything_to_know/use_vs_require

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12.7. How do I change the cursor/color?

Nick Ing-Simmons <nik@tiuk.ti.com> and others posted a series of answers to this type of question. In summary what they said was:

Basically

    $mw->configure(-cursor => ... );

Unless you use one of built-in cursors it gets messy.

Here copy of what Tk/demos/color_editor does:

    #!/usr/local/bin/perl -w
    use Tk;
    my $mw = MainWindow->new;
    $mw->configure(-cursor => ['@' . Tk->findINC('demos/images/cursor.xbm'), 
                                    Tk->findINC('demos/images/cursor.mask'),
                                     'red', 'green']);
    MainLoop;

That says that argument to -cursor is a list of 4 things:

1. . Pathname to bitmap with '@' prepended to say it isn't a built in name (Using findINC to locate file relative to Tk install location.)
2. . Pathname to mask bitmap (no @ required)
3. . Foreground colour
4. . Background colour

! I want to remap it for the MainWindow
! and will be using a pixmap.

You won't be using a Pixmap with normal X11. X11 allows *bitmap* with optional mask (another bitmap), and two colours.

The optional nature of the mask means that a simple call with a list reference like:

    $mw->configure(-cursor => ['watch', 'red', 'blue']);

should work alright.

You may also obtain the value of the default cursor for a widget using something like ->optionGet.

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12.8. How do I ring the bell?

The short answer is

   $widget -> bell;

    #!/usr/bin/perl
    use Tk;
    $main = MainWindow -> new;
    $butn = $main->Button(-text => 'bell')
    $butn->configure(-command => sub{ $butn->bell; });
    $butn->pack();
    MainLoop;

    #!/usr/bin/perl
    use Tk;
    $main = MainWindow -> new;
    $but = $main->Button(-text => 'bell', 
                         -command => sub{ringit($main)})->pack;
    MainLoop;
    
    sub ringit { 
        my $m = shift; 
        $m->bell; 
    }

some systems remap this [the "console bell"] to anything from a digital sound to a flash on the screen.

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12.9. How do I determine the version of perl/Tk that I am running?

With an up to date perl installation one may query the local perl setup and all extensions via the command:

    perldoc perllocal

Tk-b10++:
Tk-b10 (and higher) has changed to $Tk::VERSION (rather than the older "$Tk:Version") to be consistent with other packages. Hence a short succinct way to tell which version you have installed (that works with Tk-b11 and Tk400.200) is:

    perl -MTk -e 'print $Tk::VERSION."\n"'

Tk-b9.01:
The version numbers as of Tk-b9.01 are stored in the following variables:

    Core Tk version : $Tk::version
    Tk patchLevel :   $Tk::patchLevel
    library :         $Tk::library
    perl/Tk Version : $Tk::Version 

    perl -e 'use Tk; print "$Tk::Version\n";'

older                         Tk-b9.01++
packslaves                    pack('slaves')
packpropagate                 pack('propagate')
packForget                    pack('forget')
                              pack('info')

$w->delete if ($w);            $w->destroy if ($w);

Tk-b8(--):
A little script (Tk_module) can tell you and return the value:

    #!/usr/bin/perl
    use Tk;
    local(*Tk_m) = \$Tk::Tk_module;
    print "$Tk_m\n";

    perl -e 'use Tk; print "$Tk::Tk_module\n";'

    perl -e 'use Tk; print "$Tk::tk_version\n";'

All Tk versions:
Don't forget that you can always determine your Perl version/patchlevel/etc. with:

    perl -v

OZAWA Sakuro <ozawa@prince.pe.u-tokyo.ac.jp> points out some ways to do it in a script:

1. '$]' holds the version number.
2. In Perl5, 'require NUMBER;' will complain if version is younger than NUMBER. (e.g. require 5.001;)
3. Of course, newly imported (and incompatible) features in newer scripts will bailout before execution if parsed by an old interpreter.

To determine your MakeMaker version number try something like this (5.002):

    perl -MExtUtils::MakeMaker -e 'print "$ExtUtils::MakeMaker::VERSION\n";'

    perl -e 'use ExtUtils::MakeMaker;print"$ExtUtils::MakeMaker::VERSION\n";'

    perl -e 'use ExtUtils::MakeMaker;print"$ExtUtils::MakeMaker::Version\n";'

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12.10. How do I call perl from C?

You need to see a recent copy of the perlembed(1) pod page. By "recent" it needs to be up to date with at least perl5.002.

Borrowing from Jon Orwant's preamble to that document:

Do you want to:

Use C from Perl?

Read (at least) the perlcall(1), the perlapi(1), the perlxs(1), the perlxstut(1), and the perlguts(1) manpages.

Use C++ from Perl?

Recent changes to MakeMaker will make this easier. Be sure you are familiar with the perlcall(1), the perlapi(1), the perlxs(1), the perlxstut(1), and the perlguts(1) manpages.

Use an executable program from Perl?

Read about backquotes ``, system(), and exec() built in perl functions. Try reading the perlfunc(1) manpage.

Use Perl from Perl?

Read about do, eval, use and require. The perlfunc(1) manpage discusses these. For complete scripts you may also make use of the backquotes ``, system(), or exec() built in perl functions, but you may take a performance hit in doing so (see perlfunc(1) for information).

Use C from C?

Rethink your design.

Use C++ from C++?

See previous.

Use Perl from C?

Read (at least) the perlembed(1) and the perlguts(1) manpages.

Use Perl from C++?

Read (at least) the perlembed(1) and the perlguts(1) manpages.

    http://www.osf.org/~dougm/perl/Devel-embed-*.tar.gz
or
    http://www.perl.com/cgi-bin/cpan_mod?module=ExtUtils::embed

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12.11. How do I call Tcl code from perl/Tk?

Assuming that you have a pressing need to call Tcl from perl/Tk then one "official way" to so would be via the ->send() and the ->Receive() methods.

It is also worth noting that you can still have access to a complete Tcl script from perl via the perl system, or `` (backtick), or even exec mechanisms. Just be careful with I/O waits and return values if you try one of these approaches. Further suggestions may be found in the various perlipc files at:

    ftp://ftp.perl.com/perl/info/everything_to_know/

#!/usr/local/bin/perl
#####################################################################
#  An example of calling wish as a subshell under Perl and
#  interactively communicating with it through sockets.
#
#  The script is directly based on Gustaf Neumann's perlwafe script.
#
#  Dov Grobgeld dov@menora.weizmann.ac.il
#  1993-05-17
#####################################################################

    $wishbin = "/usr/local/bin/wish";

    die "socketpair unsuccessful: $!!\n" unless socketpair(W0,WISH,1,1,0);
    if ($pid=fork) {
	    select(WISH); $| = 1;
	    select(STDOUT);

	# Create some TCL procedures
	    print WISH 'proc echo {s} {puts stdout $s; flush stdout}',"\n";

	# Create the widgets
	print WISH <<TCL;
	# This is a comment "inside" wish

	frame .f -relief raised -border 1 -bg green
	pack append . .f {top fill expand}

	button .f.button-pressme -text "Press me" -command {
	    echo "That's nice."
	}
	button .f.button-quit -text quit -command {
	    echo "quit"
	}
	pack append .f .f.button-pressme {top fill expand} \\
		       .f.button-quit {top expand}
TCL
	# Here is the main loop which receives and sends commands
	# to wish.
	while (<WISH>) {
	    chop;
	    print "Wish sais: <$_>\n";
	    if (/^quit/) { print WISH "destroy .\n"; last; }
	}
	    wait;
    } elsif (defined $pid) {
	open(STDOUT, ">&W0");
	open(STDIN, ">&W0");
	close(W0);
	select(STDOUT); $| = 1;
	exec "$wishbin --";
    } else {
	die "fork error: $!\n";
    }

    http://sun20.ccd.bnl.gov/~ptk/archive/ptk.1995.11/0057.html

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13. What are some of the primary differences between Tcl/Tk and Perl/Tk?

Considering that both interpreters/(compiler) for Tcl and Perl were written in C for original use on Unix computers it is not surprising that there are some similarities between the two languages.

Nevertheless, there are a large number of differences between the Tcl language and the Perl language. One thing to keep in mind is that to build, install, and use Perl/Tk one does not need to have Tcl/Tk on hand at all. Perl/Tk is completely independent of Tcl/Tk.

Tom Christiansen (a definite perl proponent) has put up a web page that elucidates some critical technical differences between Tcl and Perl at:

    http://www.perl.com/perl/versus/tcl-discussion.html

With Tk-b9.01 (and higher) a great many functions (method calls actually) start with an upper case letter and continue with all lower case letters (e.g. there is a perl/Tk Entry widget but no entry widget), and many configuration options are all lower case (e.g. there is a perl/Tk highlightthickness option but no highlightThickness option). Thus if you are having trouble converting a script check your typing. (there is a script b9names to help). There is also a tcl2perl script (discussed later).

The html docs that get created during the build of perl/Tk ought to help clarify most any language difference. While the following table does not cover all the differences it is hoped that it will prove useful, especially to those people coming from a primarily Tcl/Tk programming background. These are some of the common Tcl->Perl stumbling points:

what              Tcl/Tk                 Perl/Tk
variable          set a 123              $a = 123; or $a = '123';
 initialization
re-assignment     set b $a               $b = $a;

lists/arrays      set a {1 2 fred 7.8}   @a = (1,2,'fred',7.8);
re-assignment     list set b $a          @b = @a;

associative       set a(Jan) 456.02      %a = ('Jan',456.02,'Feb',534.96);
 arrays           set a(Feb) 534.96
re-assignment     foreach i \            %b = %a;
                   [array names a] {
                   set b($i) = $a($i) }

Note on the above examples:
In Tcl the scalar, list, and array variable 'a' will overwrite each 
previous assignment.
In Perl $a, @a, %a are all distinct (occupy separate namespaces).

expressions       set a [expr $b+$c]     $a = $b+$c;

increment         incr i                 $i++; or ++$i;

declare           proc plus {a b} {      sub plus { my($a,$b) = @_;
 subroutines       expr $a + $b }         $a+$b; }

variable scope    local default          global default
                  override w/ "global"   override w/ "my" (or "local")

call              plus 1 2               &plus(1,2); #or
 subroutines                             plus(1,2);  #OK after sub plus

statement sep     newline or at ";"      ";" required

statement         "\" - newline          none required
 continuation

verbatim strings  {}                     ''
 e.g.             {a \ lot@ of $stuff}   'a \ lot@ of $stuff'

escaped strings   ""                     ""
 e.g.             "Who\nWhat\nIdunno"    "Who\nWhat\nIdunno"

STDOUT            puts "Hello World!"    print "Hello World!\n"
                  puts stdout "Hello!"   print STDOUT "Hello!\n"

   canvas .frame.canvas -yscrollcommand ".frame.scroll set" ; #Tcl/Tk OK
   canvas .frame.canvas -yscroll ".frame.scroll set" ;        #Tcl/Tk also OK
   $canvas=$main->Canvas(-yscroll => ['set',$scroll]);  #ERROR perl/Tk
   $canvas=$main->Canvas(-yscrollcommand => ['set',$scroll]); #perl/Tk OK

   require 'abbrev.pl';
   %foo = ();
   &abbrev(*foo,'-yscrollcommand');
 ...
   $canvas=$main->Canvas($foo{'-yscroll'} => ['set',$scroll]); #perl/Tk OK

    use Shell;
    print($p = man(-k => bitmap));

    man -k bitmap

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14. How do I install new scripts | modules | extensions?

(Thanks to Ilya Zakharevich <ilya@math.ohio-state.edu> for pointing out that perl code comes in a variety of flavors and some code requires more work than others to install. Hence I have expanded this topic and will refer to three distinct categories here: Scripts Modules and Extensions:)

Scripts

Other things you do not want to forget when trying to run a perl script include giving yourself permission to do so, e.g.:

    chmod u+x newscriptname

If you are still experiencing difficulty check to be sure that extraneous /newsgroup|e-mail|HTML headers|footers|markup//; are not in the file and that you have on hand all that is requireed or useed by the script (if not you may need to install a module - or even a perl4 style lib.pl file).

Modules

    #!/usr/bin/perl -w
     BEGIN { @INC = ("$ENV{'PWD'}",@INC); }
     use Tk;
     use Foo;

    #!/usr/bin/perl -w
     use lib $ENV{PWD};
     use Tk;
     use Foo;

    perl -Ipath/to/Foo -e fooscriptname

After a successful test; if you are a system administrator, or have root priveleges, or are modifying your own copy of perl; then copy it to the perl5/Tk directory. Depending on how the module was written it should be possible to use it either with the use Tk; statement itself or with an explicit use Tk::Foo; (for module perl5/Tk/Foo.pm).

Extensions (Overgrown Modules)

    perl Makefile.PL

    perl Makefile.PL
    make
    make test
    make install

    perl -MCPAN -e 'install "Foo"'

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15. How do I write new modules?

You might want to start by poking around your perl/Tk build directory. Is there something there that already does what you want? Is there something that is reasonably close - but only requires minor modification?

Next go through the various perl documents - including the FAQ as well as the various relevant man pages: perlmod(1), perlobj(1), perlbot(1), (and please don't forget: perlpod(1)!)

Post your idea to comp.lang.perl.tk and discuss it with others - there might very well be someone working on an approach already. A clear explanation of all the stuff that gets put into a module was posted to the mailing list and can be found in the archive at:

    http://sun20.ccd.bnl.gov/~ptk/archive/ptk.1995.10/0012.html

    http://www.perl.com/CPAN/modules/00modlist.long.html
    ftp://rtfm.mit.edu/pub/usenet/news.answers/perl-faq/module-list
    ftp://ftp.demon.co.uk/pub/perl/db/mod/module-list.txt
    ftp://ftp.wpi.edu/perl5/Modules/module_list.txt

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16. Composite Widgets.

Composite widgets combine the functions of two or more widget primitives into something that is not quite a stand alone program but is something that may prove very useful for inclusion in your own scripts. A variety of composite widgets have been written and many are still being worked on. Many come bundled with your perl/Tk distribution kit, and some are simply posted to comp.lang.perl.tk. It is quite common to have composite widgets written in perl modules - usually in terms of the Tk widget primitives. Graphical examples of some of the composites discussed here can be seen by GUI browsers at:

    http://w4.lns.cornell.edu/~pvhp/ptk/ptkIMG.html

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16.1. How do I get a Dialog box?

For things like a simple "are you sure?" dialog box you might want to take a look at perl5/Tk/Dialog.pm. This module may be invoked with require Tk::Dialog; etc. - there are much more extensive directions inside the comment fields at the top of the Dialog.pm file itself. The module has a lot of options and has a tutorial driver script in perl5/Tk/demos/dialog. Dialog.pm is also used by the perl5/Tk/demos/widget demo. In particular look at perl5/Tk/demos/widget_lib/dialog1.pl and dialog2.pl for examples of how one makes use of Tk::Dialog. A snippet of a script that uses this module could look like:

    require Tk::Dialog;

    my $mw = MainWindow->new;
    my $D = $mw->Dialog(
                 -title => 'Are you sure?',
                 -text  => "You have requested rm \*\nAre you sure?",
                 -default_button => 'No',
                 -buttons        => ['No','yes']
                       );
    my $choice = $D->Show;  # use Show for Tk-b9.01
# if using Tk-b8:    my $choice = $D->show;

    print " you chose $choice \n";

<Greg_Cockerham@avanticorp.com> wrote:
! I want to reconfigure the colors of the Dialog and
! ErrorDialog buttons.  How do I do this?
! Thanks in advance.

   $dialog_widget->configure(-background => 'purple'); 

Since these two widgets are composites you manage them like any 'ol widget. If the default delegate subwidget(s) aren't to your liking you can always get to individual component widgets of the composite via the ->Subwidget() method.

I see these subwidgets:

Dialog

'message' is the label subwidget with the dialog text, and 'bitmap' is the label subwidget showing the dialog bitmap

ErrorDialog

'error_dialog' is Dialog subwidget, 'text' is text subwidget

You can even do things like this:

 $error_dialog->Subwidget('error_dialog')->
                    Subwidget('bitmap')->configure(..);

to "get to" the label widget of the dialog component of the error_dialog widget.....

Be sure to also check out the "dialog" demo.

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16.2. Is there a file selector?

Yes, there may be several eventually...

One distributed with the perl/Tk code kit itself is called FileSelect.pm and was written by Frederick L. Wagner - (based on an original by Klaus Lichtenwalder).

Another module called SelFile.pm was adapted by Alan Louis Scheinine from Wagner's FileSelect.pm. It is available from:

    http://sun20.ccd.bnl.gov/~ptk/archive/ptk.1995.11/0122.html
or
    http://w4.lns.cornell.edu/~pvhp/ptk/etc/SelFile.pm

    http://sun20.ccd.bnl.gov/~ptk/archive/ptk.1995.10/0093.html
or
    http://w4.lns.cornell.edu/~pvhp/ptk/etc/FileSave.pm

    http://sun20.ccd.bnl.gov/~ptk/archive/ptk.1995.12/0201.html
or
    http://w4.lns.cornell.edu/~pvhp/ptk/etc/FileDialog.pm

    http://w4.lns.cornell.edu/~pvhp/ptk/etc/SaveAs.pm

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16.3. Is there a color editor?

There is. Please see

    perldoc ColorEditor.pm

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16.4. Is there a round Scale?

It is not quite a "round Scale" but Roy Johnson has written "Dial.pm" for round dial (or speedometer) -like settable widgets. It is available from:

    http://sun20.ccd.bnl.gov/~ptk/archive/ptk.1995.08/0431.html
or
    http://w4.lns.cornell.edu/~pvhp/ptk/etc/Dial.pm

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16.5. Is there something equivalent to tkerror?

Yes there is. Please see the Tk/ErrorDialog.pm module for further information.

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16.6. Are there Tables?

There are least two:

Nick's Table

    http://w4.lns.cornell.edu/~pvhp/ptk/etc/Table.pm.html

Guy Decoux's BLT_Table

    ftp://moulon.inra.fr/pub/pTk/

    http://w4.lns.cornell.edu/~pvhp/ptk/etc/Table.html

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17. Programming/development tools.

There are a number of tools and methods to help you with your perl/Tk scripting and development. It is worthwhile to note here that the -w switch is recommended as is the use strict; statement near the top of your script/program. If it dies and you still cannot decrypt the error message that these generate take a look though man perldiag(1).

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17.1 Is there a Tcl/Tk to perl/Tk translator?

Nick Ing-Simmons has written a (rather lengthy) tcl2perl script. It is distributed with the perl/Tk build kit. Please handle carefully! (translation: do not expect it to translate arbitrary tcl code accurately nor even into the most efficient perl/Tk equivalent. Do go over the converted script with care - and do not forget -w and use strict;.) Thanks Nick :-)

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17.2 Is there something equivalent to wish in perl/Tk?

The answer is yes.

The idea of wish is that you read from <STDIN> and evaluate each statement. The standard way to do this in perl/Tk is to use the tkpsh script that comes in your perl/Tk build directory. Another elegant way to get wish like behavior in perl/Tk is to use rmt which you can find in perl5/Tk/demos in your perl/Tk distribution. When you run rmt you already have Tk.pm set up for you so you can start typing things like $mmm = new MainWindow; etc. at the rmt: prompt. (This use belies the power of rmt which is derived from Ousterhout's Tcl/Tk version of rmt [see section 27.2 of his book]. rmt is capable of "inserting Tk code" into simultaneously running Tk applications.)

A cruder way to get wish-like behaviour with perl/Tk is to run a "perl shell" and type in your usual commands, including use Tk; etc. There is a script distributed with perl called perlsh which is written quite simply as:

    #!/usr/bin/perl
     $/ = '';        # set paragraph mode
     $SHlinesep = "\n";
     while ($SHcmd = <>) {
         $/ = $SHlinesep;
         eval $SHcmd; print $@ || "\n";
         $SHlinesep = $/; $/ = ''; 
     }

KOBAYASI Hiroaki has a more sophisticated wish like perl/Tk "shell" that is called EVA. It is available from:

    ftp://ftp.sowa.is.uec.ac.jp/pub/Lang/perl5/Tk/eva-*.tar.gz

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17.3. Is there a debugger specifically for perl/Tk?

Not for the latest version - but the -w switch and use strict; are always helpful with debugging as they provide informative error messages.

You can, of course, run under the standard perl debugger using the -d switch like so:

    perl -d myscript

(Older information): Gurusamy Sarathy <gsar@engin.umich.edu> had built a PERL5DB file called Tkperldb (which despite the name is for pTk not Tk/perl). One must install an early de-bugger then apply a patch to bring the debugger up to date. The early debugger kit was available from:

    ftp://ftp.perl.com/pub/perl/ext/TK/Tkperldb-*.tar.gz

 You need a post 5.001m perl that has support for debugging closures. 
 Or you can simply apply:

   http://www-personal.umich.edu/~gsar/perl5.001m-bugs.patch

 to 5.001m. (5.002beta includes all the fixes in the above patch).

    $ENV{'PERL5DB'} = 'BEGIN { require Tkperldb }';

Keep in mind that you are programming in perl after all. The perl debug line mode is available to you through executing the following from your shell:

    perl -de 0

Ilya Zakharevich <ilya@math.ohio-state.edu> points out that very recent perldb versions will allow for simultaneous X and STDIN reads. He also points out:

Note that you may use 

    sub myLoop {
      if (defined &DB::DB) {
        while (1) {             # MainWindow->Count
          Tk::DoOneEvent(0);
        }
      } else {
        MainLoop;
      }
    }

(and I hope the analogous provision will be in MainLoop in 
 tk-b9 - hi, Nick ;-)

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17.4. Is there a GUI builder in perl/Tk?

Work has reputedly (January 1996) started on porting a Tcl/Tk GUI builder known as SpecTcl for use with perl/Tk. For the Tcl/Tk SpecTcl kit see:

    ftp://ftp.sunlabs.com/pub/tcl/SpecTcl-*.tar.[gz|Z]

In <news:ANDREAS.96Mar24234521@marvin.berlin.de> Andreas Koschinsky <marvin@logware.de> announced a perl script for use with SpecTcl that has some interesting capabilies:

24 Mar 1996 22:45:21 GMT
... So i wrote a perl-script that can convert project-file (.ui-files) which spectcl writes. The script reads the .ui-file and generates an equivalent perl-module.

    ftp://susan.logware.de/pub/incoming/ui2perl*.tar.gz

Somewhat more removed from SpecTcl there is also SWIG.

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18. Processes & Inter-Process Communication under Perl/Tk.

Inter-Process Communication (IPC) is the subject of spawning and controlling other programs or "processes" from within perl (sometimes using sockets to do so). The subject is briefly discussed in the perlipc(1) man page, and was addressed towards the end of Chapter 6 of The Camel. The subject is also discussed in the perl FAQ and at Tom Christiansen's ftp site (in the various perlipc* files) at:

    ftp://ftp.perl.com/perl/info/everything_to_know/    199.45.129.30

    http://www.perl.com/perl/everything_to_know/ipc/index.html

Remember:

If a packet hits a pocket on a socket on a port,
And the bus is interrupted as a very last resort,
And the address of the memory makes your floppy disk abort,
Then the socket packet pocket has an error to report!
-Ken Burchill(?)

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18.1. How does one get Perl/Tk to act on events that are not coming from X?

On 22 Nov 1995 (Yaniv Bargury) bargury@milcse.cig.mot.com wrote:

I need to write a GUI monitor, that displays the status and controls a set of processes running in the background. The idea is to have the GUI application start a few child processes, command the children through pipes from the GUI to the children, and display the children status coming on pipes from the children to the GUI in real time.

The GUI must not be busy waiting, because the CPU resources are limited. This excludes using the Tk_DoWhenIdle as explained in the manual.

The usual way to do this is to for the GUI process to have one select() in its main loop. That select() should wait for X events or input from the pipes leading from the children.

How do you do this?

fileevent - it is the hook into the select() in the mainloop.

In addition Avi Deitcher <avi@morgan.com> replied with:

I wrote something similar to effectively do a tail -f on multiple hosts, displaying the result on separate text widgets. Do the following:

    parent
     child
     child
     child
     ..

with a one-way pipe from each child to the parent. Set up the following:

    $main->fileevent(FILEHANDLE,status,subroutine);

for each pipe that you have. This will cause pTk to monitor the FILEHANDLE and call 'subroutine' when an event happens on that handle. In this case: FILEHANDLE = pipename status = 'readable' or 'writable' or 'exception' and subroutine = any subroutine that you want.

To provide a concrete example of fileevent usage Stephen O. Lidie wrote a wonderful little GUI tail monitor he calls tktail:

    #!/usr/local/bin/perl -w
    #
    # tktail pathname
    
    use English;
    use Tk;
    
    open(H, "tail -f -n 25 $ARGV[0]|") or die "Nope: $OS_ERROR";
    
    $mw = MainWindow->new;
    $t = $mw->Text(-width => 80, -height => 25, -wrap => 'none');
    $t->pack(-expand => 1);
    $mw->fileevent(H, 'readable', [\&fill_text_widget, $t]);
    MainLoop;
    
    sub fill_text_widget {
    
        my($widget) = @ARG;
    
        $ARG = <H>;
        $widget->insert('end', $ARG);
        $widget->yview('end');
    
    } # end fill_text_widget

    echo Hello from foo! > foo
    tktail foo &
    echo \"A ship then new they built for him/of mithril and of elven glass\" --Bilbo \
     >> foo

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18.2. Is there a send and do I need xauth?

There is a Tk::send, but to use it own must write one's own version of Tk::receive. An example of this may be found in the rmt program distributed with perl/Tk. Note that as of Tk-b12 (including the released version Tk400.200) the script that receives from a Tk::send must run with taint chcecking turned on (i.e. with the -T switch thrown) and it must untaint all commands received from the other process.

The Tk::send <-> Tk::receive process will work under xhost + authority. The security this affords comes from the fact that anyone who would want to exploit it would have to know how to write a Tk::receive custom tailored to your application (in addition to all the other protocol hacking).

Please note that while you may not need xauth authorization it is nevertheless always a good idea.

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18.3. How can I do animations using after?

There is a "toggling button" demo script supplied with Tk called after_demo that makes effective use of after().

Terry Greenlaw <terry@encompass.is.net> of Encompass Technologies posted a character cell animator for the really bored. Here it is in a slightly modified form that allows string input from the command line (note too the recursive call that doesn't sop up system memory):

#!/usr/bin/perl

=head1 NAME

From: z50816@mip.lasc.lockheed.com "Terry Greenlaw"  Thu Feb 1 12:02:24 EST 1996
To: ptk@guest.WPI.EDU
Subj: A code sample for the REALLY bored

For everyone with a case of Browser envy after using Microsoft's Internet
Explorer, here's a perl/tk script only slightly more useful than a script
to do <BLINK>. Don't know why I wrote it. Don't know why you'd run it.
Maybe if you were writing a ticker tape application. Or had a weird thing
for Times Square. Anyway....

tog
Terry Greenlaw (on-site @ Lockheed Martin)      Encompass Technologies
z50816@mip.lasc.lockheed.com                    terry@encompass.is.net

##################################################################

=cut

    #!/usr/bin/perl
    
    #use strict;
    use Tk;
    
    $message=join(' ',@ARGV,''); 
    if (!$message) {
        $message="THIS IS A VERY LONG SCROLLING MESSAGE...      ";
        $topmssg="This is the top of the screen";
        $botmssg="This is the bottom of the screen";
    }
    else {
        $topmssg=$message;
        $botmssg=$message;
    }
    $top = MainWindow->new;
    $l1 = $top->Label(-fg => 'White', -text => $topmssg);
    $l1->pack(-fill => 'both', -expand => 1 );
    $m1 = $top->Label(-fg=>'Red', -bg=>'black',
                      -textvariable => \$message, 
                      -width => 15 
                      );
    $m1->pack();
    $m2 = $top->Label(-wrap=>1, 
                      -fg=>'Green', -bg=>'black',
                      -textvariable => \$message2, 
                      -width=>1, -height=>8 
                      );
    $m2->pack(-anchor=>'w');
    $l2 = $top->Label(-fg => 'White', -text => $botmssg);
    $l2->pack(-fill => 'both', -expand => 1 );
    
    after(100, \&scroll_it);
    
    $top->MainLoop;
    
    sub scroll_it {
        $message =~ /(.)(.*)/;
        $message="$2$1";
        ($message2 = $message) =~ s/ /  /g;
        after(100, \&scroll_it);
    }
    __END__

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18.4. How do I update widgets while waiting for other processes to complete?

The short answer is either

    $widget -> update;
or
    $widget -> DoOneEvent;

    #!/usr/bin/perl -w
    
    use Tk;
    
    my $m = MainWindow->new();
    my $l = $m -> Listbox();
    $l -> bind('<Double-1>' => sub{sleepy($l)} );
    my @nuts   = qw(Almond Brazil Chestnut Doughnut Elmnut Filbert);
    for (@nuts) { $l -> insert('end',$_); }
    $l -> pack;
    MainLoop;
    
    sub sleepy {
        my $widget = shift;
        print "before 1st sleep \n";
        sleep(10);
        print "after 1st sleep before delete \n";
        $widget -> delete('active');
        $widget -> update;             # try [un]*commenting this
        print "after delete before 2nd sleep \n";
        sleep(10);
        print "after 2nd sleep \n";
    }
    __END__

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18.5. How do you fork on System V (HP)?

Kraegeloh Martin <mkr@dm-server.cv.com> originally asked:

! Subj: signal handling difference on HP vs. SUN
!
! the following code will fork an xterm with vi in it, and it
! will refuse to do so while the first xterm is still running.
! works fine on my sun.
! On HP however, the second time an xterm is started, NO handler
! is called when the child dies.
!
! the code:
! ===================== 8< ===============================
! $SIG{CHLD}=\&w;
!
! sub w{
!    $pid=wait;
!    print STDERR "died: $pid\n";
!    if ( $have == $pid ) { $have = 0; }
! }

I suspect HPUX is SysV-ish not BSD or POSIX. So every time a signal fires, it removes the handler - you need to reset it in the handler:

    sub w{
        $SIG{CHLD}=\&w;
        $pid=wait;
        print STDERR "died: $pid\n";
        if ( $have == $pid ) { $have = 0; }
     }
 

Whether you reset it before/after the wait may be very important ...

Then Bjarne Steinsbo <bjarne@hsr.no> followed up with:

That's not the whole story... Another problem is that SIGCLD interrupts the read system call on SysV-ish (I like that word! :-) systems. This means that you have to test why "" fails, and act accodingly. A program that works on both Sun and HP is:

    $SIG{CHLD}=\&w;
    while(1){
       $_ = ;
       $! = 0, next if $! =~ /Interrupted/;
       last if $! or !defined $_;
       if($have){
            print STDERR "child still alive\n";
       }
       else{
            if(($pid=fork()) != 0){
               $have=$pid;
               print STDERR "forked $pid\n";
            }
            else {
               exec("xterm -e vi") 
            }
       }
    }

    sub w{
       $pid=wait;
       print STDERR "died: $pid\n";
       if ( $have == $pid ) { $have = 0; }
       $SIG{CHLD}=\&w;
    }

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19. How do I "clear the screen"?

What screen are you trying to clear?

If you are trying to clear a tty (e.g. xterm) screen then try either of the following within your script:

    system "clear";
or
    print `clear`;

David and Rachel Weintraub <davidw@cnj.digex.net> recommend using the old termcap.pl p4 library. You might also consider the perl 5 equivalents: Term.pm (especially the Term::Control module), Curses.pm, Perlmenu.pm, PV.

Returning to X-windows and perl/Tk: if you are trying to eliminate a TopLevel or a MainWindow then try:

    $main -> destroy;

    $main->withdraw;    # remove

    $main->deiconify;   # put back

    $w->pack('forget'); # remove if packed (newer Tk-b9.01++) 
    $w->packForget;     # remove if packed (older versions)
    $w->pack(...);      # put back

    $w->UnmapWindow; 

If you are trying to erase an $item on a Canvas then try:

    delete($item);

(Thanks to the post by <a904209@pluto.tiuk.ti.com> which extended this answer considerably.)

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20. Is there a way to have an X application draw inside a perl/Tk window?

(This question was posed by Andrew Allen March 19 1997):

No not yet. But according to Nick Ing-Simmons:

If app. can take XID of window to draw on it should be doable now,
but if Tk has to pro-actively watch for creation of app's 'top level',
and "capture" it is more tricky.

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21. Is there a version for Microsoft Windows(tm)?

Yes. Tk402.000 is in alpha release at this time (Spring 1997) and builds with perl 5.004, nmake, and Visual C++ on at least Windows NT.

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22. Are there any international font packages for perl/Tk?

In principle you may specify the -font configuration option on all your Button, Entry, Label, Message, etc. widgets. In addition to the Unix programs xfontsel and xlsfonts you may find xset useful for determining and/or specifying fonts - especially international ones.

KOBAYASI Hiroaki <kobayasi@sowa.is.uec.ac.jp> has converted the Tcl/Tk "japanization" by <nisinaka@sra.co.jp> so that it may be used with perl/Tk. It is presently available (the current README file is in Japanese) from the following ftp site:

    ftp://ftp.sowa.is.uec.ac.jp/pub/Lang/perl5/Tk/

Currently, the "japanization patch for perl/Tk" enables:

  [1] To show kanji & ASCII (by choosen kanji-font) in every widget.
  [2] To edit kanji (double width of ASCII) correctly in Text & Entry.
  [3] To support of Kanji Input method. (tkKinput.c)
  [4] Automatic kanji-code-detection & conversion with 'insert/get'.
      Supports: "JIS(Japanese Industrial Standard)", "MS-KANJI", "EUC".

& the patch lacks:

  [5] by manual Kanji-code conversion. (JIS <=> MS-KANJI <=> EUC)
  [6] 'Good' interface to specify kanji-code used in internal. (tkWStr.c)
  [7] Documentation in English about [1-6].
      # but, since interface-change is suspected in near future, 
      # documenting them is ...

I thought that[5-7] was not enough for world-people, but already worth
for natives. So I announced it on "fj.lang.perl".

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23. Are there any other ways to create event based interfaces from perl?

Yes. A short list would have to mention these for X:

For perl 4:

WAFE, STDWIN

For perl 5:

Sx (uses Athena & Xlib), Motif (uses Motif & Xt), Fresco (post X11R6.1). This perl extension was originally written by Dominic Giampaolo, but was re-written for Sx by Frederic Chauveau. The code is available from CPAN in the authors/Frederic_Chauveau/ directory.

There is an X11::* hierarchy of perl->X modules under development and available from CPAN.

For hooking into the C++ Qt library there is Ashley Winters' PerlQt.

The Perl 5 Module List has a listing of User Interfaces (Character and Graphical).

Further information on X interfaces to Perl is provided in the perl FAQ.

For primarily graphics (with some user interface programming) there is also an OpenGL Perl Module of particular interest to anyone with either OpenGL or the MesaGL library. This package allows for compact perl VRML scripting. If you would like to see the OpenGL network X demonstration go to:

    http://www.arc.ab.ca/vr/opengl/examples/

    http://www.arc.ab.ca/vr/opengl/plugin.html

For perl generation of images see the question in this FAQ on graphics modules.

The X window system is not the only means of doing event based user interface programming in perl. There is, for example, William Setzer's Curses modules for perl 5 too.

For Active X scripting on Windows try the PerlScript package from

    http://www.activeware.com/

which will work with Internet Explorer, Internet Information Server, as well as the wscript command line interface.

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24. Where can I get more information on graphics (modules|scripts)?

To generate server side push animation in perl please see the perl cgi FAQ. To generate GIF89a loops from a collection of stills visit the Gifloop page at

   http://www.homecom.com/gifanim.html

There are several graphics modules in perl already available - with several more still under development. Among them:

GD.pm

The GD.pm perl module is a perl interface to the C code of a similar name and was written by Lincoln Stein. It allows for the generation of GIF (Graphics Inline Format) images from within a perl script. The module itself is available from any CPAN ftp site, and Lincoln maintains an informational web page at:

    http://www-genome.wi.mit.edu/ftp/pub/software/WWW/GD.html

gd/GIF.pm

The gd/GIF.pm module is similar to GD.pm (generates GIFs using gd.c) and was written by Roberto Cecchini who maintains a web page for his module at:

    http://www.fi.infn.it/pub/perl/GIF/

JPEG.pm

The JPEG.pm module was written by Nick Ing-Simmons expressly for use with the Tk family of modules. It is distributed on CPAN in the authors/id/NI-S/ directories as a Tk-JPEG-*.tar.gz file.

Open/Mesa-GL Perl Module

This module can use the OpenGL lib on computers that have it (available for SGI, AIX, Linux), or with the MesaGL package (which allegedly runs a little slower but does not require the X accelerator hardware that OpenGL does). This package supports relatively easy graphics programming, 3D shading, etc. Very cool stuff! The URL for the OpenGL perl module is:

    http://www.arc.ab.ca/vr/opengl/

PGPERL

If you will be interfacing to the PGPLOT FORTRAN language routines you might consider Karl Glazebrook's PGPERL which has an interactive web demo as well a a web home page at:

    http://www.aao.gov.au/local/www/kgb/pgperl.html

    #!/usr/bin/perl
    use PGPLOT;
    use Tk;
    open(IMG,"test.img");       # Read 128x128 image from binary file 
    read(IMG, $img, 4*128*128); # data - list of 4 byte float [C type]
    close(IMG);                 # stored as perl string.
    pgbegin(0,'test.gif/gif',1,1);
    pggray($img,128,128,1,128,1,128,1,0,*tr); # pg-Plot it
    my $main = new MainWindow;
    $main ->Label(-text => 'Main')->pack;
    $main -> Photo('IMG', -file => "test.gif");
    my $l = $main->Label('-image' => 'IMG')->pack;
    $main->Button(-text => 'close',
                  -command => sub{destroy $main}
                  )->pack(-side => 'left');
    $main->Button(-text => 'exit',
                  -command => [sub{exit}]
                  )->pack(-side => 'right');
    MainLoop;                    # pg-tk plot it

perlDL

perlDL or PDL is the Perl Data Language for fast manipulation of large arrays - such as those that often occur in image processing/analysis/creation (or scientific data sets). PDL is also by Karl Glazebrook. This is a very hot module full of programmer convenience features such as overloaded operators etc. There is a mailing list and a home page for this module:

    http://www.aao.gov.au/local/www/kgb/perldl/
    perldl-request@jach.hawaii.edu
    http://www.rosat.mpe-garching.mpg.de/mailing-lists/perldl/

    http://sunsite.unc.edu/pub/Linux/apps/graphics/convert/INDEX.short.html

Other programming tools/utilities are of help with graphics. The X11 release contains many such tools. There is also The GIMP. Consider also the ImageMagick program.

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25. Are there any major applications written in perl/Tk?

Yes. In fact, there are some interesting perl/Tk applications already available from:

Your very own perl/Tk distibution:

program        description
pfm            perl file manager - cute iconic front to emacs
ptknews        a GUI perl newsreader - a work in progress.
tkpsh          perl/Tk equivalent of the Tcl/Tk wish shell.
toyedit        a Text widget editor.

program        description
browse         Simple file browser front end for emacs.
color_editor   Front end to Tk::ColorEditor
               allows RGB, CMY, and HSV color cube manipulation
               (based on tcolor.tcl).
ixset          GUI front end to xset - for terminal settings.
pgs            Perl front end to Ghostscript (viewing PostScript(c) files).
rmt            perl/Tk 
               "development shell/remote control application"
               You can launch or talk to other perl/Tk apps with rmt.
rolodex        Like the Tcl/Tk app of the same name.
               Requires editing for personal use.
timer          Stopwatch-like seconds timer.
tkpod          The perl gui pod viewer (like xman).
tkweb          The perl "Rough and Ready" web browser.

Menu Perl
{
    "Perl"          f.title
    "editor"        f.exec "toy_edit &"
    "tkemacs"       f.exec "browse &"
    "manual"        f.exec "tkpod perl.pod &"
    "the web"       f.exec "tkweb http://www.perl.com/perl/ &"
    "news"          f.exec "ptknews comp.lang.perl.tk &"
    "pgs"           f.exec "pgs &"
    "stop watch"    f.exec "timer &"
}

# We bind it so that left mouse button when pressed while 
# over the root or background pops up with this Perl menu:
Buttons DefaultButtonBindings
{
    <Btn1Down>      root       f.menu  Commands
    # etc.
}
Buttons ExplicitButtonBindings
{
    <Btn1Down>      root       f.menu  Commands
    # etc.
}

Other perl/Tk application distributors:

ptkb.pl

an xbiff like mailbox watcher. Available from ftp://ftp.wpi.edu/perl5/pTk-Modules/ptkb.pl

bioTkperl

Was announced by Gregg Helt <gregg@fruitfly.berkeley.edu> recently. See the home page at: http://www.cbil.upenn.edu/~dsearls/bioTk.html. Source at: ftp://fruitfly.berkeley.edu/pub/bioTk/bioTkperl0.8.tar.gz

EVA

KOBAYASI Hiroaki's EVA is a sophisticated wish like perl/Tk "shell". It is available from: ftp://ftp.sowa.is.uec.ac.jp/pub/Lang/perl5/Tk/eva-*.tar.gz

plop

Stephen Lidie's very useful arbitrary function Plot Program, was featured in the premier issue of The Perl Journal and is available on the web at: http://tpj.com/tpj/programs/Vol_1_Issue_1_Tk/plop

modo

Yet another Lidie creation. This one hails from Issue 2 of The Perl Journal

neko (et al.)

In the third issue of The Perl Journal Stephen Lidie makes creative use of approaches to event timing from perl/Tk. neko is one axample.

Workspace

Is an integrated front end to the fvwm window manager that makes use of Perl/Tk. See the web page at http://www.mirai.com/wks/ for more information.

www

The original 8 line wonder by Jon Orwant. Pick it up (and modify it) from: http://sun20.ccd.bnl.gov/~ptk/archive/ptk.1995.08/0411.html. (Please note: www is for amusement, the more serious perl/Tk browser - tkweb - is distributed with perl/Tk and it is "only" 60 lines long!.)

ptkclock & ptkmines

From the generous software archive of Jason Smith at RPI.

XCricket

This application was written by Nem Schlecht.

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26. What is the history of pTk and perl/Tk?

This list is only slowly coming together. Please forgive any absences.

• tkperl5a5 is announced Thu, 20 Oct 1994 14:44:23 +0000 (BST)

NOTE
This project is unrelated to the one which is adding usersubs to
perl4 to get access to Tk via Tcl. Often, postings on comp.lang.perl
just say "tkperl" without saying which one is meant. They are two
totally different kettles of fish.

--Malcolm (Beattie)

• Fri, 25 Nov 94 14:29:53 GMT Nick Ing-Simmons is working on what will be known as "nTk" eventually.
• Mon, 12 Dec 94 08:56:36 GMT, Nick Ing-Simmons reports:

I have a re-port of ext/Tk nearly ready for alpha.
It builds its own "pTk" library from sources semi-automatically derived
from Tk3.6.  There is no Tcl library at all. 

Would anyone like to assist me in testing it?

• nTk-a2 announced Fri, 16 Dec 1994 10:59:36 -0500
• nTk-a3 announced Mon, 19 Dec 1994 18:03:27 -0500
• nTk-a5 announced Fri, 23 Dec 1994 10:18:16 -0500 (last to use Tk 3.6 ?)
• nTk-a6 first to use Tk 4.0 (?)
• nTk-a7 announced Fri, 13 Jan 1995 10:55:27 -0500
• nTk-a8 has appeared before Tue, 17 Jan 95 09:04:33 GMT
• nTk-a9 has appeared before Wed, 18 Jan 95 19:25:10 GMT
• nTk-a10 announced Tue, 24 Jan 1995 14:32:02 -0500
• nTk-a11 announced Tue, 31 Jan 95 19:05:32 GMT
• Malcolm Beattie suggests the nTk -> Tk name change, Larry Wall concurs
• nTk-a12 announced Thu, 16 Feb 1995 09:12:26 -0500
• Nick Ing-Simmons calls for a new mail list Thu, 16 Feb 95 14:13:55 GMT
• Tk-a13 announced Wed, 1 Mar 1995 11:38:15 -0500 (Name has changed from "nTk")
• Tk-b1 announced Tue, 14 Mar 95 16:58:40 GMT
• Tk-b2 announced Wed, 29 Mar 95 15:52:44 BST
• Tk-b3 announced Fri, 31 Mar 95 16:54:54 BST
• Tk-b4 announced Fri, 12 May 1995 11:45:32 -0400 EST
• Tk-b5 announced Mon, 26 Jun 95 17:14:06 BST
• Tk-b6 announced Fri, 21 Jul 95 15:42:35 BST
• Tk-b7 announced Fri, 28 Jul 95 15:16:02 BST
• Tk-b8 announced Wed, 16 Aug 95 12:34:05 BST
• an RFD (Request For Discussion) for a new usenet group comp.lang.perl.tk is circulated by Jon Orwant Fri, 4 Aug 1995 08:29:46 -0400
• unmoderated newsgroup comp.lang.perl.tk passes by a vote of 352 to 18 with 1 abstention in an announcement made Mon, 9 Oct 1995 10:13:17 -0400 (EDT). The new group makes its appearance at news-servers roughly 18 October 1995.
• Tk-b9.01 announced Wed, 20 Dec 95 10:06:47 GMT.
• Tk-b10 announced Sat, 23 Mar 96 17:16:27 GMT.
• Tk-b11 announced Mon, 1 Apr 96 16:44:48 GMT.
• Tk-b11.01 announced Wed, 3 Apr 96 17:48:09 GMT.
• Tk-b11.02 announced 10 Apr 96 12:52:28 GMT.
• Tk-b12 announced 28 August 1996.
• Tk400.200 announced 6 September 1996.
• Tk400.201 announced Fall 1996.
• Tk400.202 announced Late Fall 1996.
• Tk402.000 (alpha release for Windows) announced May 1997.

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27. What can we expect the future to hold?

With the production release of Tk400.202 and the alpha release of Tk402.000 the future of this code looks quite bright. (Hopefully the FAQ maintainer will manage to keep up :-).

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28. How do I obtain the latest version of this FAQ?

On the world wide web

Plaintext (whole):
http://w4.lns.cornell.edu/~pvhp/ptk/ptkFAQ.txt
Plaintext (multi-part):
http://w4.lns.cornell.edu/~pvhp/ptk/ptkFAQ0.txt
http://w4.lns.cornell.edu/~pvhp/ptk/ptkFAQ1.txt
http://w4.lns.cornell.edu/~pvhp/ptk/ptkFAQ2.txt
http://w4.lns.cornell.edu/~pvhp/ptk/ptkFAQ3.txt
http://w4.lns.cornell.edu/~pvhp/ptk/ptkFAQ4.txt
http://w4.lns.cornell.edu/~pvhp/ptk/ptkFAQ5.txt
or gzipped PostScript(c) (about 60 US 8.5"x11" pages):
http://w4.lns.cornell.edu/~pvhp/ptk/ptkFAQ.US.ps.gz
or gzipped PostScript(c) (about 60 A4 pages):
http://w4.lns.cornell.edu/~pvhp/ptk/ptkFAQ.A4.ps.gz

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29. Acknowledgements & maintainer.

The Perl/Tk extension to the Perl programming language is copyrighted by its author Nick Ing-Simmons <nik@tiuk.ti.com> whose Tk400.202/COPYING file reads as follows:

Copyright (c) 1995-1996 Nick Ing-Simmons. All rights reserved.
This package is free software; you can redistribute it and/or
modify it under the same terms as Perl itself, with the exception
of the files in the pTk sub-directory which have separate terms
derived from those of the orignal Tk4.0 sources and/or Tix.

IN NO EVENT SHALL THE AUTHORS OR DISTRIBUTORS BE LIABLE TO ANY PARTY
FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
ARISING OUT OF THE USE OF THIS SOFTWARE, ITS DOCUMENTATION, OR ANY
DERIVATIVES THEREOF, EVEN IF THE AUTHORS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.

THE AUTHORS AND DISTRIBUTORS SPECIFICALLY DISCLAIM ANY WARRANTIES,
INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT.  THIS SOFTWARE
IS PROVIDED ON AN "AS IS" BASIS, AND THE AUTHORS AND DISTRIBUTORS HAVE
NO OBLIGATION TO PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR
MODIFICATIONS.

See pTk/license.terms for details of this Tk license, 
and pTk/Tix.license for the Tix license.

In addition, this FAQ has benefitted from the contributions of many people all over the net to whom I am quite grateful.

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