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Subject: comp.lang.perl.tk FAQ part4 of 5

This article was archived around: Sun, 01 Jun 1997 06:42:26 GMT

All FAQs in Directory: perl-faq/ptk-faq
All FAQs posted in: comp.lang.perl.tk, comp.lang.perl.announce
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Summary: comp.lang.perl.tk Frequently Asked Questions. Archive-name: perl-faq/ptk-faq/part4 Posting-Frequency: monthly Last-modified: Date: Sat May 31 16:48:37 1997 URL: http://w4.lns.cornell.edu/~pvhp/ptk/ptkFAQ.html Version: 1.00_07
URL (Hypertext-split): http://w4.lns.cornell.edu/~pvhp/ptk/ptkTOC.html URL (Plaintext): http://w4.lns.cornell.edu/~pvhp/ptk/ptkFAQ.txt Image-supplement: http://w4.lns.cornell.edu/~pvhp/ptk/ptkIMG.html ftp-Archive: ftp://ftp.ccd.bnl.gov/pub/ptk/ptkFAQ.txt ftp-Archive: ftp://rtfm.mit.edu/pub/usenet/perl-faq/ptk-faq/ e-mail-Archive: ptkfaq@pubweb.bnl.gov Perl/Tk FAQ part 4 of 5 - More Perl/Tk ************************************** ______________________________________________________________________ 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 Within each language there is Tk - a widget Toolkit. One must be careful that some of the Tcl/Tk widget names and options have been modified slightly in the perl/Tk language. 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" Note also that Tcl/Tk has a built-in abbreviation completion mechanism that lets you specify short hand, e.g. 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 You may get around this with the perl abbrev.pl package in certain circumstances. For example: require 'abbrev.pl'; %foo = (); &abbrev(*foo,'-yscrollcommand'); ... $canvas=$main->Canvas($foo{'-yscroll'} => ['set',$scroll]); #perl/Tk OK In Perl you can emulate the Tcl unknown proc (through the perl AUTOLOAD mechanism) as follows: use Shell; print($p = man(-k => bitmap)); Which is equivalent to what you would get if you typed: man -k bitmap >From within tclsh or wish. (Thanks to Ilya Zakharevich <ilya@math.ohio-state.edu> for pointing out this feature. ;-) ______________________________________________________________________ 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 ------- A "self-contained" script needs little modification (in principle!) to run. It is a good idea to check the #! line at the very top of the file to reflect your local perl setup (e.g. #!/usr/bin/perl -w (change to) #!/usr/gnu/local/perl -w or what have you). There are allegedly "more portable" ways to invoke the perl interpretor as well - they are more fully documented in the perl FAQ and the perlrun(1) man page, however. 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 You also want to be sure your DISPLAY environment variable is set up properly when attempting to run a perl/Tk script. You may also need to look at the xhost(1) or the xauth(1) man pages for setting up your X-display properly. 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 ------- Check out the module - make sure it is OK and will run on your system - does it require a specific location? For testing purposes (always a good idea) or if you do not have root priveleges set the file in a directory that you do have write access to and try to include it in a test script. Assuming you have a module to test called "Foo.pm" and are simply running the test script in the same directory as the module begin by adding to the @INC array like so: #!/usr/bin/perl -w BEGIN { @INC = ("$ENV{'PWD'}",@INC); } use Tk; use Foo; or #!/usr/bin/perl -w use lib $ENV{PWD}; use Tk; use Foo; Another approach is to set either the PERLLIB or PERL5LIB environment variable from your shell. This method allows invoking the test script from within a number of different directories without having to edit a hard coded use lib or push(@INC,".") kind of statement within the script. Yet another way to do it is with the -I switch on the command line like so: 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) ------------------------------ These may come as a multi-file kit (tape archive usually) and may require a C compiler for part of the installation (perl/Tk itself falls into this category). You know you have an Overgrown Module (Extension) when there is one or more files with an .xs extension (perl->C meta code) and a Makefile.PL (perl->make meta code). One invokes the perl MakeMaker on the file called Makefile.PL in order to create a Makefile via: perl Makefile.PL You may now run make on the resultant Makefile - but the details of this process are module dependent and should be documented in a README or an INSTALL file. A very standard perl extension requires 4 (or 5 if making static) standard commands to make and install: perl Makefile.PL make make test make install If you have the appropriate CPAN and FTP modules already installed you can retrieve a module from CPAN and carry out all of the above steps with a perl one-liner like this: perl -MCPAN -e 'install "Foo"' ______________________________________________________________________ 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 Also, be sure to check out a recent version of the official Module List that Tim Bunce <Tim.Bunce@ig.co.uk> and Andreas Koenig <a.koenig@franz.ww.TU-Berlin.DE> maintain and post to comp.lang.perl.announce periodically. The list is also available at any CPAN ftp site as well as: 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 Finally ready to ship? Small (perl/Tk) modules have been posted directly to comp.lang.perl.tk. Big modules may require ftp distribution (see upload info at one of the CPAN sites) then make your announcement to comp.lang.perl.tk and possibly to comp.lang.perl.announce. ______________________________________________________________________ 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 ______________________________________________________________________ 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"; A question concerning configuration of the Subwidgets on the Dialogs came up recently: <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. ______________________________________________________________________ 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 A module called FileSave.pm allows one to type in a new (non-existant) filename for "Save as..." type operations. It was posted by Mark Elston on 12 Oct 1995 to the mailing list and is available from: http://sun20.ccd.bnl.gov/~ptk/archive/ptk.1995.10/0093.html or http://w4.lns.cornell.edu/~pvhp/ptk/etc/FileSave.pm A slightly different behaviour is to be had with Brent B. Powers' FileDialog.pm that was posted to the mailing list on 12 Jan 1996 and available from: http://sun20.ccd.bnl.gov/~ptk/archive/ptk.1995.12/0201.html or http://w4.lns.cornell.edu/~pvhp/ptk/etc/FileDialog.pm Harry Bochner chimed in with SaveAs.pm. It is available from: http://w4.lns.cornell.edu/~pvhp/ptk/etc/SaveAs.pm In general, if there is a feature that you want missing from one of these, or some behaviour that you would like to see modified then by all means cp the source code to your area and start hacking ;-) ______________________________________________________________________ 16.3. Is there a color editor? There is. Please see perldoc ColorEditor.pm or run the Tk/demos/color_editor demo script for more information. ______________________________________________________________________ 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 As well as from the Contrib/ sub-directory of your perl/Tk build directory. ______________________________________________________________________ 16.5. Is there something equivalent to tkerror? Yes there is. Please see the Tk/ErrorDialog.pm module for further information. ______________________________________________________________________ 16.6. Are there Tables? There are least two: Nick's Table ------------ Nick Ing-Simmons has distributed his own Table widget package with Tk-b9.01 (and higher). It is used through a use TK::Table; and $top->Table(); calls. A rather detailed demo of this widget/geometry manager's capabilities can be found in the table_demo script (in your Tk-b9.01/ build directory). There is also pod in the perl5/Tk/Table.pm file. You may also browse the perl Tk::Table man page on the web at http://w4.lns.cornell.edu/~pvhp/ptk/etc/Table.pm.html Guy Decoux's BLT_Table ---------------------- Guy Decoux <decoux@moulon.inra.fr> has ported the popular BLT_Table Tcl/Tk tabular geometry manager to perl/Tk. It was known to work with Tk-b8. You may obtain the latest version of it either from ftp://moulon.inra.fr/pub/pTk/ or from a CPAN site in the authors/id/GUYDX/ directory. You may also browse the perl BLT_Table man page on the web at http://w4.lns.cornell.edu/~pvhp/ptk/etc/Table.html ______________________________________________________________________ 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). ______________________________________________________________________ 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 :-) ______________________________________________________________________ 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 = $/; $/ = ''; } You can use this during code development to test out little snippets of code. It helps to be an accurate typist and the use strict; is optional here :-) 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 ______________________________________________________________________ 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 But it is recommended that you set you breakpoints carefully since just the calls to ManWindow->new require many steps. (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 And Gurusamy Sarathy notes that the patch to bring the debugger up to date is available at: 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). Note that a perl debugger may be invoked within your script with a line like: $ENV{'PERL5DB'} = 'BEGIN { require Tkperldb }'; See man perldebug(1) for more help. 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 Whereupon you must enter all the lines of a script including use Tk;. (Fancier file reads & evals are possible - but if you are getting that sophisticated why not create your own custom PERL5DB file?) When using perl -dwe 0 beware of the emacs like line editing under this debugger, and be forewarned that as soon as you type in the MainLoop; statement perl will no longer read from <STDIN>. 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 ;-) ______________________________________________________________________ 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] and address questions about SpecTcl to <spectcl@tcl.eng.sun.com>. 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. The URL for ui2perl should be something like: ftp://susan.logware.de/pub/incoming/ui2perl*.tar.gz Somewhat more removed from SpecTcl there is also SWIG. ______________________________________________________________________ 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/ as well as the web site at: http://www.perl.com/perl/everything_to_know/ipc/index.html In addition to the usual perl IPC routines Tk allows (at least) three more special functions: fileevent (for handling I/O events), send (for inter-widget communication), and after (for time control like a sleep expressly for widgets). 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(?) ______________________________________________________________________ 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? To which Nick Ing-Simmons <nik@tiuk.ti.com> replied: 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 An example of how one might use such a script would be to create and monitor a file foo like so: echo Hello from foo! > foo tktail foo & echo \"A ship then new they built for him/of mithril and of elven glass\" --Bilbo \ >> foo ______________________________________________________________________ 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. ______________________________________________________________________ 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__ (Please note that a script like this is now distributed as "TickerTape" in your Tk*/Contrib/ directory.) ______________________________________________________________________ 18.4. How do I update widgets while waiting for other processes to complete? The short answer is either $widget -> update; or $widget -> DoOneEvent; Here is a script that makes use of the first of these methods. Note that instead of actually doing something useful the "long running process" is simply a call to the perl sleep() function for illustrative purposes: #!/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__ ______________________________________________________________________ 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; } ! } To which a part of Nick Ing-Simmons' response was: 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; }