[Perl] solved: examples of IO::Pipe and IO:Handle

David Baird david.baird at homemail.com
Tue Oct 29 06:28:38 PST 2002

I found the solution to my problem in the IO::Handle::blocking funtion. Here
is a full example.
It was tested with ActiveState Perl 5.6.1 Build 633 on Windows 2000, with no
additional modules.
I am open to comments on my code.

David Baird

#!/usr/bin/perl -w

use strict;

# For a Tk dialog child with output from the parent process
use Tk;
use Tk::widgets;
use Tk::ROText;

# To create a pipe between parent and child
use IO::Pipe;
my $pipe = new IO::Pipe;

my ($pid, $win, $scroll);

# Create a child Tk dialog
if($pid = fork()) {
    # create a non-blocking reading end of the pipe

    # Create main window
    $win = MainWindow->new;
    # Add a Textbox and a Button to main window
    $scroll = $win->Scrolled(qw/ROText  -height 10  -width 10  -scrollbars
se  -wrap none/)
        ->pack(qw/-fill both  -side right  -expand y  -padx 3/);
    $win->Button(-text => 'Quit', -command => [$win => 'destroy'])

    # upon focus, immediately process incoming characters
    $win->bind('<FocusIn>', sub {
                    my $char;
                    for ($char = ''; $char ne '~'; $char = $pipe->getc()) {
                        if ($char ne '') {
                            $scroll->insert('end', $char);
                        updateWidgets $win;
                    # the exit character is a '~' which will destroy the
    # Spin the message loop

# Here is the parent, which creates a writer end of the pipe
# and flushes every character

# Send a number every second to the pipe (the child dialog) and
# print an interesting message to the standard output
for (my $i = 19; $i >= 0; $i -= 1) {
    $pipe->print($i . ' ');
    print "value is $i\n";
    $pipe->print("\n") if ($i % 10 == 0);

# The end, bye bye
print "Goodbye\n";

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