RE: capturing output from running process crashes gtk2

["Ratcliffe, Jeffrey (Peters)" <Jeffrey Ratcliffe External eads com>]

> It can not work this way. You need to start the sub process
> so that it writes to a pipe, then add the pipe's filehandle
> as an IO channel to the Glib/Gtk main loop. All processing
> of input from the pipe must be done from the IO channel's
> callback (careful here: you must only use non-blocking reads in
> this context). Rather advanced stuff, extra credit for
> getting the corner cases (e.g. killing the sub process) right.

Right. Almost there. The following script works, but gives me the warning "Name "main::WRITE" used only once: 
possible typo at ./test_dialog3 line 23." If I replace \*WRITE with 0, then I get the error message "open3: 
close(0) failed: Bad file descriptor at ./test_dialog3 line 23".

How do I write it so as to avoid the warning?

#!/usr/bin/perl -w

use strict;
use Gtk2 -init;
use IPC::Open3;

my $script = <<END;
#!/bin/bash
while [ 0 ]
do
 let ++page
 echo "Scanning page \$page" > "/dev/stderr"
 sleep 5
 echo "Scanned page \$page. (scanner status = 5)" > "/dev/stderr"
done
END

open SCRIPT, "> test_scan" or die "Can't open script";
print SCRIPT $script;
close SCRIPT;
chmod 0755, "test_scan"; # u+rwx,go+rw

my $pid = open3(\*WRITE, 0 ,\*ERROR, "./test_scan" );

my $dialog = Gtk2::Dialog->new ("Scanning...", undef,
                                'destroy-with-parent',
                                'gtk-cancel' => 'cancel');
my $label = Gtk2::Label->new ("Scanning...");
$dialog->vbox->add ($label);

# Ensure that the dialog box is destroyed when the user responds.
$dialog->signal_connect (response => sub { $_[0]->destroy;
                                           local $SIG{HUP} = 'IGNORE';
                                           kill HUP => $pid;
                                           Gtk2->main_quit;
                                         });
$dialog->show_all;

Glib::IO->add_watch(fileno(ERROR), 'in', sub {
                             my $line;
                             sysread ERROR, $line, 1024;
                             if ($line =~ /Scanning page ([0-9]*)/) {
                              $label->set_text("Scanning page $1...");
                             }
                             return 1;
                            });

Gtk2->main;

__END__