G'day rjbuckley,

Welcome to the Monastery.

I've previously encountered the same issue as you with Tk::fileevent: when you've read everything from the filehandle, the GUI locks up. I don't know what's going on under the hood, so I can't provide an explanation of this behaviour; however, the general solution is to read from the filehandle until you get an undefined result and then delete the event handler:

$widget->fileevent($fh, readable => sub {
    if (defined(my $read = scalar <$fh>)) {
        # Do something with $read here
    }
    else {
        $widget->fileevent($fh, readable => '');
    }
});
[download]

Here's a somewhat more robust solution that:

• Provides both a Go and a Stop button.
• Disables the Go when running.
• Disables the Stop when not running.
• Changes the text on both those buttons providing primitive status feedback.

[I wanted something like this for a future project, so it's a prototype of sorts. I'll be extending it for my own needs. Feel free to use all, some or none of the features.]

#!/usr/bin/env perl

use strict;
use warnings;
use autodie qw{:all};

use Tk;

{
    my $mw = MainWindow::->new(-title => 'Test `nmap` with Tk::fileeve
+nt');

    my $ctrl_F = $mw->Frame()->pack(-side => 'bottom');
    my $cmd_F  = $mw->Frame()->pack(-side => 'top');
    my $text_F = $mw->Frame()->pack(-side => 'top', -fill => 'both', -
+expand => 1);

    my $gui_data = {
        start_button_text => get_start_button_text(),
        stop_button_text  => get_stop_button_text(),
        button_pack_opts  => [-side => 'left', -padx => 10],
    };

    $gui_data->{out_T} = $text_F->Scrolled('Text',
        -scrollbars => 'osoe', -wrap => 'none', -bg => '#ffffff'
    )->pack(-fill => 'both', -expand => 1);
    sub get_button_width ();
    $gui_data->{start_B} = $cmd_F->Button(
        -textvariable => \$gui_data->{start_button_text},
        -state => 'normal',
        -width => get_button_width(),
        -command => [\&start_nmap, \$mw, $gui_data],
    )->pack(@{$gui_data->{button_pack_opts}});
    $gui_data->{stop_B}  = $cmd_F->Button(
        -textvariable => \$gui_data->{stop_button_text},
        -state => 'disabled',
        -width => get_button_width(),
        -command => [\&stop_nmap, \$mw, $gui_data],
    )->pack(@{$gui_data->{button_pack_opts}});

    $ctrl_F->Button(-text => 'Exit', -command => sub { exit })->pack;
}

MainLoop;

{
    my $nmap_running; BEGIN { $nmap_running = 0 }

    {
        my ($nmap_pipe, $nmap_pid);

        sub start_nmap {
            my ($mw, $gui_data) = @_;

            $nmap_pid = open $nmap_pipe, '-|', 'nmap -A localhost';
            $$mw->fileevent($nmap_pipe, readable => sub {
                if (defined(my $read = scalar <$nmap_pipe>)) { 
                    $gui_data->{out_T}->insert(end => $read);
                    $gui_data->{out_T}->yview('end');
                }
                else {
                    stop_nmap($mw, $gui_data);
                }
            });
            $nmap_running = 1;
            @$gui_data{qw{start_button_text stop_button_text}}
                = (get_start_button_text(), get_stop_button_text());
            $gui_data->{start_B}->configure(-state => 'disabled');
            $gui_data->{stop_B}->configure(-state => 'normal');
        }

        sub stop_nmap {
            my ($mw, $gui_data) = @_;

            $$mw->fileevent($nmap_pipe, readable => '');
            kill INT => $nmap_pid if kill 0 => $nmap_pid;
            $nmap_running = 0;
            @$gui_data{qw{start_button_text stop_button_text}}
                = (get_start_button_text(), get_stop_button_text());
            $gui_data->{start_B}->configure(-state => 'normal');
            $gui_data->{stop_B}->configure(-state => 'disabled');
        }
    }

    {
        my (@start_button_texts, @stop_button_texts);
        BEGIN {
            @start_button_texts = ('Start `nmap`', '`nmap` running ...
+');
            @stop_button_texts = ('`nmap` not running', 'Stop `nmap`')
+;
        }

        sub get_start_button_text { $start_button_texts[$nmap_running]
+ }
        sub get_stop_button_text { $stop_button_texts[$nmap_running] }

        sub get_button_width () {
            length +(sort { length $b <=> length $a }
                        @start_button_texts, @stop_button_texts)[0];
        }
    }
}
[download]

Thanks Ken, your solution works.

Try this one. I don't have nmap so I used something else that would produce output.

#!/usr/bin/perl

# http://perlmonks.org/?node_id=1176994

use strict;
use warnings;
use Tk;
use Tk::IO;

my $tester;

my $mw = MainWindow->new;
my $b1 = $mw->Button(-text => 'Go', -command => \&go)->pack();
my $b2 = $mw->Button(-text => 'Exit', -command => sub{exit} )->pack();

my $text = $mw->Scrolled('Text',-scrollbars=>'e')->pack;

MainLoop;

sub go
  {
  $tester = Tk::IO->new(
    -linecommand => sub {$text->insert('end', shift()) },
    );
  $tester->exec('ls -l | head'); # command goes in here
  }
[download]

Thanks tybalt89, your solution worked

#!/usr/bin/perl
use warnings;
use strict;

use Tk;

my $mw = 'MainWindow'->new(-title => 'nmap');
my $b1 = $mw->Button(-text => 'Go', -command => \&go)->pack;
my $b2 = $mw->Button(-text => 'Exit', -command => \&Tk::exit)->pack;

my $text = $mw->Scrolled('Text', -scrollbars => 'e')->pack;
MainLoop();

sub go {
    open my $nmap, '-|', 'nmap -A localhost' or die $!;
    $text->fileevent($nmap, 'readable', sub {
        $text->insert(end => scalar <$nmap>);
    });
}
[download]

BTW, no need for sub {&go} etc. Lexical filehandles and 3-argument form of open exist for pipes, too.

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
[download]

Thanks Choroba, I tried your code and got the same result as when I attempted fileevent. After inserting the text, the gui freezes. Might be something about my build: Perl 5.022001 Tk 8.4 4.4.0-47-generic GNU/Linux Do you know anything about using pipes to get it done? Thanks, -rjb

Note that a filehandle may be "readable", but not have a complete line. This may cause a "hang" when reading with angle brackets.

#!/usr/bin/perl --
use threads stack_size => 4096;
use threads::shared;
use Thread::Queue;
use strict;
use warnings;

{
    my $qin  = Thread::Queue->new();
    my $qout = Thread::Queue->new();
    my $guithread  = threads->create( \&tkguithread, $qin, $qout );
    my $nmapthread = threads->create( \&nmapthread, $qin, $qout );
    $guithread->join;
}
exit;

sub tkguithread {
    my( $qin, $qout ) = @_;
    require Tk;
    my $mw = Tk::tkinit();
    my $b1 = $mw->Button(-text => 'Go', -command => sub {
        $qin->enqueue( 'localhost' );
    })->pack();
    my $b2 = $mw->Button(-text => 'Exit', -command => [ $mw, 'destroy'
+ ] )->pack();
    my $text = $mw->Scrolled('Text',-scrollbars=>'e')->pack;
    $mw->repeat(
        500, #ms
        [ \&appendFromQToText, $qout, $text ],
    );
    $mw->MainLoop;
    return;
}
sub appendFromQToText {
    my( $qout, $text ) = @_;
    for(1..5){
        if( defined(  my $line = $qout->dequeue_nb  )){
            $text->insert('end', $line );
        }
    }
    return;
}
sub Sleeps(){ 
    Time::HiRes::usleep( 33 * 1000 ); ## microseconds
}
sub nmapthread {
    my( $qin, $qout ) = @_;
    threads->detach();    ## can't join me :)
    
    while( 1 ) {
#~         if( defined( my $url = $qin->dequeue_nb  ) ) {
        if( defined( my $url = $qin->dequeue ) ) {
            nmap( $url, $qout );
        }
        Sleeps();
    }
    return;
}
sub nmap {
    my( $host , $qout ) = @_;
    $qout->enqueue("got nmap($host)\n");
    $host =~ s{[^a-zA-Z0-9.]}{}g;
    $host = 'localhost' if ! length $host;
#~     my $pid = open my($H), qq{nmap -A "$host" |};
    my $pid = open my($H), qq{echo faker "$host" |};
    $qout->enqueue("pid($pid) \$! @{[int$!]} $!\n");
    $qout->enqueue("eof @{[eof($H)]}\n");
    while(<$H>) {
        $qout->enqueue( "nmap($host) $_" );
    }
    close $H;
    return;
}
[download]