Hello everybody.

I am writing code for a TK GUI, from which I am running a shell command and display its output on the window. I have also included a progressbar. The backbone of my code is shown below

#!/usr/bin/perl

use strict;
use Tk;
use Tk::ROText;
use Tk::ProgressBar;

my ($complete_steps,$steps,$progress,$pid) = (14,0,0,undef);

my $mw = new MainWindow;
my $button = $mw->Button(-text => 'Run', -command => sub{&run})->pack(
+);
my $pb = $mw->ProgressBar(-variable=>\$progress,-width => 20,-blocks=>
+100,-gap => 0)->pack(-fill => 'x', -expand => 1);
my $output = $mw->Scrolled('ROText', -scrollbars => 'osoe', '-wrap','n
+one')->pack(-anchor => 'nw', -fill => 'both', -expand => 1);

MainLoop();

sub run {
    my $cmd = "...";
    my ($flag,$cmd_handle);
    $pid = open ($cmd_handle, "$cmd 2>&1 |") or $flag = $!;
    unless ($flag){
        $mw->fileevent($cmd_handle,'readable', [\&working,$cmd_handle]
+);
    } else{}    
}

sub working {
    my ($cmd_handle) = @_;
    my $redline;

    my $stat = sysread $cmd_handle, $redline, 4096;
    unless ($stat == 0) {
        $output->insert('end', "$redline");$output->yview('end');
        &update_remaining($redline);
    } else {
        $mw->fileevent($cmd_handle ,'readable','');
        $steps = 0;
        $progress = 0;
    }
}

sub update_remaining {
    my ($redline) = @_;
    my @list= ($redline =~ /Now/g);
    $steps += scalar(@list);
    my $temp = 100 * ($steps/$complete_steps);
    $progress = $temp;
}

[download]

The problem is that while everything works ok and nothing blocks, perl seems to accepts the data from the pipe in batches (around 4000 characters at a time). When running the command directly in the shell, the output is gradually shown (line by line). I assume that "somewhere" between the command and the output window there is a buffer that I cannot locate and this messes up the progress bar smoothness.

I have checked that the number of bytes I use in the sysread doesn't play a role in that. So, any help is welcome.

Thanks in advance for your time.

In reply to Reading from a command pipe by DimosTsag

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