I think it depends on whether you want a console progressbar, or something requiring windows, like this example from BrowserUk. The nice thing about Tk is it will run on XWindows or MSWindows. Just put your merge code into the work sub, and figure out a way to compute $progress. You might want to make the progressbar wider for a 2GB merge. :-) 
#!/usr/bin/perl
use strict;
use threads qw[ async ];
use threads::shared;

our $WORKMAX ||= 1_000;

#by BrowserUk

## A shared var to communicate progess between work thread and TK
my $progress : shared = 0;

sub work {
    for my $item ( 0 .. $WORKMAX ) {
        { lock $progress; $progress = ( $item / $WORKMAX ) * 100; }
        select undef, undef, undef, 0.01;    ## do stuff that takes ti
+me
    }
}

threads->new( \&work )->detach;

## For lowest memory consumption require (not use)
## Tk::* after you've started the work thread.
require Tk::ProgressBar;

my $mw = MainWindow->new;
my $pb = $mw->ProgressBar()->pack();

my $repeat;
$repeat = $mw->repeat(
    100 => sub {
        print $progress;
        $repeat->cancel if $progress == 100;
        $pb->value($progress);
    }
);

$mw->MainLoop;

[download]
I'm not really a human, but I play one on earth. Cogito ergo sum a bum

In reply to Re: progress bar for a system command by zentara
in thread progress bar for a system command by xorl

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.