(Updated: Something bad happened to the code portion during cut-and-paste to the site. This is now fixed.)

Here's a quick bit of code that provides a simple, object-oriented way to draw progress bars. To use it, just create a progress bar like so:

    my $bar = ProgressBar->new( width => 40 );
[download]

(Here, our bar will be 40 characters wide.) Then, to draw the bar, just pass in the current count of completed tasks and the total number of tasks:

    $bar->draw( 3, 10 );
[download]

So, in the above example, we have completed 3 of 10 tasks and the following would be drawn:

    ============                              30%
[download]

A couple of points:

• If the total number of tasks is fixed, you can provide it at the time you create the progress bar via the max_val parameter and omit it in calls to the draw() method.
• The code works properly for progress bars that go forward, backward, or both. (See the demo.)

Here's the code:

#!/usr/bin/perl -w

{
    # TGM 2004-10-05
    # Progress bar code

    package ProgressBar;
    use Class::Struct width => '$', portion => '$', max_val => '$';
    use List::Util qw( min );

    sub draw {
        local $| = 1;
        my ($self, $x, $max_val) = @_;
        $max_val ||= $self->max_val;
        my $old_portion = $self->portion || 0;
        my $new_portion = int( $self->width * $x / $max_val + 0.5 );
        print "\b" x ( 6 + $self->width
                       - min( $new_portion, $old_portion ) )
            if defined $self->portion;
        print "="  x ( $new_portion - $old_portion ),
              " "  x ( $self->width - $new_portion ),
              sprintf " %3d%% ", int( 100 * $x / $max_val + 0.5 );
        $self->portion( $new_portion );
    }

    1;
}

# DEMO

my $pb = ProgressBar->new( width => 40, max_val => 10 );

# show progress 0 to 100% and then back down to 0% again

do { $pb->draw( $_ )    ; sleep 1 } for 0 .. 10;
do { $pb->draw( 9 - $_ ); sleep 1 } for 0 ..  9;
print "\n";
[download]

Hope this helps.

Cheers,
Tom

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