CGI::ProgressBar - sub-class with a progress bar object


        use strict;
        use warnings;
        use CGI::ProgressBar qw/:standard/;
        $| = 1; # Do not buffer output
        print header,
                        -title=>'A Simple Example',
                                -src  => '', # You can override the bar style here
                                -code => '', # or inline, here.
                h1('A Simple Example'),
                p('This example will update a JS/CSS progress bar.'),
                progress_bar( -from=>1, -to=>100 );
        # We're set to go.
        for (1..10){
                print update_progress_bar;
                # Simulate being busy:
                sleep 1;
        # Now we're done, get rid of the bar:
        print hide_progress_bar;
        print p('All done.');
        print end_html;


This module provides a progress bar for web browsers, to keep end-users occupied when otherwise nothing would appear to be happening.

It aims to require that the recipient client have a minimum of JavaScript 1.0, HTML 4.0, ancd CSS/1, but this has yet to be tested.

All feedback would be most welcome. Address at the end of the POD.






The module sub-classes, providing three additional methods (or functions, depending on your taste), each of which are detailed below.

Simply replace your "use CGI qw//;" with "use CGI::ProgressBar qw//;".

Make sure you are aware of your output buffer size: $|=$smothingsmall.

Treat each new function as any other HTML-producing routine with the exception that the arguments should be supplied as in OOP form. In other words, the following are all the same:

        my $html = $query->progress_bar;
        my $html = progress_bar;
        my $html = progress_bar(from=>1, to=>10);
        my $html = $query->progress_bar(from=>1, to=>10);
        my $html = $query->progress_bar(-to=>10);

This will probably change if someone would like it to.


FUNCTION/METHOD progress_bar

Returns mark-up that instantiates a progress bar. Currently that is HTML and JS, but perhaps the JS ought to go into the head.

The progress bar itself is an object in this class, stored in the calling (CGI) object - specifically in the field progress_bar, which we create. (TODO: Make this field an array to allow multiple bars per page.)


Values which the progress bar spans. Defaults: 0, 100.


If set to vertical displays the bar as a strip down the screen; otherwise, places it across the screen.


The width and height of the progress bar, in pixels. Cannot accept percentages (yet). Defaults: 400, 20, unless you specify orientation as vertical, in which case this is reversed.


The number of blocks to appear in the progress bar. Default: 10. You probably want to link this to from and to or better still, leave it well alone: it may have been a mistake to even include it. steps is an alias for this attribute.


Supply this parameter with a true value to have a numerical display of progress. Default is not to display it.


Most HTML elements on the page have id attributes. These can be accessed through the layer_id field, which is a hash with the follwoing keys relating to the id value:


Custom CSS to be written inline (ugh) after any system CSS.


The form which contains everything we display.


The div containing everything we display.


This value is used as a prefixed for the id of each block of the bar, with the suffix being a number incremented from 1.


The digits being updated as the bar progresses, if the option is enabled.

FUNCTION/METHOD update_progress_bar

Updates the progress bar.

FUNCTION/METHOD hide_progress_bar

Hides the progress bar.


You can add CSS to be output into the page body (ugh) in the mycss field. Bear in mind that the width and height settings are programatically assigned.


A DIV containing the whole progress bar, including any accessories (such as the label). The only attribute used by this module is width, which is set dynamically. The rest is up to you. A good start is:

        padding:    2 px;
        border:     solid black 1px;
        text-align: center;
pblib_block_off, pblib_block_on

An individual block within the status bar. The following attributes are set dynamically: width, height, margin-right.


Formatting for the label text (part of which is actually an input type='text' element. border and text-align are used here, and the whole appears centred within a table.


One bar per page

This may change.

Parameter passing doesn't match

But it will in the next release if you ask me for it.

colors not implimented

I'd like to see here something like the Tk::ProgressBar::colors; not because I've ever used it, but because it might be cool.

Horizontal orientation only

You can get around this by adjusting the CSS, but you'd rather not. And even if you did, the use of -label might not look very nice unless you did something quite fancy. So the next version (or so) will support an -orientation option.

Inline CSS and JS

Because it's easiest for me. I suppose some kind of over-loading of the CGI::start_html would be possible, but then I'd have to check it, and maybe update it, every time was updated, which I don't fancy.


I'm not convinced it works yet, even in verion 3.15.

If anyone knows otherwise, please mail me: I have spent an hour on the below, and it seems that the hook is called more times than necessary....


The script has to both upload and process a file.

The hook script is called when the object is constructed, thus before any headers can be output. There the hook needs to output its own headers, and we only output headers for the 'select file' page when the hook has not been called.

The first tiem the hook is called, then, it outputs HTTP headers and begins the page. This is fine.

The next time it is called, it outputs the JS call to update the progress bar. This is fine.

The problem is that the hook seems to be called many more times than necessary.


        use warnings;
        use strict;

        use CGI::ProgressBar qw/:standard/;
        $| = 1; # Do not buffer output

        my $data;
        my $hook_called;
        my $cgi = CGI->new(\&bar_hook, $data);

        if (not $hook_called){
                print $cgi->header,
                $cgi->start_html( -title=>'A Simple Example', ),
                $cgi->h1('Simple Upload-hook Example');

        print $cgi->start_form( -enctype=>'application/x-www-form-urlencoded'),
                $cgi->filefield( 'uploaded_file'),

        if ($cgi->param('uploaded_file')){
                print 'uploaded_file: '.param('uploaded_file');

        sub bar_hook {
                my ($filename, $buffer, $bytes, $data) = @_;
                if (not $hook_called){
                        print header,
                        start_html( -title=>'Simple Upload-hook Example', ),
                                "Have to read <var>$ENV{CONTENT_LENGTH}</var> in blocks of <var>$bytes</var>, total blocks should be ",
                        progress_bar( -from=>1, -to=>($ENV{CONTENT_LENGTH}/$bytes), -debug=>1 );
                        $hook_called = 1;
                } else {
                        # Called every $bytes, I would have thought.
                        # But calls seem to go on much longer than $ENV{CONTENT_LENGTH} led me to believe they ought:
                        print update_progress_bar;
                        print "$ENV{CONTENT_LENGTH} ... $total_bytes ... $hook_called ... div="
                sleep 1;
                $hook_called += $total_bytes;

        print $cgi->hide_progress_bar;
        if ($hook_called){
                print p('All done after '.$hook_called.' calls');
        print $cgi->end_html;


Lee Goddard lgoddard -in- cpan -dat- org, cpan -ut- leegoddard -dut- net

Copyright (C) Lee Goddard, 2002, 2003, 2005. All Rights Reserved. This software is made available under the same terms as Perl itself. You may use and redistribute this software under the same terms as Perl itself.


HTML, CGI, progress bar, widget


perl. CGI, Tk::ProgressBar,


16 December 2005: Updated the styles and POD. Removed gap attribute.

25 March 2004: Updated the POD.

16 December 2005: Updated the default styles.

4 POD Errors

The following errors were encountered while parsing the POD:

Around line 274:

'=item' outside of any '=over'

Around line 390:

You forgot a '=back' before '=head1'

Around line 426:

You forgot a '=back' before '=head1'

Around line 452:

=back without =over