So I tossed this out here as an idea, but I would guess it has some holes in it. Will be interested to hear what others have done... .

Just a thought....

Thanks for the feedback! I appreciate the response...but I guess I was not clear with my desired outcome...I am using this: http://demos.telerik.com/kendo-ui/web/progressbar/index.html. Which will definitely handle everything for me as you suggested with ProgressBar (javascript library).

My main concern is actually with the mechanics of the loop that will supply the updated progress. I need to start execution, then (in a loop) periodically send the progress updates through a web socket message...until the program finishes.

I know I can kick off execution with open3 or run3, and then watch STDOUT from that program...but how do I break out of the loop? I guess I am not very familiar with how those libraries handle the file handles for STDOUT/ERR.

I wonder if something like this would work as intended?

...
run3 "somecommand -i somefile -o someoutputfile", $stdout, $stderr;
while(my $line = <$stdout>) {
  if($line =~ m/Progress: (\d+) lines processed/) {
    # Assume that $ws is the web socket object I have created and will
+ allow for the message to be sent...
    $ws->send($1);
  }
}
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This is getting me all sorts of frustrated. I have reverted to trying a simple test script and external program. The external program does nothing more than print a counter and then sleep for 1 second. I cannot seem to get its output while it is executing...Here is the code for both. Any help would be GREATLY appreciated...

the "child" program:

#!/usr/bin/env perl

use strict;
use warnings;
use 5.016;
use Carp qw(cluck carp croak);

my $c=1;
for(1..15) {
    say 'COUNT: '.$c;
    $c++;
    sleep(1);
}
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And here is the "parent" program...again, I am open to ANY solution that works. By "works", I mean that I need the output of the child program to be printed as it comes in. For the "real" program, I will need to send a web socket message every time output is received from the child program...the output will be a progress indicator (e.g. 10% complete, 15% complete, etc.).

First, with Capture::Tiny: (no dice)

#!/usr/bin/env perl

use strict;
use warnings;
use 5.016;
use Carp qw(cluck carp croak);
use Data::Dumper;
use Capture::Tiny ':all';

local $| = 1;

my $cmd = "/tempssd/bossert/bin/testchild.pl &";

my ($stdout, $stderr, @result) = tee { system($cmd); };

while (my $line = <$stdout>) {
    say 'GOT: '.$line;
    last if $line =~ m/^FINISHED/;
}
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Next, with IPC::Run: (Note, I get the STDOUT AFTER it runs...and it seems that the code ref for the stdout handling never fires.

#!/usr/bin/env perl

use strict;
use warnings;
use 5.016;
use Carp qw(cluck carp croak);
use Data::Dumper;
use IPC::Run qw(run);

local $| = 1;

my @cmd = ("/tempssd/bossert/bin/testchild.pl");

run \@cmd, '<', \undef,'>&',\&stdoutH or die "cat: $?";

sub stdoutH {
    my ($in) = @_;
    chomp $in;
    say 'STDOUT: '.$in;
}
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