Ok, here you go, this works, tested on linux. It uses sysread to get the output, and it gets around the \r problem. 
#!/usr/bin/perl
use warnings;
use IPC::Open3;

#cdrecord sends a /r (no newline) to output status 
#so it is difficult to get output 

my $pid = open3(\*WRITE, \*READ,0,"/usr/bin/cdrecord -v -dummy -eject 
+dev=1,1,0  my.iso");
            #if \*ERROR is false, STDERR is sent to STDOUT  

while(1){

select(undef,undef,undef,.01);

 if( sysread \*READ,$output,1024 ){
     print "$output\n";
 }else{ print "finished\n"; exit; }

}

[download]
OUTPUT from my testing: 
Track 01:   89 of   97 MB written (fifo 100%) [buf  99%]  27.3x.
Track 01:   90 of   97 MB written (fifo 100%) [buf  99%]  26.5x.
Track 01:   91 of   97 MB written (fifo  98%) [buf  99%]  27.3x.
Track 01:   92 of   97 MB written (fifo 100%) [buf  99%]  26.6x.
Track 01:   93 of   97 MB written (fifo  98%) [buf  99%]  27.4x.
Track 01:   94 of   97 MB written (fifo 100%) [buf  99%]  26.6x.
Track 01:   95 of   97 MB written (fifo 100%) [buf  99%]  27.4x.
Track 01:   96 of   97 MB written (fifo 100%) [buf  99%]  28.3x.
Track 01:   97 of   97 MB written (fifo 100%) [buf  99%]  27.5x.

Track 01: Total bytes read/written: 102400000/102400000 (50000 sectors
+).

Writing  time:   42.959s
Average write speed  15.5x.
Min drive buffer fill was 99%
Fixating...

WARNING: Some drives don't like fixation in dummy mode.
Fixating time:   26.760s

/usr/bin/cdrecord: fifo had 1613 puts and 1613 gets.
/usr/bin/cdrecord: fifo was 0 times empty and 872 times full, min fill
+ was 85%.

finished

[download]
I'm not really a human, but I play one on earth. flash japh

In reply to Re: not waiting for external command to complete before getting the output by zentara
in thread not waiting for external command to complete before getting the output by Anonymous Monk

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