In the code for IPC::Open3, if you set the third (stderr) filehandle to 0, stderr will be sent to stdout

#my $pid = open3(\*WRITE, \*READ, \*ERROR,"bc"); 
my $pid = open3(\*WRITE, \*READ,0,"bc");
    #if \*ERROR is false, STDERR is sent to STDOUT
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Also in your code you have 2 while loops, one for $out and one for $err. You will be better off using IO::Select to read the filehandles, otherwise the first while loop will "block" unless it's properly constructed.