You didn't actually say for certain whether "myprogram" also writes data to STDOUT as well as STDERR -- and if so, whether you want to keep both sets of data. Here are three scenarios, with suggestions for each (assuming a standard bourne-style shell is invoked by the "open" call):

• myprogram only writes to STDERR, never to stdout:

  open( $ResultPipe, "./myprogram 2>&1 |" );
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• myprogram writes to STDERR and STDOUT, but you want to ignore whatever gets written to stdout:

  open( $ResultPipe, "./myprogram 2>&1 > /dev/null |" );
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• myprogram writes to STDERR and STDOUT, and you want to capture both... well, one of them needs to be redirected to a file, and STDERR is the normal choice for that:

  open( $ResultPipe, "./myprogram 2> /tmp/err.$$ |" );
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  You really do not want to deal with them both together as a single stream (even if myprogram is designed so that all STDERR output lines match a consistent pattern), because there's a risk that a single line of STDOUT will be broken up by an intruding STDERR message.

You would need to read the part about redirection in the "sh" or "bash" man page to understand (or at least see examples of) the ordering of the redirection operators and their various meanings.