If you're trying to collect stats on the cp cmd, you can do it as 2 diff progs.
1st, start the gatherer prog (iostat etc) in the background eg
nohup ./gatherer.sh &
then run the cp script, then kill the gatherer (which will have shown it's pid when you started it).
Alternatively, you can embed the gatherer script invocation at the top of the cp script and use the $! var to get it's pid; see http://tldp.org/LDP/abs/html/x8280.html