It takes me about 10 runs to get a line of output without the grep. Sometimes less. Try it :) EDIT: test.sh: for i in {1..1000} do ps | grep grep | wc

It takes me about 10 runs to get a line of output without the grep. Sometimes less. Try it :) EDIT: test.sh: for i in {1..1000} do ps | grep grep | wc -l done ./test.sh | sort | uniq -c 13 0 987 1 Which would indeed suggest 1.3%. Likely dependent on how quickly you're running it, if it's in memory already etc etc