0 stdin
1 stdout
2 stderr

stdout + stderr to /dev/null:  

> /dev/null 2>&1


stdout to /dev/null and stderr to file: 

>/dev/null 2>>/var/log/myerror
 

remove stderr only

2>/dev/null


grep -v on stderror

(command 2>&1 1>&3 | grep -v 'remove this error' 1>&2) 3>&1