On 23/10/14 11:50, Nikos Andrikos wrote: > What is the proper way to check that each member of the $RET list is a > valid username and if not prompt the user to specify a new correct > list? This might be helpful: # usage: if is_username_valid root; then echo yes; fi is_username_valid () { getent passwd -- "$1" >/dev/null } Regards, S