[NMLUG] grep help

[Ed at Heron-ent.com (Ed Heron)]

  I'm writing a bash script that needs to check if a particular person is in 
a specific group.

  I'm using:

if grep "^${group}:.*[:,]${user}[,$]" /etc/group >/dev/null ; then echo 
"${user} is a member of ${group}" ; fi

  Unfortunately, if $user is last in the list it appears to be false.  If I 
`grep "^${group}:.*[:,]${user}$" /etc/group` it succeeds.

  I don't use many regexp, am I missing something?