Shell Programming and Scripting

#!/usr/bin/env python
d={}
for line in open("/etc/group"):
    line=line.strip().split(":")
    users=line[3]
    if users:
        for u in users.split(","):
            d.setdefault(u,[])
            d[u].append(line[0])
for i,j in d.iteritems():
    print "%s is in groups: %s" %(i,j)

# ./test.py
daemon is in groups: ['bin']
user5 is in groups: ['dialout', 'video']
user2 is in groups: ['dialout', 'video']
user3 is in groups: ['dialout', 'video']
user1 is in groups: ['dialout', 'video']
nobody is in groups: ['nogroup']

logins -g <group name>

groupName="$1"

# Save some processing, no need to call getent so much.
#
groupEntry=$(getent group | grep "^${groupName}:")
if [ ! "$groupEntry" ]; then
        echo "Group $groupName does not exist." >&2
        exit 1
fi

# Note it IS possible that the same group is found in a local /etc/group
# as well as another source, you'll get two results.  We'll assume the
# first one wins.
#
groupId=$(echo "$groupEntry" | cut -d: -f3 | head -1)

# A username could be in a primary group and have that SAME primary
# group redundantly set as a secondary group.
#
passwdUser=$(getent passwd | cut -d: -f1,4 | grep ":${groupdId}$" | cut -d: -f1)
echo "${groupEntry},${passwdUser}" | cut -d: -f4 | tr ',' '\012' | sed '/^$/d' | sort -u