SHELL

bash if user exists in a group then add

egrep -i "^groupname" /etc/group;
if [ $? -eq 0 ]; then
   echo "Group Exists"
else
   echo "Group does not exist -- Invalid Group name"
fi

bash if user exists in a group then add

egrep -i "^useraccount:" /etc/passwd;
if [ $? -eq 0 ]; then
   echo "User Exists"
else
   echo "User does not exist -- Invalid Username"
fi

bash if user exists in a group then add

#!/bin/bash
# init
USERID="$1"
#....
/bin/egrep  -i "^${USERID}:" /etc/passwd
if [ $? -eq 0 ]; then
   echo "User $USERID exists in /etc/passwd"
else 
   echo "User $USERID does not exists in /etc/passwd"
fi
# ....