Shell Programming and Scripting

echo "The current users logged in are:" && who | awk '{ p
rint $1 }' | sort -u

cat /etc/passwd | cut -d":" -f1 | egrep -v '(avahi|beagleindex|messagebus|news|ntp)' > allusers
# this line will cat /etc/passwd and will print the user names as in : 
user1
user2
etc... 
# Inside the parentheses there is a list of user names to be omitted - the system ones, like in my case : news, ntp, games, mail, etc. 
#You will need to modify that per your case. Then the output is being redirected to a file. 
# Here you can execute your piece of code : 
who | awk '{ print $1 }' | sort -u >> allusers
# This will print the list of active users, and will append this list to the original file, containing all users. 
#  Then, we use 'uniq -u' to print only the unique ones - meaning, those that aren't online. 
uniq -u allusers
# the list follows. HTH.

awk 'BEGIN{while("who"|getline)a[$1]}
!($1 in a){print $1}' FS=":" /etc/passwd

$ who | awk '{print $1}' >>file
 
$ egrep -vf file /etc/passwd | awk -F":" '($3 >= 500 && $3 < 65534) {print $1 }'