Add yourself to any groups matching a regex pattern.

exp2-groupadd.sh

#!/bin/bash

#///////////////////////////////////////////////
# Expressions 2.0 - Group Auto Add
# by Alex Rydzak <adrydzak@syr.edu>
# purpose: add yourself to any Expressions 2.0 site groups you are not currently in.
#///////////////////////////////////////////////

echo "======================================="
echo "EXPRESSIONS 2.0 - Group Auto Add"
echo "======================================="

#get an array with current server website groups, all of which are expN (can be expNN or expNNN in the future)
exp_site_groups=( `cut -d':' -f1 /etc/group | grep exp'[0-9]\{1,\}'` )
#get count of items in exp_site_groups array
len_exp_site_groups=${#exp_site_groups[@]}

# get an array with current user's expN groups
users_groups=( `groups | grep -o exp'[0-9]\{1,\}'` )
#get count of items in users_groups array
len_users_groups=${#users_groups[@]}

#find out how many groups need to be added to the user
groups_diff=$((len_exp_site_groups-len_users_groups))

#echo out what we know so far...
echo "[*] Site groups discovered: --- $len_exp_site_groups"
echo "[*] User's current groups: ---- $len_users_groups"
echo "[*] Groups to add: ------------ $groups_diff"

#if the user has 0 groups that need to be added, we are done!
if [[ $groups_diff -eq "0" ]]; then
	echo "======================================="
	echo "[*] No groups to add! Exiting script..."
	exit
#if the user needs groups added, proceed...
else
	echo "======================================="
	#make a new array with the difference between the first two arrays we set
	to_add=( `echo ${exp_site_groups[@]} ${users_groups[@]} | tr ' ' '\n' | sort | uniq -u` )
	#we will now present what changes are happening to the end user to confirm
	for group in "${to_add[@]}"
	do
		echo "[*] Group to add for $USER: ${group}"
	done
	echo "======================================="
	#are we ok to make changes? y and Y will continue, n N or any other keystroke will exit
	read -p "[*] Add $USER to new groups? [y/n] " -n 1 -r
	if [[ $REPLY =~ ^[Yy]$ ]]
	then
		#let's add people to new groups
		echo
    	for group in "${to_add[@]}"
		do
			echo "[*] Adding group for $USER: ${group}"
			sudo usermod -a -G ${group} $USER
		done
	else
		#user cancelled the script, exit stage left
		echo
		echo "[*] User canceled! Exiting script..."
		exit
	fi
fi