Lab3.sh

#!/bin/bash
# In order to delete all the mess created by this script
# just run it with "del" as a parameter
if [ "$1" != "del" ]; then
	# 1. List all users and their id's into work3.log
	for user in $(cat /etc/passwd | awk -F ":" '{print $1}'); do
		echo -e "user \"${user}\"\thas id $(id -u $user)" >> work3.log
	done
	# 2. Add the last password change date for root into the end of work3.log
	echo $(chage -l root | grep "Last" | awk -F ": " '{print $2}') >> work3.log
	# 3. Add the list of all groups in system divided by commas
	cat /etc/group | awk -F ":" '{printf("%s, ", $1)} END {print ""}' >> work3.log
	# 4. Make the file that will be created by default at a new user home folder
	echo "Be careful!" > /etc/skel/readme.txt
	# 5. Add a new user u1 with password 12345678
	useradd -m -p $(openssl passwd -1 -stdin <<< 12345678) u1
	# 6. Add a new group g1
	groupadd g1
	# 7. Add user u1 to group g1
	usermod -aG g1 u1
	# 8. Add the name, uid and groups of u1 to the end of work3.log
	echo -e "user \"u1\"\thas id $(id -u "u1")" >> work3.log
	echo "groups of $(groups u1)" >> work3.log
	# 9. Add $USER to g1 group
	usermod -aG g1 $USER
	# 10. Add all g1 users into the end of work3.log
	grep g1 /etc/group | awk -F ":" '{print $NF}' >> work3.log
	# 11. Run mc after login and die after logout for u1
	echo "/usr/bin/mc" >> /home/u1/.bash_profile
	echo "/usr/bin/pkill -KILL -u u1" >> /home/u1/.bash_profile
	# 12. Add a new user u2 with password 87654321
	useradd -m -p $(openssl passwd -1 -stdin <<< 87654321) u2
	# 13. Create /home/test13/ and copy work3.log into it
	mkdir /home/test13/
	cp work3.log /home/test13/work3-1.log
	cp work3.log /home/test13/work3-2.log
	# 14. only u1 and u2 can read /home/test13/, only u1 can write
	chown -R u1 /home/test13/
	chgrp -R u2 /home/test13/
	chmod 750 /home/test13/
	# 15. Make /home/test14/ with exclusive delete permission for u1
	mkdir /home/test14/
	chown u1 /home/test14/
	chgrp u2 /home/test14/
	chmod 1777 /home/test14/
	# 16. Copy nano to /home/test14/ and let anyone change files in /home/test13/ by it
	cp /bin/nano /home/test14/
	chown u1 /home/test14/nano
	chmod 4777 /home/test14/nano
	# 17. Add /home/test15/ and a secret_file in it, make this file invisible
	mkdir /home/test15/
	echo "Be careful!" > /home/test15/secret_file
	chmod a-r /home/test15/
else
	rm work3.log
	rm /etc/skel/readme.txt
	userdel u1
	userdel u2
	groupdel g1
	rm -r /home/u1
	rm -r /home/u2
	rm -r /home/test13/
	rm -r /home/test14/
	rm -r /home/test15/
fi

@AlexTalker, что к защите готовить?

К защите изучите как задавать shell по-умолчанию пользователю и для чего это может быть полезно.