Can Linux do conditional judgment to insert the content at a certain line in Linux

Question

Can Linux do conditional judgment to insert the content at a certain line in Linux?

For example, I would like to add user "test" to /etc/sudoers to let it can switch to root:

 1 # 2 # This file MUST be edited with the 'visudo' command as root. 3 # 4 # Please consider adding local content in /etc/sudoers.d/ instead of 5 # directly modifying this file. 6 # 7 # See the man page for details on how to write a sudoers file. 8 # 9 Defaults env_reset 10 Defaults mail_badpass 11 Defaults secure_path="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/snap/bin" 12 13 # Host alias specification 14 15 # User alias specification 16 17 # Cmnd alias specification 18 19 # User privilege specification 20 root ALL=(ALL:ALL) ALL 21 22 # Members of the admin group may gain root privileges 23 %admin ALL=(ALL) ALL 24 25 # Allow members of group sudo to execute any command 26 %sudo ALL=(ALL:ALL) ALL 27 28 # See sudoers(5) for more information on "#include" directives: 29 30 #includedir /etc/sudoers.d 

I want my command to find row 20( if root ALL=(ALL:ALL) ALL ) then add the below content in row 21

test ALL=(ALL:ALL) ALL 

Can the Linux command do that or I can only do that by coding such as Perl or Python?

I am very new to Linux, any help is appreciated!

Answer 1

It doesn't matter where you add the line, sudo doesn't care about the order.

Just append it to the end:

echo 'test ALL=(ALL:ALL) ALL' | sudo tee -a /etc/sudoers 

Or, even better, use the include dir for it:

echo 'test ALL=(ALL:ALL) ALL' | sudo tee /etc/sudoers.d/test 

This way you don't have to manually update the sudoers file when it changes during package updates.