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.