In shell scripting, you can find the login names of all users on a system by examining the "/etc/passwd" file, which contains user account information. To print all user login names simultaneously, you can use the "cut" command in combination with other commands like "awk" or "cut" to extract the necessary information. For instance, running "cut -d: -f1 /etc/passwd" will display a list of all user login names in the system.