A user has written a few scripts for private use. Which of the following commands should be used so that no one else has execute permission?

To ensure that no one else has execute permission on the script while allowing the owner (user) to have execute permission, you should use the following command:

chmod u-rx script_file

This command removes the execute permission (-x) from the owner (u) of the script file, while leaving the permissions for others (a) unchanged.

The other options:

1. chmod a+x script_file: This adds execute permission for all users, including the owner, which is not what you want if you want to prevent others from executing the script.
2. chmod -R 755 script_file: This sets read, write, and execute permissions for the owner and read and execute permissions for others on the script file, which would grant execute permission to others.
3. chmod u+x script_file: This adds execute permission for the owner of the script file, but it doesn’t address the requirement of preventing others from having execute permission.