If you want to disable the Screensaver on your Mac, by using the Command Line Interface (CLI), then you can do the following:
Step 1 – See what is currently set
defaults read com.apple.screensaver
Step 2 – Set the idleTime
defaults -currentHost write com.apple.screensaver idleTime 0
Step 3 – (Optional) – Undo the change
defaults -currentHost delete com.apple.screensaver idleTime