Some messages and commands signal an alert in Terminal. In Terminal these alerts are known as “bells.” You can choose to have a visual alert that causes the Terminal window to blink, or an audible alert that causes an alert sound.
Choose Terminal > Preferences, and then click Settings.
Select a setting to modify in the Settings list, located on the left side of the Settings pane.
Click Advanced.
In the Bell section of the Advanced pane, select the type of alert you want Terminal to use.