You signed in with another tab or window. Reload to refresh your session.You signed out in another tab or window. Reload to refresh your session.You switched accounts on another tab or window. Reload to refresh your session.Dismiss alert
Using :? will cause the command to fail if the variable is null or unset. Similarly, you can use :- to set a default value if applicable.
In the case command substitution, assign to a variable first and then use :?. This is relevant even if the command seems simple and obviously correct, since forks and execs can fail due to external system limits and conditions, resulting in a blank substitution.
For more details about :? see the "Parameter Expansion" section of the Bash man page.