Check If A Variable Is Set/Empty In Bash
41 Checking If Variable Is Empty
How to check if variable is empty
5 Minute Lessons in Shell Script Programming: Variable Test Operators
shellscript how to check whether a variable is empty or not
How to check if a variable is set in Bash
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5 Minute Lessons in Shell Script Programming: Variable Test Operator ":?" (colon - question mark)
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operations on scalar variables in shell scripting | substring | length | check if variable exists