CHECK_strAlphaNum

Description: Checks if the input value is a string that contains only characters and digits and shuts down the application if not.
Parameter:

• val: Input value to check.
• maxlen: The maximal length of the the string or 0 if the string length doesn't matter.
• allowEmpty: Set to true if you want to allow empty strings.
• returnNoDie: Set to true if you want to return (instead of aborting the program) when an error in the input is found.

Returns:

• The input value if it contains only characters and digits or stops (or false, if $returnNoDie is true) the program on an error.