return its value. If it doesn't exist or is null, print the error message. If no error message is given, print parameter null or not set. Note: In a non-interac... t script. In an interactive shell, this will just print the error message. export foo="one" for i in foo... xists and isn't null, return its value; otherwise print varname: followed by message, and abort the curre... le doesn't exist or has a null value -- this will print the string to the standard error file handle and
