The following rules apply to naming variables to pass signals:
•It can contain only alphanumeric characters.
•It cannot start with a number.
•You cannot put empty spaces in a variable name.
•If the variable is to be used in a C expression, it must be a legal C identifier.
•It is never a good idea to name a variable block -X, or a number, like 1 or 2 or 3. Naming a variable -X leads to confusion with the -x block. Naming a variable a number leads to confusion with the const block.
The following additional rules apply to naming variables that will expand into file names:
•It must be formatted as follows:
$(variable-name)
•It must adhere to the MS/DOS rules for device, directory, and file specifications. For example, a variable name cannot include the following characters: \ / : * ? " ( < > |