Naming variables

The following rules apply to variables names 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 $(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: \   /   :   *   ?   " (  <   >   |