Normal variable names are made up of a combination of letters, numbers and underscores, starting with a letter or an underscore. They are assigned a value with the syntax:
VARIABLE is the variable name. If the variable value needs to contain spaces then it should be enclosed in quotation marks. If single quote marks (') are used then the text is assigned literally to the variable. If double quote marks (“) are used, any variables within the text are first expanded in the manner explained below.
A variable name on a line by itself will unset that variable. So:
VARIABLE is unset.
When variables are being used in place of their value, they may be legally specified in any of ...