Otherwise, substitute the null string. In conditional substitution, the shell does not evaluate the String variable until the shell uses this variable as a substituted string. When you run a shell procedure, the shell implicitly creates positional parameters that reference each word on the command line by its position on the command line. To refer to command line parameters numbered higher than 9, use the built-in shift command. You can reset the values of the positional parameters explicitly by using the built-in set command.
Positional parameters are global and can be passed to nested shell procedures.
File Name Substitution in the Bourne Shell Command parameters are often file names. You can automatically produce a list of file names as parameters on a command line. To do this, specify a character that the shell recognizes as a pattern-matching character. When a command includes such a character, the shell replaces it with the file names in a directory. The Bourne shell does not support file name expansion based on equivalence classification of characters.