bash: Positional Parameters

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1 3.4.1 Positional Parameters
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1 A POSITIONAL PARAMETER is a parameter denoted by one or more digits,
1 other than the single digit '0'.  Positional parameters are assigned
1 from the shell's arguments when it is invoked, and may be reassigned
1 using the 'set' builtin command.  Positional parameter 'N' may be
1 referenced as '${N}', or as '$N' when 'N' consists of a single digit.
1 Positional parameters may not be assigned to with assignment statements.
11 The 'set' and 'shift' builtins are used to set and unset them (⇒
 Shell Builtin Commands).  The positional parameters are temporarily
1 replaced when a shell function is executed (⇒Shell Functions).
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1    When a positional parameter consisting of more than a single digit is
1 expanded, it must be enclosed in braces.
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