Parameter Expansion

A parameter is a variable, one or more digits, or any of the characters *, @, #, ?, -, $, and !\. A variable is denoted by a vname. To create a variable whose vname contains a ., a variable whose vname consists of everything before the last . must already exist. A variable has a value and zero or more attributes. Variables can be assigned values and attributes by using the typeset special built-in command. The attributes supported by the shell are described later with the typeset special built-in command. Exported variables pass values and attributes to the environment.

The shell supports both indexed and associative arrays. An element of an array variable is referenced by a subscript. A subscript for an indexed array is ...

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