Arrays - Don't tread version 4 special - it has been around for a long time now

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http://wiki.bash-hackers.org – Purpose An array is a parameter that holds mappings from keys to values. Arrays are used to store a collection of parameters into a parameter. Arrays (in any programming language) are a useful and common composite data structure, and one of the most important scripting features in Bash and other shells.         (HowTos)