UNIX® Shells by Example, Third Edition

7.9. Arrays

Arrays in awk are called associative arrays because the subscripts can be either numbers or strings. The subscript is often called the key and is associated with the value assigned to the corresponding array element. The keys and values are stored internally in a table where a hashing algorithm is applied to the value of the key in question. Due to the techniques used for hashing, the array elements are not stored in a sequential order, and when the contents of the array are displayed, they may not be in the order you expected.

An array, like a variable, is created by using it, and awk can infer whether it is used to store numbers or strings. Array elements are initialized with numeric value zero and string value null, depending on ...