typeset:tldr:68c30

This command is using the typeset built-in command in a shell (such as bash) to declare and initialize an associative array. Below is an explanation of each part of the command:

• typeset: It is a built-in command used to declare or change the properties of variables.
• -A: This option specifies that the variable being declared will be an associative array. Associate arrays are arrays that use arbitrary strings as indices instead of numeric indices.
• ${variable}: This is the name of the variable (without the $) that will hold the associative array.
• =(: This assigns values to the array. The syntax =(:) initializes an associative array.
• ${[key_a]=item_a}: key_a is the index/key for the first element of the associative array, and item_a is its corresponding value.
• ${[key_b]=item_b}: key_b is the index/key for the second element, and item_b is its value.
• ${[key_c]=item_c}: key_c is the index/key for the third element, and item_c is its value.

So, by running this command, an associative array named ${variable} will be created, and it will have three elements with the following key-value pairs: key_a=item_a, key_b=item_b, and key_c=item_c.