The given shell script is written in the Zsh shell syntax. It initializes a local array variable d with the expansion of a string. Let’s break it down step by step:

1. local d=: This line declares a local variable d. The local keyword is used to define variables with local scope, meaning they are only accessible within the current scope, such as within a function or a block of code.

2. "${(%):-%~}": This part of the script performs string expansion and substitution to populate the array d.

   • %~ is a special parameter expansion in Zsh that expands to the current working directory (tilde expansion).

   • (%): is another parameter expansion flag that performs splitting and globbing on the value obtained from %~. It splits the resulting string into separate elements based on the / delimiter and performs globbing (filename expansion) on each element.

     For example, if the current working directory is /path/to/some/directory, then %~ expands to /path/to/some/directory, and (%): splits it into individual components: path, to, some, and directory. If there are any glob patterns present, such as * or ?, they would be expanded as well.

3. ("${(@s[/])${(%):-%~}}"): This part surrounds the expanded string with parentheses to create an array and stores it in the variable d. The (@s[/]) syntax is an array flag in Zsh that splits the resulting string into separate elements based on the / delimiter. Each element represents a directory component obtained from the %~ expansion.

In summary, this script initializes the local array variable d with the directories present in the current working directory’s path. Each directory is stored as a separate element in the array d.