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Use ">!" to overwrite $cache_file in case noclobber is set. 
When noclobber is set, zsh will not allow the use of ">" to overwrite
the contents of a file. Instead, it displays a "file exists" error.
By using ">!" instead, we tell zsh to overwrite the file without
complaining.

Keeps track of the last changed directory. When a new shell is created,
the last directory will be restored. Mimics how tabs works in many
terminal emulators.