Unix::Passwd::File can be used to read and manipulate entries in Unix system
password files (/etc/passwd, /etc/group, /etc/group, /etc/gshadow) but can also
be told to search in custom location, for testing purposes).

This module uses a procedural (non-OO) interface. Each function in this module
open and read the passwd files once. Read-only functions like `list_users()` and
`get_max_gid()` open in read-only mode. Functions that might write to the files
like `add_user()` or `delete_group()` first lock `passwd.lock` file, open in
read+write mode and also read the files in the first pass, then seek to the
beginning and write back the files.

No caching is done so you should do your own if you need to.