The base of the filesystem in Unix-based operating systems (like Linux and Mac OS, which we will focus on in this class) is indicated with a single forward slash (/) and is known as the filesystem's root. The location of all files and folders can be written with a path (i.e., address) that starts at the root. Folders are hierarchical, so paths to highly nested folders will need to include all parent folders.
For instance, in the example above, the location of the Users folder can be written as /Users/, the location of the home directory for UserName can be be written as /Users/UserName/, and the location of their desktop folder can be written as /Users/UserName/Desktop/.
While the addresses for all files and folders can be written with paths that start at the root, it's sometimes cumbersome to do so. For instance, if you want to reference the parent folder of the folder you're in, it would be easier to provide the address that way (i.e., the parent of the folder I'm in), rather than write out the full path from the root. Paths that provide locations this way are known as relative paths. These are in contrast to absolute paths that always start at the root, /. Relative paths simply indicate where to look based on where you are. For instance, if your working directory is already /Users/UserName/, then you can reference the user's desktop folder by just writing Desktop. There are special symbols used to indicate the folder you're in (i.e., the current working directory) - . - and the parent folder of the current working directory - ... Another commonly used special symbol is ~, which indicates the home directory of the user.
Practice Exercise
If your current working directory is
/Users/UserName/, write the absolute paths for the directories referenced by the following relative paths.
Desktop
../Guest/
~/Library/
../../
Hidden Files and Folders
In Unix-based filesystems, you can keep some files and folders from showing up by default if you add a period, ., to the beginning of their names. These files are hidden. One common use for hidden files is to specify configuration settings for a program or system. These hidden files are usually stored in a user's home directory (e.g., /Users/UserName/). They can be revealed by listing a directory's contents using the -a flag - ls -a.