Unix lesson 1: Filesystems
This course will teach you the Unix operating system. So much of Unix deals with files as a basic unit for most transactions within the operating system: something as simple as editing a document, or ejecting a thumb drive, all deals with files. So let's see how they work.
A filesystem in Unix is a single entity. Unlike windows where there are different "drives", all "drives" are on the same filesystem in Unix. The filesystem is arranged like a tree of compartments full of files. Each one of these compartments is called a "directory". The base directory is called the "root", much like the roots of a tree. It is denoted by a single forward slash: / -- directories all fall underneath the root directory, to the right.
A location with all the directories from the root that point at the place you want to look, is called a "path". The path is constructed of the root, directories, and a filename (unless a directory is what you're looking for). The path is "case-sensitive", meaning that it treats upper-case letters (like "D") and lower-case letters (like "d") differently; meaning Desktop and desktop are two different directories or files. Here is an example:
/foo/bar/baz.txt
In this case, the initial forward slash (/) is the "root", foo is a "directory", bar is a "subdirectory" of foo, and baz.txt is the filename. As you can see, directories are separated by forward slashes.
Absolute and Relative Paths
In your shell (we'll talk about these later) or program, it will have an implicit "working directory". This is is the basis for all file operations, the directory your program is currently working with. It defaults to the root (/), but will frequently be another directory.
This path is where new files will be created from, as well as other directories. You can change this directory, or work against it, as we will see below.
An absolute path never takes the working directory into account. It always starts with the root, and always contains the full path. It is called "absolute" because it cannot be disputed based on the working directory.
A relative path, on the other hand, combines with the working directory to create a new path. It uses special syntax to assist with this:
..(two dots) means "up one directory".(one dot) means "within the current directory"
The special syntax is still delimited by forward slashes, just like a real directory.
Examples
This table represents a number of takes on the following working directory. It indicates if the original path is relative or absolute, and when it is relative, what the absolute path computed from the relative path looks like.
The working directory: /foo/bar
| Original Path | Absolute or Relative | Resolved Path |
|---|---|---|
/quux/baz/frobnik.txt | absolute | already resolved |
/foo/bar/loop.wav | absolute | already resolved |
/boo/hiss.foo | absolute | already resolved |
../quux/file.nod | relative | /foo/quux/file.nod |
./baz.html | relative | /foo/bar/baz.html |
../../other/file.txt | relative | /other/file.txt |
Assignment
Indicate whether the following paths:
- Are Absolute
- If relative, what the absolute path is
Working directory: /quux
/foo/bar/hi.txt/quux/bug/nope.foo../bar/baz.wav./foo.txt