The address of a file

Look at the address bar. The page is already open.

Copy what you see. On Linux it should be:

file:///home/you/projects/first-site/index.html

That string is this file’s address. An address is the written location of one file.

The bar shows three slashes because file:// sits against a path that starts with /. You will write that path three ways before you leave this page.

The first character

A path is the address of a file or a folder on the machine.

Look at the part after file://. It begins with /.

An absolute path starts with /. It is a route from the top of the machine. That top is root — the folder that contains every other folder.

If the first character is not /, the path is relative. A relative path starts from where you are standing.

/home/you/projects/first-site always names this folder. projects/first-site names a projects folder under wherever you are now.

Write the file’s absolute path:

/home/you/projects/first-site/index.html

That is the same place the browser already showed you. file:// is how the browser opened it. The path after those slashes is the address on disk.

Drop the first / and you get home/you/projects/first-site/index.html. That looks complete. It is not. It starts with h, so it is relative. It only names this file if you are already standing at root.

Three short names

You will not type the full path every time. Three marks stand in for pieces of it.

~ is home. Home is this account’s folder. On Linux that folder is /home/you. So the same file is:

~/projects/first-site/index.html

The shell is the program that reads what you type. It replaces ~ with home first. The result starts with /. Bare cd, with no folder after it, goes home too.

Look at the address bar again. Strip file://. Cover /home/you with your thumb. What remains is /projects/first-site/index.html. Put ~ in front of that remainder. You have just written the home form.

. is here. It names the folder you are standing in. From inside first-site, the page is:

./index.html

You do not name projects or home in that spelling. You are already inside the folder that holds the file, so the file’s name is enough. The . makes that starting point explicit.

.. is the folder above. From inside first-site, .. is projects. cd means change folder. From inside first-site, cd .. puts you in projects.

You can stack the mark. ../.. is two folders up.

From one folder above first-site, the same file is ../first-site/index.html. From two folders above, it is ../../projects/first-site/index.html. Same file. Different starting points.

The first-character rule still holds. ./index.html starts with ., so it is relative. ../first-site/index.html starts with . too. ~/projects/first-site starts with ~. The shell expands ~ to home, and that result is absolute.

A space will split a name

If a folder name has a space, an unquoted command treats it as two names. Keep this folder as first-site. If you must use a space, put quotes around the whole path.

Case is a trap

On Linux, Index.html and index.html are two files. Both can sit in one folder, with different contents.

Your page is index.html. Ask for Index.html and Linux looks for a different name. The letters look similar to you. To the machine they do not match.

On a Mac. APFS is the Mac filesystem. A filesystem is how the machine stores names and files. The default is case-insensitive: Index.html and index.html are the same file. It is also case-preserving: it remembers the capitals you typed, but a change of case does not make a new file. A site that works on a Mac as Index.html can 404 on Linux over that one letter. A 404 means the name was not found.

On Windows / WSL. The Linux filesystem is case-sensitive, like Linux. The Windows drive at /mnt/c is not. Keep the project in the Linux home, and type the name exactly.

Three ways, one file

Write the address now:

• from the top: /home/you/projects/first-site/index.html
• from home: ~/projects/first-site/index.html
• from inside the folder: ./index.html

The first character tells you which kind you wrote. / is from the top. ~ is from home. . is from here.

Keep the letters exact. The name is index.html, not Index.html.

You know where the file lives. Next you look at what is inside it.

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