Generate the page

The folder is back. ~/projects/first-site/index.html is still there from Unit 1. Open a terminal. Stand in the folder and print the file.

cd ~/projects/first-site
cat index.html

That is the page you typed. Now stop typing it. A page you type once is a page you retype after every wipe. You already rebuilt the folder from the keyboard. The page should be rebuilt the same way. The shell can write the bytes for you.

A program that prints text sends that text to stdout. Stdout is the stream that lands in your terminal unless you send it somewhere else. echo writes its argument to stdout, then stops.

Type this, then press Enter.

echo '<h1>Ground Zero</h1>' > ~/projects/first-site/index.html

echo would have printed that heading. The > sent the heading to the file instead. Single quotes keep the tags as text. The shell does not try to read them as markup.

> wipes first, then writes. Wipe means: empty the file, then put the new text in. Whatever you typed last unit is gone.

Print the file.

cat index.html

You should see only the heading. The old page is not sitting in a bin. The bytes were replaced. That is why > is the start of a generated file, not a way to add a line.

>> appends. Append means: add to the end, and leave what was already there.

echo '<p>Generated.</p>' >> ~/projects/first-site/index.html

Print it again.

cat index.html

Two lines. The heading from >, then the paragraph from >>. You did not type those tags into an editor. The shell generated them. Run the same two commands tomorrow and you get the same file. That is the point of generating, not typing.

Run the first echo with > again and the paragraph vanishes. Wipe, then write. That is the whole difference. Use > once, at the start. Use >> for every line after that. Swap them and you either wipe the page or append to yesterday’s markup.

A pipe (|) hands one program’s stdout to the next program as input. The next program reads what this one printed. Nothing extra is written to disk. That is the other fork from stdout. > puts the printout in a file. | hands the printout to another program. Both steal the text from the screen. Only > leaves a file behind.

ls ~/projects | wc -l

ls lists names. wc -l counts lines. The | means: do not print the listing; give it to wc.

When wc -l is given a file, the shape is a count and a name.

7 /etc/hosts

That seven is a capture of /etc/hosts, not a number for your folder. Your ls count is yours. Read the number your shell prints. Do not copy the seven.

A pipe can have a second stage. grep is one you will meet later. Given one file it prints line:text. Given a directory it prints path:line:text. You do not need grep to build this page. The pipe you just ran is enough: list, then count.

If a line on disk needs a small edit, open an editor. Check you have one first.

which nano

A path means nano is on this machine. Nano is a small text editor. Ubuntu and Fedora ship it by default.

On a Mac. Do not assume nano is there. Trust which nano, not a memory of older Macs.

On Windows / WSL. Run which nano here too. Do not assume the name is present.

Edit in place, or leave.

nano index.html — Ctrl-O writes the file, Ctrl-X leaves.

If you land in vim instead, you are in a full-screen editor that swallows ordinary keys. Press Esc, type :q!, then Enter. That leaves without saving.

command not found after a name means that name is not on your path. People read that as “not installed”. Either way, you cannot run it until which prints a path.

You do not need nano for this page. The two echo lines already built it. Nano is the escape hatch for a typo already on disk. The page itself should stay generated. If you rebuild the folder later, you rebuild the page with echo, not with the mouse.

Print what you made.

cat index.html

Two lines. Generated bytes. Same path as Unit 1. Different origin. Last unit the file existed because you typed it. Now it exists because the shell wrote it.

The folder is rebuilt from the keyboard. The page is generated, not mouse-typed. Next you look at the machine itself — the box that holds this file.

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