Written 1 Sep 2026. This is a how-to, not a product card.

Reverse lines

After shuf, tac reverses lines so a practice list can be last line first. You don't need extra system software for this.

Mix lines mixed lines at random. Tonight you print a file last line first: tac. Tac reverses line order. Start with seq 1 5 | tac so a short number list is a safe peek.

You are still only practicing in home on the computer. The computer does not need extra system software, htop, Grafana, or a NAS for this one job.

Skip until SSH already works

SSH from the couch should already get you a prompt. SSH means type commands from your laptop, on the house network. If last letter first on each line is what you want, that is reverse characters. If mixed lines are what you want, that is mix lines. If a number list in order is what you want, that is print a number list.

What this is

tac reverses line order. Last line prints first. You type seq 1 5 | tac. Seq prints 1 through 5 once. Tac prints those lines last-first. Stick with that safe peek. You don't need extra system software for this.

It is not rev. Rev reverses characters on each line. It is not shuf. Shuf mixes lines at random. It is not seq as the job. Seq prints a number list once.

Practice tac in home

SSH into the computer.

Make sure home is where you sit:

pwd

You want a path that ends in your login name.

If the path is wrong, run this:

cd ~

Reverse a short number list, last line first:

seq 1 5 | tac

You want 5, then 4, then 3, then 2, then 1. Then the prompt back. That is enough for tonight. Practice only in home on the computer.

Debian and Ubuntu usually already have tac (coreutils). Don't make apt the job.

If tac is missing, install coreutils:

sudo apt install coreutils

Then stop. That apt line is not the lesson.

No files are required for this practice. If you made practice files anyway, throw them away with careful delete only. That is delete a file carefully. Skip rm -rf.

Useful extras, still home only

Optional extra: reverse a short word list:

printf 'pear\napple\nbanana\n' | tac

That peek prints banana, then apple, then pear. Don't make that line required. You can stay on seq 1 5 | tac.

Optional extra: tac, then head the first two lines:

seq 1 5 | tac | head -n 2

That peek shows only 5 then 4. Don't make head the job.

Skip huge dumps as this job. Skip tac piped into rm. Tac reverses lines. Rm deletes files. Don't mix those jobs. Skip files under /etc, whole /, SSH folders, USB sticks, and /srv. Practice only in home.

Skip screen, tmux, htop, Grafana, and a NAS. Keep SSH on the house network: keep the computer on the house network. Don't forward port 22.

What this is not

This is not rev. Rev reverses characters on each line. Tac reverses line order. That is reverse characters. It is not shuf. That is mix lines. It is not seq as the job. That is print a number list.

What next

Need last letter first on each line? Reverse characters. Need mixed lines? Mix lines.

Skip

Skip if SSH still fails. Finish SSH from the couch first.
Skip huge dumps as this job. Tonight: a short number list.
Skip tac piped into rm. Tac reverses lines. Don't mix delete into this drill.
Skip rev, shuf, and seq as this job. Those notes already exist.
Skip apt as this job. The coreutils aside is not the lesson.
Skip htop, Grafana, a NAS, files under /etc, and whole /.
Skip rm -rf. Careful delete only: delete a file carefully.
Skip opening SSH to the internet. That is keep the computer on the house network. Don't forward port 22.

Sources

Debian: tac(1). Ubuntu: tac(1). Official pages only. For reverse characters, see reverse characters. For mixed lines, see mix lines. For a number list, see print a number list. For the login, see SSH from the couch.

Also on this topic

SSH from the couchType commands on the computer from your laptop, on the house network. Password login first. Don't open this to the internet. Reverse charactersAfter tac, rev reverses characters on each line so a short word reads last letter first. You don't need extra system software for this. Mix linesAfter yes, shuf mixes lines at random so a practice list is not in file order. You don't need extra system software for this. Print a number listAfter tput, seq prints a number list in order so practice lines make sense. You don't need extra system software for this. Repeat a line until you stopAfter seq, yes repeats a line until you stop. Use head so the flood stops. You don't need extra system software for this. Put lines in orderAfter SSH works, sort puts lines in order so a mixed list is easier to scan. You don't need a file manager app for this. See the end of a fileAfter SSH works, tail prints the last lines of a file so a long file does not flood the window. You don't need a file viewer app for this. Read a file without opening the editorAfter SSH works, cat prints a file so you can read it without opening nano. Short files only. You don't need a file viewer app for this. Put a short line into a fileAfter SSH works, put one short line into a file with echo so you don't need to open nano. You don't need a file manager app for this. Send output into another commandAfter SSH works, a pipe sends output into another command so a long dump does not flood the window. You don't need extra system software for this. Delete a file carefullyAfter SSH works, delete one file with rm -i. Ask first. Skip rm -rf. You don't need a NAS for this. Turn off password login once the key worksAfter the laptop key login is boring, tell SSH to stop accepting the password. The key is how you get in. A keyboard on the computer is the backup now. Keep the computer on the house networkSSH and Pi-hole belong on the house network. Skip this if you never opened the router settings. Don't forward port 22.