Files and directories

Last updated on 2026-10-27 | Edit this page

Estimated time: 35 minutes

Overview

Questions

  • How do you see the directory you are in, and how do you make a directory on scratch?
  • After mv, what does ls show?
  • What does rmdir print when the directory is not empty?

Objectives

  • Run pwd, mkdir -p, cd, and ls so an empty scratch directory prints nothing.
  • Create a file, show it with cat, copy it, and rename it so ls shows only the new name.
  • Remove an empty directory with rmdir, read the error on a non-empty directory, and remove it after emptying it.

The shell starts in home

Right after SSH, the current directory is your home directory. pwd prints that path. On Snellius it is /home/$USER. cd with no argument returns there from anywhere. ls prints the names in the current directory. An empty directory prints nothing. That empty print is success, not an error.

The scratch directory in the first task is not home. On Snellius it is /scratch-shared/$USER. mkdir -p creates it, and a second run does not fail if it is already there. The course cluster has no /scratch-shared. The tab names the scratch path you do have. Make your directory under that path. The pwd and ls checks are the same: ls of a new directory prints nothing.

Caution

Login node

pwd, mkdir, and cat of one small file are what the login node is for. Do not generate a thousand files in this shell, and do not run the print-n program here. Those belong in the last episode, and they go through sbatch.

Callout

Type along

Use the Snellius commands if your tab lists /scratch-shared. Otherwise use the scratch path in the tab, then the same pwd and ls.

Challenge

Task 1: make a scratch directory and show that it is empty

On Snellius:

BASH 

pwd
mkdir -p /scratch-shared/$USER
cd /scratch-shared/$USER
ls
pwd
cd
pwd

On the course cluster, /scratch-shared is not there. The tab names the scratch path. Create your directory under that path, cd into it, and run the same ls and pwd. Then cd with no argument.

pwd starts as /home/<your-login>.

mkdir -p creates the directory. On Snellius the path is /scratch-shared/$USER. On the course cluster it is a directory under the scratch path in the tab, not under /scratch-shared.

After cd into that directory, pwd prints it. ls prints nothing. No names, and no error, means the directory is empty.

cd with no argument returns to home. pwd prints /home/<your-login> again.

A file you can show, copy, and rename

touch creates an empty file. An editor such as nano or vim puts text in it. cat prints the file. printf is a way to put one known line in the file without an interactive editor, so the later cat has an answer you can check.

cp copies. The original stays. mv changes the name. After mv, ls of that directory shows the new name and does not show the old name.

Challenge

Task 2: copy, then rename

Start in home. On Snellius the scratch directory is /scratch-shared/$USER. On the course cluster, use the directory you created under the scratch path in the tab. The commands below say SCRATCH. Set it to that directory before you copy.

BASH 

cd
SCRATCH=/scratch-shared/$USER
printf 'one line\n' > notes.txt
cat notes.txt
mkdir -p "$SCRATCH"
cp notes.txt "$SCRATCH/notes.txt"
ls "$SCRATCH"
mv "$SCRATCH/notes.txt" "$SCRATCH/notes-kept.txt"
ls "$SCRATCH"
ls notes.txt

On the course cluster, set SCRATCH to the directory you created under the scratch path in the tab. Do not use /scratch-shared/$USER there.

cat prints:

one line

The first ls of the scratch directory prints notes.txt.

The ls after mv prints notes-kept.txt and does not print notes.txt. The new name is the only name in that directory.

The last ls notes.txt still finds the original in home. cp left it there. mv renamed only the copy.

Directories, empty and not

mkdir creates a directory. cd enters it. rmdir removes a directory only when it is empty. That limit is useful. rmdir will not delete a tree of files because you pointed it at the wrong place.

If the directory still has a file, rmdir prints an error and leaves the directory in place. Remove the file, then run rmdir again.

Challenge

Task 3: an empty directory

Run this in home.

BASH 

cd
mkdir demo-dir
cd demo-dir
pwd
ls
cd
rmdir demo-dir
ls

pwd inside demo-dir ends in /demo-dir. ls there prints nothing.

After cd back to home, rmdir demo-dir removes it because it is empty. The following ls does not list demo-dir.

Challenge

Task 3 continued: rmdir refuses a file

BASH 

cd
mkdir demo-dir
cd demo-dir
touch keep.txt
cd ..
rmdir demo-dir
rm demo-dir/keep.txt
rmdir demo-dir
ls

What does the first rmdir print, and what is true after the second?

The first rmdir fails. The message is:

rmdir: failed to remove 'demo-dir': Directory not empty

demo-dir is still there, and keep.txt is still inside it. rmdir did not delete the file.

rm demo-dir/keep.txt empties the directory. The second rmdir then succeeds. ls in home does not list demo-dir.

Key Points
  • pwd prints the current directory. A new shell starts in home.
  • mkdir -p /scratch-shared/$USER is the Snellius scratch directory. The course cluster uses the path in the tab.
  • ls of an empty directory prints nothing.
  • After mv, ls shows the new name only. cp leaves the original.
  • rmdir removes an empty directory. On a non-empty directory it errors, and it succeeds after you empty it.