Modifying the file tree¶

Learning objectives

Questions

How do create and remove files and directories?
How do I copy/rename files and directories?

Learning objectives

Learn how to navigate the Linux file system
Learn about files and directories
Learn about paths
Be able to create and delete files and directories, as well as rename and copy them

Create and remove directories/files¶

This section will show how to work with files and directories through command line interface.

Directories¶

mkdir DIR: Create a directory DIR
- mkdir -p DIR/SUBDIR: create a directory DIR with the subdirectory SUBDIR
rm -r DIR: Remove a directory DIR. The flag “-r” means recursively
- You can also add “-f”. This means ignore nonexistent files and arguments, and never prompt.
- You can add the option “-i”. This means it will prompt before every removal.

Examples, creating and removing directories

Create a directory called mynewdir

mkdir mynewdir

Create a directory called cooldir which has a subdirectory called fancydir

mkdir -p cooldir/fancydir

Remove the directory mynewdir

rm -r mynewdir

Files¶

To create files, you would normally use an editor (nano, vim, emacs, etc.), but it is also possible to create an empty file with the command touch.

touch FILE

You can remove files with rm. Again, you can use the flag/option -i to prompt before removing a file.

Warning

If you do not add the flag/option “-i” the file will be deleted without prompting. Be careful!

Examples

Create a file called file.txt

touch file.txt

Remove the file file.txt

rm file.txt

Examples¶

Reminder

mkdir DIR: Create a directory DIR
rm -rf DIR: Remove a directory DIR. The flag “-r” means recursively and “-f” means do so without asking for each file and subdirectory. Useful, but dangerous. Be careful!
cd: Go to your home directory ($HOME)
cd DIR: Change directory to DIR
cd ..: Change directory to the parent directory of the current directory
cd -: go back to the previous directory
touch FILE: create an empty file with the name FILE
rm FILE: remove the file with the name FILE
The command pwd tells you the current directory path.

Creating directories, changing directories, removing directory and file

This example will test some of the things we just learned, as well as the command cd from the previous section.

HINT: Code-along!

[x_birbr@tetralith1 ~]$ mkdir myowntestdir
[x_birbr@tetralith1 ~]$ cd myowntestdir/
[x_birbr@tetralith1 myowntestdir]$ mkdir testdir1
[x_birbr@tetralith1 myowntestdir]$ mkdir testdir2
[x_birbr@tetralith1 myowntestdir]$ mkdir testdir3
[x_birbr@tetralith1 myowntestdir]$ rm -rf testdir3
[x_birbr@tetralith1 myowntestdir]$ cd testdir1
[x_birbr@tetralith1 testdir1]$ touch file1.txt
[x_birbr@tetralith1 testdir1]$ touch file2.sh
[x_birbr@tetralith1 testdir1]$ touch file3.c
[x_birbr@tetralith1 testdir1]$ touch file4.dat
[x_birbr@tetralith1 testdir1]$ touch file5.txt
[x_birbr@tetralith1 testdir1]$ rm file5.txt
[x_birbr@tetralith1 testdir1]$
[x_birbr@tetralith1 testdir1]$ cd ..
[x_birbr@tetralith1 myowntestdir]$ cd testdir2/
[x_birbr@tetralith1 testdir2]$

Note

This was done on Tetralith. You will notice that only the current (subdir) is shown in the prompt. At some other centres all the (sub)dirs would be shown.

Example: HPC2N

b-an01 [~]$ cd mytestdir
b-an01 [~/mytestdir]$ cd testdir1
b-an01 [~/mytestdir/testdir1]$

cp - copy files/directories¶

This command is used to copy files or directories.

cp myfile.txt DIR/: copy the file “myfile.txt” to the directory DIR
cp DIR1/ DIR2/: copy the directory DIR1 into the directory DIR2 (Note: overwrites existing files with same name)
cp -R DIR1/ DIR2/: copy the directory DIR1 and all subdirectories into the directory DIR2.
cp -i file.txt DIR/: Interactive. It will ask before overwriting if there is a file with the same name.

Warning

If you do not add the option “-i” you risk overwriting an existing file, if it is named the same.

Code-along

Go to the directory mytestdir under exercises directory that you got from the downloaded tarball. This is how the structure looks:

folders of exercises directory structure

Change to the subdirectory:

cd exercises
cd mytestdir

2. Copy the file myfile.txt to the subdirectory testdir1:

cp myfile.txt testdir1

3. Create a new directory called testdir3 inside testdir1

cd testdir1
mkdir testdir3

4. Copy the new subdirectory testdir3 to the directory testdir2. Remember, “testdir2” is located outside “testdir1” and at the same “level”. This can be done in more than one way. Remember you need the option -r (for recursive) when copying directories: a) “Go up one” and then copy:

cd ..
cp -r testdir1/testdir3 testdir2/

b) Copy will standing inside testdir1

cp -r testdir3 ../testdir2

5. If you give the full path while copying, this can be done from anywhere.

mv - rename files/directories¶

The command mv is used to rename files and directories. It can also be used to move a file or directory to another location.

mv file1.txt file2.txt: renames file1.txt to file2.txt
mv DIR1/ DIR2/: renames directory DIR1 to directory DIR2/
mv file1.txt DIR1/: moves the file file1.txt into the directory DIR1/
mv -i file1.txt file2.txt: interactive. Asks before overwriting if there is already a file with the destination name.
mv -i DIR1/ DIR2/: interactive. Asks before overwriting if there is already a directory with that name.

Note

mv complains if there is already a file/directory with the new name. You can force the renaming with “-f” at the cost of the disappearence of the file that previously held the name.

Exercise¶

Exercise

Create three files (touch)
Create a directory and then create a subdirectory of that directory (mkdir, cd)
Create a file in the subdirectory (touch)
Create another file inside the directory you created and then move it to the subdirectory you created (touch, cd, mv)
Rename one of the directories (mv)
Delete/remove a file (rm)
Delete/remove the subdirectory (rm)

Solution - click to reveal

I am randomly naming the files afile.txt, bfile.txt, cfile.txt
```
touch afile.txt
touch bfile.txt
touch cfile.txt
```
I am naming the directory newdir and the subdirectory subdir

mkdir newdir
cd newdir
mkdir subdir

3. I am creating a file named newfile.dat

cd subdir
touch newfile.dat

4. I am naming the file secondfile.txt

cd ..
touch secondfile.txt
mv secondfile.txt subdir

5. I will rename the first directory (top-level directory) I created, calling it fancydir

cd ..
mv newdir fancydir

6. I will remove the file afile.txt while standing “above” the directory fancydir (previously called newdir)

rm fancydir/afile.txt

7. I am removing the subdirectory subdir while standing above the directory fancydir

rm -r fancydir/subdir

Tip

You can always check with pwd that you are standing in the directory you think you are!

Symbolic links¶

Symbolic links are also called soft links, or just symlinks. It is a pointer to another file or directory.

It is useful both for ease
- you avoid using a long path each time you change to a directory, like your project directory
- as well as to avoid changing hard links within other scripts or programs. This is good if you for instance install a program or use a script that assumes the library it uses is called libcoolness.a and not libcoolness.2.0.a. You can then just update the symlink instead of renaming the library or updating potentially many instances where it is mentioned in the program.

Command:

ln -s real-file-or-lib link-name

Example (on Tetralith)

ln -s /proj/linux-intro/users/MYUSERNAME $HOME/myproj

This creates a symbolic link named “myproj” in your home directory, pointing to the location /proj/linux-intro/users/MYUSERNAME. The directory “linux-intro” is the project storage directory for this course project. For me, this would look like this:

[x_birbr@tetralith1 ~]$ ls -l
total 2
lrwxrwxrwx 1 x_birbr x_birbr   31 Sep 11 12:01 myproj -> /proj/linux-intro/users/x_birbr
drwxrwxr-x 4 x_birbr x_birbr 4096 Sep 11 11:43 mytestdir

Keypoints

You create a directory named DIR with mkdir DIR
You remove a directory named DIR with rm -r DIR
You can create an (empty) file named FILE with touch FILE
You can remove a file named FILE with rm FILE
The command to copy files and directories is cp
The command to rename files and directories is mv
Symbolic links are pointers to another file or directory