Modifying the file tree

Learning objectives

Questions

  • How do I create or remove files and directories?
  • How do I copy or rename files and directories? (You will see why these two operations are mentioned together shortly.)

Learning objectives

  • Learn how to create and remove files and directories.
  • Learn how to copy and rename/move files and directories.
  • Learn to avoid a few common pitfalls that could cause files to be deleted or overwritten by mistake.

Create and remove directories/files

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

Files

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

touch FILE

You can remove files with rm. You can use the flag/option -i to prompt before removing a file. Be aware that files removed with rm are deleted permanently—they generally cannot be restored (people have gotten lucky with system backup snapshots, but do not assume that those will be available).

Examples

Create a file called file.txt

touch file.txt

Remove the file file.txt

rm file.txt

Warning

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

Be extra careful using rm -rf with glob patterns (see Wild Cards under The File System )! It is strongly recommended that you always test a pattern with ls and check that the output is what you expect before using rm -rf on that pattern.

Directories

  • mkdir DIR: Creates a directory DIR
    • mkdir -p DIR/SUBDIR: creates a directory DIR with the subdirectory SUBDIR
  • rm -r DIR: Removes a directory DIR. The flag -r means recursively.
    • You can also add -f (meaning force). This means ignore nonexistent files and arguments, and never ask before deleting the target.
    • Again, 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

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 working directory
  • touch FILE: Create an empty file with the name FILE or update the timestamps of an existing file named FILE
  • rm FILE: Remove the file with the name FILE
  • pwd: print the current working directory path in full.

Creating directories, changing directories, removing directory and file, removing files by pattern

This example sequence will demonstrate some of the things we just learned, as well as the command cd and glob patterns from the previous section.

HINT: Code-along!

Create and remove directories:

[x_rebpi@tetralith1 ~]$ mkdir mytestdir
[x_rebpi@tetralith1 ~]$ cd mytestdir/
[x_rebpi@tetralith1 mytestdir]$ mkdir testdir1
[x_rebpi@tetralith1 mytestdir]$ mkdir testdir2
[x_rebpi@tetralith1 mytestdir]$ mkdir testdir3
[x_rebpi@tetralith1 mytestdir]$ ls
testdir1  testdir2  testdir3
[x_rebpi@tetralith1 mytestdir]$ rm -rf testdir3
[x_rebpi@tetralith1 mytestdir]$ ls
testdir1  testdir2

Create and remove files:

[x_rebpi@tetralith1 mytestdir]$ cd testdir1
[x_rebpi@tetralith1 testdir1]$ touch file1.txt
[x_rebpi@tetralith1 testdir1]$ touch file2.sh
[x_rebpi@tetralith1 testdir1]$ touch file3.c
[x_rebpi@tetralith1 testdir1]$ touch file4.dat
[x_rebpi@tetralith1 testdir1]$ rm file4.dat
[x_rebpi@tetralith3 testdir1]$ rm -i file3.c
rm: remove regular empty file 'file3.c'? y
[x_rebpi@tetralith3 testdir1]$ ls
file1.txt  file2.sh

Removing files by glob pattern (or why to always test a glob pattern with ls before using it with rm):

[x_rebpi@tetralith1 testdir1]$ cd ../testdir2
[x_rebpi@tetralith1 testdir2]$ touch meow.txt
[x_rebpi@tetralith1 testdir2]$ touch catsmeow1.dat
[x_rebpi@tetralith1 testdir2]$ touch homeowners_assoc.odt
[x_rebpi@tetralith1 testdir2]$ ls *meow*
catsmeow1.dat  homeowners_assoc.odt  meow.txt
[x_rebpi@tetralith1 testdir2]$ rm -r *meow{,1}.??t
[x_rebpi@tetralith1 testdir2]$ ls
homeowners_assoc.odt

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 myfile2.txt: make a copy of “myfile.txt” named “myfile2.txt”
  • cp myfile.txt DIR/: copy the file “myfile.txt” into the directory DIR
  • cp DIR1/ DIR2/: copy the directory DIR1 into the directory DIR2 (Note: only works if DIR1 contains no subdirectories)
  • 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 any existing file with the same name.

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

  1. 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:
   ```bash
   cd ..
   cp -r testdir1/testdir3 testdir2/
   ```

b) Copy from inside ``testdir1``
   ```bash
   cp -r testdir3 ../testdir2
   ```
  1. 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, and 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 DIR1 DIR2/: (note lack of forward slash after DIR1) moves directory DIR1 into directory DIR2/.
  • 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.

Tip

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

  1. Create three files (touch)
  2. Create a directory and then create a subdirectory of that directory (mkdir, cd)
  3. Create a file in the subdirectory (touch)
  4. Create another file inside the directory you created and then move it to the subdirectory you created (touch, cd, mv)
  5. Rename one of the directories (mv)
  6. Delete/remove a file (rm)
  7. Delete/remove the subdirectory (rm)
Solution - click to reveal
  1. I randomly name the files afile.txt, bfile.txt, cfile.txt
touch afile.txt
touch bfile.txt
touch cfile.txt
  1. I make the directory newdir and the subdirectory subdir
mkdir newdir
cd newdir
mkdir subdir
  1. I create a file named newfile.dat
cd subdir
touch newfile.dat
  1. I name the file secondfile.txt and move it into subdir
cd ..
touch secondfile.txt
mv secondfile.txt subdir
  1. I rename the first directory (top-level directory) I created, calling it fancydir
cd ..
mv newdir fancydir
  1. I remove the file afile.txt while working in the directory outside of fancydir (previously called newdir)
rm fancydir/afile.txt
  1. I remove the subdirectory subdir while outside the directory fancydir
rm -r fancydir/subdir

Tip

You can always check with pwd which directory you are working in!

Symbolic links

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

Symlinks are useful both for ease—you avoid using a long path each time you change to a directory, like your project directory—and to avoid changing hard links within other scripts or programs. It is good to avoid changing hardlinks 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 user x_rebpi, it would look like this:

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

Summary

  • You can create a directory named DIR with mkdir DIR
  • You can 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
  • Always test glob patterns with ls before using the same patterns with rm -r to remove files in bulk.