Procedure 21.1. Creating and Changing Directories

From your home directory create a subdirectory in /tmp:

1. Enter

   mkdir  /tmp/test

   mkdir stands for “make directory”. This command creates a new directory named test in the /tmp directory. In this case, you are using an absolute path to create the test directory.

2. To check what happened, now enter

   ls -l /tmp

   The new directory test should appear in the list of contents of the /tmp directory.

3. Switch to the newly created directory with

   cd /tmp/test

Procedure 21.2. Creating and Copying Files

Now create a new file in a subdirectory of your home directory and copy it to /tmp/test. Use a relative path for this task.

	Overwriting of Existing Files
Before copying, moving or renaming a file, check if your target directory already contains a file with the same name. If yes, consider changing one of the filenames or use cp or mv with options like -i, which will prompt before overwriting an existing file. Otherwise Bash will overwrite the existing file without confirmation.

1. To list the contents of your home directory, enter

   ls -l ~

   It should contain a subdirectory called Documents by default. If not, create this subdirectory with the mkdir command you already know:

   mkdir ~/Documents

2. To create a new, empty file named myfile.txt in the Documents directory, enter

   touch ~/Documents/myfile.txt

   Usually, the touch command updates the modification and access date for an existing file. If you use touch with a filename which does not exist in your target directory, it creates a new file.

3. Enter

   ls -l ~/Documents

   The new file should appear in the list of contents.

4. To copy the newly created file, enter

   cp ~/Documents/myfile.txt .

   Do not forget the dot at the end.

   This command tells Bash to go to your home directory and to copy myfile.txt from the Documents subdirectory to the current directory, /tmp/test, without changing the name of the file.

5. Check the result by entering

   ls -l

   The file myfile.txt should appear in the list of contents for /tmp/test.

Procedure 21.3. Renaming and Removing Files or Directories

Now suppose you want to rename myfile.txt into tuxfile.txt. Finally you decide to remove the renamed file and the test subdirectory.

1. To rename the file, enter

   mv myfile.txt tuxfile.txt

2. To check what happened, enter

   ls -l

   Instead of myfile.txt, tuxfile.txt should appear in the list of contents.

   mv stands for move and is used with two options: the first option specifies the source, the second option specifies the target of the operation. You can use mv either

   • to rename a file or a directory,

   • to move a file or directory to a new location or

   • to do both in one step.

3. Coming to the conclusion that you do not need the file any longer, you can delete it by entering

   rm tuxfile.txt 

   Bash deletes the file without any confirmation.

4. Move up one level with cd .. and check with

   ls -l test

   if the test directory is empty now.

5. If yes, you can remove the test directory by entering

   rmdir test

1. Enter su. You are prompted for the root password.

2. Enter the password. If you mistyped the root password, the shell displays a message. In this case, you have to re-enter su before retyping the password. If your password is correct, a hash symbol # appears at the end of the prompt, signaling that you are acting as root now.

3. Execute your task. For example, transfer ownership of a file to a new user which only root is allowed to do:

   chown wilber kde_quick.xml

4. After having completed your tasks as root, switch back to your normal user account. To do so, enter

   exit

   The hash symbol disappears and you are acting as “normal” user again.

Procedure 21.6. Using History and Completion

If you already did the example Section 21.3.1, “Examples for Working with Files and Directories” your shell buffer should be filled with commands which you can retrieve using the history function.

1. Press repeatedly until cd ~ appears.

2. Press to execute the command and to switch to your home directory.

   By default, your home directory contains two subdirectories starting with the same letter, Documents and Desktop.

3. Enter cd D and press .

   Nothing happens since Bash cannot identify to which one of the subdirectories you want to change.

4. Press again to see the list of possible choices:

   tux@knox:~> cd D Desktop/   Documents/ tux@knox:~> cd D

5. The prompt still shows your initial input. Type the next character of the subdirectory you want to go to and press again.

   Bash now completes the path.

6. You can now execute the command with .

Procedure 21.7. Using Wildcards

Now suppose that your home directory contains a number of files with various file extensions. It also holds several versions of one file which you saved under different filenames myfile1.txt, myfile2.txt etc. You want to search for certain files according to their properties.

1. First, create some test files in your home directory:

   1. Use the touch command to create several (empty) files with different file extensions, for example .pdf, .xml and .jpg.

      You can do this consecutively (do not forget to use the Bash history function) or with only one touch command: simply add several filenames separated by a space.

   2. Create at least two files that have the same file extension, for example .html.

   3. To create several “versions” of one file, enter

      touch myfile{1..5}.txt

      This command creates five consecutively numbered files:

      myfile1.txt,…,myfile5.txt

   4. List the contents of your home directory. It should look similar to this:

      -rw-r--r-- 1 tux users   0 2006-07-14 13:34 foo.xml
      -rw-r--r-- 1 tux users   0 2006-07-14 13:47 home.html
      -rw-r--r-- 1 tux users   0 2006-07-14 13:47 index.html
      -rw-r--r-- 1 tux users   0 2006-07-14 13:47 toc.html
      -rw-r--r-- 1 tux users   0 2006-07-14 13:34 manual.pdf
      -rw-r--r-- 1 tux users   0 2006-07-14 13:49 myfile1.txt
      -rw-r--r-- 1 tux users   0 2006-07-14 13:49 myfile2.txt
      -rw-r--r-- 1 tux users   0 2006-07-14 13:49 myfile3.txt
      -rw-r--r-- 1 tux users   0 2006-07-14 13:49 myfile4.txt
      -rw-r--r-- 1 tux users   0 2006-07-14 13:49 myfile5.txt
      -rw-r--r-- 1 tux users   0 2006-07-14 13:32 tux.png
             

2. With the help of wild cards, select certain subsets of the files according to various criteria:

   1. To list all files with the .html extension, enter

       ls -l *.html

   2. To list all “versions” of myfile.txt, enter

      ls -l myfile?.txt

      Note that you can only use the ? wild card here because the numbering of the files is single-digit. As soon as you have a file named myfile10.txt you must to use the * wild card to view all versions of myfile.txt (or add another question mark, so your string looks like myfile??.txt).

   3. To remove, for example, version 1-3 and version 5 of myfile.txt, enter

      rm myfile[1-3,5].txt

   4. Check the result with

      ls -l

      Of all myfile.txt versions only myfile4.txt should be left.

	Display of Keys
In the following, find several commands that you can enter in vi by just pressing keys. These appear in uppercase as on a keyboard. If you need to enter a key in uppercase, this is stated explicitly by showing a key combination including the key.

1. To create and open a new file with vi, enter

   vi textfile.txt

   By default, vi opens in command mode in which you cannot enter text.

2. Press I to switch to insert mode. The bottom line changes and indicates that you now can insert text.

3. Write some sentences. If you want to insert a new line, first press to switch back to command mode. Press O to insert a new line and to switch to insert mode again.

4. In the insert mode, you can edit the text with the arrow keys and with .

5. To leave vi, press to switch to command mode again. Then press : which takes you to the extended mode. The bottom line now shows a colon.

6. To leave vi and save your changes, type wq (w for write; q for quit) and press . If you want to save the file under a different name, type w filename and press .

   To leave vi without saving, type q! instead and press .

The KDE and GNOME desktops store user-specific application data in hidden directories, for example .kde and .gnome.

1. To locate these directories on your computer, enter

   locate .kde

   if you have installed KDE desktop or

   locate .gnome

   if you have installed GNOME desktop.

   You will see that locate displays all file names in the database that contain the string .kde or .gnome anywhere. To learn how to modify this behavior refer to the man page of locate.

2. To search your home directory for all occurrences of filenames that contain the file extension .txt, use

   find ~ -name '*.txt' -print

3. To search a directory (in this case, your home directory) for all occurrences of files which contain, for example, the word music, enter

   grep music ~/*

   Note that grep is case-sensitive— unless you use it with the -i option. With the command above you will not find any files containing Music.

   If you want to use a search string which consists of more than one word, enclose the string in double quotation marks, for example:

   grep "music is great" ~/*

1. To write the output of a command like ls to a file, enter

   ls -l > filelist.txt

   This creates a file named filelist.txt that contains the list of contents of your current directory as generated by the ls command.

   However, if a file named filelist.txt already exists, this command overwrites the existing file. To prevent this, use >> instead of >. Entering

   ls -l >> filelist.txt 

   simply appends the output of the ls command to an already existing file named filelist.txt. If the file does not exist, it is created.

2. Redirections also works the other way round. Instead of using the standard input from the keyboard for a command, you can use a file as input:

   sort < filelist.txt

   This will force the sort command to get its input from the contents of filelist.txt. The result is shown on the screen. Of course, you can also write the result into another file, using a combination of redirections:

   sort  < filelist.txt > sorted_filelist.txt

3. If a command generates a lengthy output, like ls -l may do, it may be useful to pipe the output to a viewer like less to be able to scroll through the pages. To do so, enter

   ls -l | less

   The list of contents of the current directory is shown in less.

   The pipe is also often used in combination with the grep command in order to search for a certain string in the output of another command. For example, if you want to view a list of files in a directory which are owned by the user tux, enter

   ls -l | grep tux