CT-152 Project #1 Directory Navigation General A directory is like a “folder” (in Windows). The general directory structure on all UNIX systems is the same. Within this directory structure are directories for users. Within these directories, the users can create further directories. Users can also navigate to their own directories or to other users’ directories. 1. General Directory Structure When you log-in to a UNIX system, any file that you create is in your “home” directory. To find-out what this home directory is called, execute the command $ pwd (Do not type the ‘$’—it is a “prompt.”) The response should be something like the following /home/smith (The name “smith” should be replaced with your log-in username.) The way to visualize this directory structure is as follows: / /home /home/smith /home/jones The symbol “/“ corresponds to the top-level directory (of the entire computer or operating system). The symbol “/home“ corresponds to a sub-directory within the top-level directory. The symbol “/home/smith“ corresponds to a sub-directory within “/home“ the directory. You should be able to look at your “sibling” directories under “/home“ by executing the following commands: $ cd .. $ pwd go-up one directory level $ ls list the contents of the directory You should see a whole bunch of names (with numbers in some cases). Get a screenshot of this output and paste it into your project report. To go back to your original (“home”) directory execute the command $ cd $HOME or just $ cd or $ cd smith (where “smith” is replaced with your log-in username). Within your user directory, you may create files and sub-directories. 2. Creating Simple Files The quickest way to create a small, text file is to use the commands “cat” or “echo.” $ cat << xxx >> xyz Now is the time for all good men to come to the aid of their party. xxx A new file should exist called xyz that contains the text “Now is the time for all good men to come to the aid of their party.” To see if this file exists merely enter $ ls and you should see the response xyz To see the (text) contents of the file enter $ cat xyz You should see the response Now is the time for all good men to come to the aid of their party. Another way of creating a simple file (in one line) is to do the following: $ echo “Now is the time for all good men to come to the aid of their party.” >> xyz Create a few files “abc” and “def” and fill them with the text ‘abctext’ and ‘deftext’. Upon entering $ ls you should see the response xyz abc def Upon entering $ cat abc you should see the response abctext 3. Creating Subdirectories Suppose you wished to create a directory called “temp” (within your current directory). To do so, enter $ mkdir temp You may then go to this directory $ cd temp and create files there. Create the following file and directory hierarchy within your newly-created “temp” directory: smith temp temp1 abc1 def1 temp2 ghi1 abc2 temp3 def2 abc3 def3 ghi3 For each file, write-out the full directory “path,” e.g., /home/smith/temp/temp1/abc1. You may copy an entire “directory branch” using the following command: $ cp –r temp3 temp4 The “-r” option stands for “recursive”: it copies all sub-directories within the directory. What happens when you execute this command twice? (What is the directory tree under “temp4”?) You may “save” the entire directory tree into a single file called temp.tar by executing the following command (from the $HOME directory): $ tar cf temp.tar temp The command “tar” stands for “tape archive” (when archives were on magnetic tape). (Archives are like “.zip” files.) If you should “lose” your directory tree, you may restore it from the archive (temp.tar) using the following command $ tar xf temp.tar temp If you wish to just “look inside” the archive execute the command $ tar tf temp.tar temp (The options “c,” “x” and “t” stand for “create,” “extract” and “list.”) (We will cover more about this “archiving” in the next project.) 4. More File Information Go to your “home” directory (cd $HOME) and execute the following commands: $ ls you should see the responses temp Now enter $ ls -lart you should see a response that looks something like this: drwxr-xr-x 10 smith smith 4096 2011-08-23 10:00 temp This response is a “more complete listing” of the contents of your directory. The most interesting part of this listing are the letters “drwxr-xr-x.” These letters stand for “directory,” “read,” “write” and “execute.” These letters represent “permissions,” i.e., can you read this file, can you write this file and can you execute this file. You will notice that there are three “reads” and three “writes” (and, possibly, three “exccutes”). The first group of three corresponds to you, the creator or “user” of the file. The second group of three corresponds to a “group” of users (of which you are a member). One computer or operating system can have many “groups.” In this example, everyone in your group can “read” your file, but not “write” to your file. The last group of three letters is “others,” i.e., everyone on the system (in any “group”). (The system administrator can do “anything” with your files.) If you wish to change the read, write or execute “permissions,” use the command chmod. Suppose you wished to protect your file (or directory) from your (accidentally) overwriting this file. You would execute the command $ chmod –w temp If you wish your “group” to not read from the file, execute the command $ chmod g-r temp If you wish your “group” to read from the file and everyone else (“others”) to not read from the file, enter $ chmod g+r,o-r temp Important note: for someone to “read” your directory and its sub-directories, i.e., get istiings, the directory must have “read” and “execute” privileges. Tricky stuff: If you look at the letters in the “more complete listing” (e.g., drwxr-xr-x) each letter in rwxrwxrwx can be thought of as a binary digit. For example rwxr-xr-x can be thought of as 111101101. If we represent this binary number as a three octal-digit number we would have 755. You could quickly grant everyone read and execute privileges, grant all group members read and execute privileges and grant yourself full privileges by using the command $ chmod 755 temp Modify your “temp” directory tree so that everyone in your “group” can read your temp1, but no one (besides yourself) can read your temp2 sub-directory. Test-it out by having another member of your “group,” i.e., another member of your class, access your directory.
