Math 171 Spring 2005, Lab 1

Due Thursday, January 20 11:59 P.M.

1. Overview
2. Using UNIX Commands
3. UNIX Command Summary
4. Assignment

Overview

This lab is intended to introduce you to the most commonly used UNIX commands and test your ability to use them. Each command is followed by a description of its purpose and examples of its usage.

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Using UNIX commands

• After you log in, locate the terminal icon near the bottom of the screen. Click this icon to start a shell. If this icon does not appear, you will need to enter the start menu (the RedHat button) and select "Run Program", then type "xterm".
• The UNIX shell reads commands from the keyboard and executes them. The shell signals that it is ready for additional commands by providing a prompt, a short string of characters usually ending with a #, $, :, or >.
• For each of the command descriptions that follows, example command usage is provided in a fixed-width font set off from the description by two blank lines. If you are not already familiar with UNIX, you should practice each command (with one exception) by typing in the examples and reading any output.
• The man command displays help on using each command. Type space to view additional pages of documentation, and type q when you are done reading. Read the documentation about the man command now:
  

  
  man man
  
  

• Many UNIX shell commands read from standard input and write to standard output. By default, standard input is whatever you type at the keyboard, and standard output is displayed on the screen.
• Most UNIX shell commands require one or more words to follow the command name. These words are called arguments and are used to specify the exact behavior of the command.
• The cat command is used to concatenate the files given as arguments (or standard input if no arguments are given). Note that concatenation means adding one file to the end of another. Since cat displays to standard output by default, you can use cat to display short textfiles to the screen. Practice using cat to display and combine the files /etc/fstab and /etc/hosts:
  

  
  cat /etc/fstab
  cat /etc/hosts
  cat /etc/fstab /etc/hosts
  
  

  You may also want to read the documentation for the cat command:
  

  
  man cat
  
  

• Since cat reads from standard input by default, running cat without any arguments will display whatever you type at the keyboard back to the screen (this is called echoing). Practice using cat this way and type CTRL-D (which we will abbreviate as ^D) to signal the end of standard input when you are finished:
  

  
  cat
  this is my input from the keyboard...
  ^D
  
  

• The sort command performs alphabetic sorting of standard input or the files given as arguments. Practice sorting the password file and compare with the unsorted version:
  

  
  sort /etc/passwd
  cat /etc/passwd
  
  

• UNIX shells provide two facilities for changing the behavior of standard input and output: redirection and pipes. The input redirection operator < is used to change standard input to a file rather than the keyboard. The output redirection operator > is used to change standard output to a file, which will be overwritten if it already exists. The output redirection operator >> is similar, but appends files instead of overwriting them. Lastly, a pipe | between two commands changes the standard output of the command on the left side of the pipe to the standard input of the command on the right side of the pipe. Practice combining two files and saving them to a third file, sorting/storing the output of cat, and viewing a file by redirecting standard input:
  

  
  cat /etc/fstab /etc/hosts > out1
  cat out1 | sort > out2
  cat < out2
  
  

• The current working directory is the default location for any files input or output by a shell command. Use pwd to display the current working directory. When you first log in to your account and open a terminal window, the current working directory will usually be set to a special directory called your home directory. Try displaying the name of your home directory now:
  

  
  pwd
  
  

  You can refer to your home directory with this longer name or by using the tilde (~) symbol, which the shell understands to be synonymous with your home directory. You may refer to another user's home directory using the tilde followed by their username. For example, my username is gbutler, so you can access my home directory using ~gbutler. Every directory is a subdirectory of (i.e. contained in) another directory called its parent directory. You can refer to the parent of the current working directory using two periods (..). The directory / is called the root directory and contains all other directories.
• The cd command is used to change the current working directory to the directory specified on the command line, or to your home directory if no argument is given. If you specify a directory beginning with a /, you must specify the full directory name. Otherwise, the directory you specify is assumed to be a subdirectory of the current working directory. Practice changing your directory to /etc three different ways and then back home again:
  

  
  cd /etc
  pwd
  cd
  pwd
  cd /
  pwd
  cd etc
  pwd
  cd ~
  pwd
  cd /bin
  pwd
  cd ..
  pwd
  cd etc
  pwd
  cd
  pwd
  
  

• The ls command is used to display information about the files given as arguments, or about the current working directory if no files are given. Use ls to display the contents of your home directory and /etc two different ways:
  

  
  cd
  ls
  ls /etc
  cd /etc
  ls ~
  ls
  cd
  
  

  In addition to file names, ls may take one ore more arguments beginning with a dash that modify the information provided (these are called flags). A few of these are listed below:

  Flag	Purpose
  -l	Long output format (extra information)
  -R	Recursive listing (list directory and all its subdirectories)
  -d	List directory only, not its contents
  -a	List all files, even if they are hidden
  -F	Add a character to the end of each filename specifying the file type

  Practice using ls to get extra information about the files you created while practicing cat, and to get a list of all files beneath your home directory:
  

  
  ls -l out1 out2
  ls -R -a ~
  
  

• The rm command is used to remove (delete) files. Make sure you are in your home directory, then delete the files out1 and out2, and check that the files no longer exist:
  

  
  cd
  ls -l
  rm out1 out2
  ls -l
  
  

  Think carefully about what you are doing when using rm. File deletion in UNIX is irreversible.
• The mkdir and rmdir commands are used to make and remove directories. Use these commands to create and then remove a directory called dir1 in your home directory with two subdirectories sub1 and sub2:
  

  
  cd
  mkdir dir1
  cd dir1
  mkdir sub1
  cd
  mkdir dir1/sub2
  ls dir1
  rmdir dir1/sub1
  cd dir1
  rmdir sub2
  cd ..
  rmdir dir1
  ls dir1
  
  

  Note that the last command should give you an errors message, since the directory dir1 no longer exists.
• The touch command is used to create empty files and to set the timestamp for files that already exist. Use touch to create three empty files called e1, e2, and e3:

  
  touch e1
  touch e2 e3
  
  

• The mv command is used to rename files or move them into new directories. The cp command is used to make copies of existing files. Use these commands to make three copies of the file /etc/hosts called c1, c2, and c3 in your home directory:

  
  cd
  cp /etc/hosts ~
  ls
  mv hosts c1
  ls
  cp c1 c2
  ls
  cp c2 c3
  ls
  
  

  Now move these newly created files into a new subdirectory called host_copies:

  
  mkdir host_copies
  mv c1 c2 c3 host_copies
  ls host_copies
  
  

  The cp command has an optional flag -r that tells it to recursively copy all subdirectories beneath a named directory. The optional -R flag to the ls command enables recursive display of all subdirectories. The rm command has two optional flags -r and -f that tell it to recursively/forcibly delete all subdirectories. These commands can be used to quickly copy, display, and destroy entire directory hierarchies:

  
  cp -r /etc/skel skel_copy
  ls -a -R skel_copy
  rm -r -f skel_copy
  ls -a -R skel_copy
  
  

  Note that multiple flags may usually be combined into a single argument for convenience:

  
  cp -r /etc/skel skel_copy
  ls -aR skel_copy
  rm -rf skel_copy
  ls -aR skel_copy
  
  

  You should be very careful about using any recursive options to commands. For example,

  NEVER TYPE THE FOLLOWING COMMAND, IT WILL WIPE OUT ALL YOUR FILES!!!

  
  rm -rf ~
  
  

• The grep command prints every line in a file matching a specified pattern. For example the following command prints every line containing the phrase local from the file /etc/hosts:

  
  grep local /etc/hosts
  
  

• The chmod command controls how other people can access your files. The first argument to chmod tells how to change the file permissions, and consists of
  1. any of the letters u (for user/owner), g (for group) o (for all others), or a (for all users), followed by
  2. one of the letters + (to add a permission), - (to take a permission away), or = (to set permissions), followed by
  3. any of the letters r (for read permission), w (for write permission), or x (for execute permission)
  The chmod command takes several optional flags, one of which (-R) enables recursion. Any additional arguments are assumed to be the names of files for which permissions should be altered. Note that ls -l lists files with the user/group/other permissions in the first few columns of each output line. Practice using the following sequence of commands, which creates a file, makes it inaccessible to everyone, then adds full permissions for the owner, execute permissions for everyone, and read permission for group members:

  
  touch newfile
  ls -l newfile
  chmod ugo-rwx newfile
  ls -l newfile
  chmod u=rwx newfile
  ls -l newfile
  chmod a+x newfile
  ls -l newfile
  chmod g+r newfile
  ls -l newfile
  
  

• The tar and gzip/gunzip commands provide functionality similar to zipfiles under MS-windows. These commands have extensive options and flags as documented in the online manual, but the following flags will provide most of the functionality you need:

  Flag	Purpose
  -z	Automatically compress/uncompress tarfile
  -x	Extract tarfile
  -c	Create tarfile
  -f	Store/Extract tarfile to/from specified file instead of standard I/O
  -v	Provide verbose information on what tar is doing

  The following three uses will be the most common for this class:
  1. Create a compressed tarfile called skel.tar.gz containing all the files in the directory /etc/skel (the tarfile is automatically filtered through gzip):

     
     tar -zcvf skel.tar.gz /etc/skel
     
     

  2. Display the contents of the compressed tarfile skel.tar.gz (the compressed tarfile is automatically filtered through gunzip):

     
     tar -ztf skel.tar.gz
     
     

  3. Extract the contents of the compressed tarfile skel.tar.gz (the compressed tarfile is filtered as above):

     
     tar -zxvf skel.tar.gz
     
     

  Note that it is also possible to perform compression/decompression manually using gzip/gunzip, in which case you will need to leave off the -z option from the tar commands:

  
  tar -cvf skel.tar /etc/skel
  gzip skel.tar
  ls -l skel.tar.gz
  gunzip skel.tar.gz
  ls -l skel.tar
  tar -tf skel.tar
  tar -xvf skel.tar
  
  

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UNIX Command Summary

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Assignment

1. My home directory contains a subdirectory m171/spring_2005/lab1. Copy this directory and all its contents into your own home directory.
2. The lab1 directory contains three subdirectories called d1, d2, and d5. You will also see a file called README. Follow the instructions in this file for steps 3-4.
5. The d2 subdirectory contains a file called instructions2. Follow the instructions in this file for step 6.
7. Create a new subdirectory called d3 containing a new empty file called empty.
8. The UNIX online dictionary is contained in the file /usr/share/dict/words. This file contains one word per line. Use these two facts to create a list of all words containing the letters 'gry'. Store this list in the file d4/grylist.
9. Store a list of all files in the directory /etc in d4/etclist.
10. Create three identical files called info1, info2, and info3 in the directory d3/subdir. Each of these should contain your username and the name of the operating system you're using, in that order.
11. Make sure the only subdirectories of your lab1 directory are d1,d2,d3, and d4.
12. Make sure no one but you can read or execute any of the files contained below your lab1 directory, and document this by generating a list of the names and permissions of all these files. Store this list in d4/permlist.
13. Save your lab1 directory as a compressed tarfile called lab1.<username>.tar.gz, where <username> is replaced by your UNIX user name. Send me an email with this tarfile as an attachment. You may use either pine or webmail to send this email.

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