IT 244: Introduction to Linux/Unix
Class 22 Exercise, Tuesday, April 28th

Log in to users

• Log in to a Windows machine or your own laptop
  

  Enter your Unix username as the account name. Then enter your password.

• Run the ssh client
  

  Use the values in the table below to connect to users.

  ssh configuration parameter	value
  protocol	ssh
  ssh version	2
  ssh port	22
  host	users.cs.umb.edu
  user name	your Unix username
  Authentication method	password

  
  
• Enter your password

  A dialog box will appear on the screen into which you must type the password for your Unix account.

Directory for this Exercise

• Go to your ex directory

      cd  ~/it244/ex

• Create an ex22 directory
  

      mkdir  ex22

• Go to your ex22 directory
  

      cd  ex22

Start Up a script Session

Execute the script command, using the --flush option

    script --flush

History Expansion

• Look at your last 20 command lines
  

      history 20

  Notice that your definitions of functions appear on a single line, with each line of your original set of commands separated by a semi-colon.
  
  
• Rerun one of your previous commands
  
  Pick a command that will not change your current directory.

      !EVENT_ID

  Notice that it prints out the command line before executing it.
  
  
• Look at your last 10 command lines where you ran ls
  

      history | grep ls | tail

• Rerun your last command line that used echo
  

      !ec

Brace Expansion

• Create some files using braces
  

      touch test{1,2,3,4,5}.txt

• Look at the files you just created
  

      ls test?.txt

• Create some additional files using braces
  

      touch {foo,bar,bletch}.txt

• Display all the files you created
  

      ls *.txt

Tilde,  ~  , Expansion

• Display the value of tilde
  

      echo ~

• Use tilde to display the address of my home directory
  

      echo ~ckelly

• Use tilde followed by a string that is not a Unix ID
  

      echo ~xxx

  Bash cannot make any sense out of this expression, so it doesn't try.
  
  
• Use ~+ to display the address of your current directory
  

      echo ~+

• Use ~- to display the address of your previous directory
  

      echo ~-

Arithmetic Expansion

• Create two numeric variables
  

      a=3; b=6

• Display the values of these new variables
  

      echo "a = $a, b = $b"

• Use these variables in an arithmetic expression
  

      echo $(( $a + $b ))

• Use these variables in another arithmetic expression
  

      echo $(( a - b ))

  Notice that you did not need to put dollar signs ($) in front of the variable names.
  
  
• Use these variables in still another arithmetic express
  

      echo $((a*b))

  Notice that you do not need to use spaces to separate any of the elements of the expression.
  
  
• Create one last arithmetic expression
  

      echo $((b/a))

Command Substitution

• Use command substitution to see the permissions on the python executable file
  

      ls -l $(which python)

• Use command substitution to set the value of a variable
  

      now=$(date)

• Display the value of this new variable
  

      echo $now

Pathname Expansion

• Display all files ending in ".txt"
  

      ls *.txt

• Display the "test" files created earlier
  

      ls test?.txt

• Display the first two "test" files
  

      ls test[12].txt

Exit Your script Session

Use the exit command

    exit

You should see a confirmation message confirming that the script session is finished, resulting in a file called typescript. I will look at the typescript file, along with the other files in your directory.

Bash Script for this Exercise

• Make sure you are in your ex22 directory
  

      cd  ~/it244/ex/ex22

• Create the script ex22.sh
  

      nano  ex22.sh

• Write into this file the commands you used in some of the previous section
  
  Include Unix commands from the section Brace Expansion, to the section Pathname Expansion. Do not put the commands from the History expansion section in this script.
  
  
• Save this file
  
  Save and quit.
  
  
• Make this scipt executable
  

      chmod 755 ex22.sh

• Test the script
  

      ./ex22.sh

  Fix any errors you find.
  
  If you have trouble, see me.