IT 244: Introduction to Linux/Unix
Class 23 Exercise, Thursday, April 30th

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 ex23 directory
  

      mkdir  ex23

• Go to your ex23 directory
  

      cd  ex23

Start Up a script Session

Execute the script command, using the --flush option

    script --flush

test with Numbers

• Use test with the  -eq  (equality for numbers) operator
  

      test 4 -eq 5; echo $?

  Since anything other than 0 as an exit status signals failure, this means that the equality test has failed.
  
  
• Use the  -eq  operator with the same number on both sides
  

      test 4 -eq 4; echo $?

  Since 0 means success, this means that the expression evaluated to true.
  
  
• Use test with the  -ne  (not equal for numbers) operator
  

      test 4 -ne 5; echo $?

  0 means true.
  
  
• Use  -ne  again
  

      test 4 -ne 4; echo $?

  1 means false.
  
  
• Use test with the  -gt  (greater than) operator
  

      test 4 -gt 5  ; echo $?
      test 5 -gt 4  ; echo $?

• Use the  -ge  (greater than or equal to) operator
  

      test 5 -ge 4 ; echo $?
      test 5 -ge 5 ; echo $?

• Use the  -lt  (less than operator)
  

      test 4 -lt 5 ; echo $?
      test 5 -lt 4 ; echo $?

• Use the  -le  (less than or equal to) operator
  

      test 4 -le 5 ; echo $?
      test 4 -le 4 ; echo $?

test with String Comparison Operators

• Use test with the  =  (string equality) comparison operator
  

      test foo = foo ; echo $?
      test foo = bar ; echo $?

• Use test with the  !=  (string not equal) comparison operator
  

      test foo != bar  ; echo $?
      test foo != foo  ; echo $?

test with Single String Operators

• Use test with the  -n  (length greater than 0) string operator
  

      test -n foo ; echo $?
      test -n "" ; echo $?

• Use test with the  -z  (length is 0) string operator
  

      test -z "" ; echo $?
      test -z foo ; echo $?

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.

arg_test.sh

• Make sure you are in your ex23 directory
  

      cd ~/it244/ex/ex23

• Using your favorite editor create the script arg_test.sh
  

      #! /bin/bash
      #
      # responds with the number of the arguments given
      # to this script
  
      if test $# -eq 0
      then
          echo You entered no arguments
      fi
      if test $# -eq 1 
      then
          echo You entered 1 argument
      fi
      if test $# -eq 2 
      then
          echo You entered 2 arguments
      fi
      if test $# -gt 2
      then
          echo You entered more than 2 arguments
      fi

• Make sure you are in your ex23 directory
  

      cd ~/it244/ex/ex23

• Re-Start Your script Session
  Execute the script command, using both the --flush option AND the --append option
  

      script --flush --append

• Change the permissions on arg_test.sh to make it executable
  

      chmod 755 arg_test.sh

• Test the script several times
  

      ./arg_test.sh
      ./arg_test.sh foo
      ./arg_test.sh foo bar
      ./arg_test.sh foo bar bletch

• Notify me when you have finished this script
  

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.