IT 244: Introduction to Linux/Unix
Class 25 Exercise, Monday, December 9th

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 ex25 directory
  

      mkdir  ex25

• Go to your ex25 directory
  

      cd  ex25

while Loops

• Using your favorite editor, create the script count_to_five.sh
  

      #! /bin/bash
      #
      # prints the numbers from 1 to 5
      
      number=1
      while [ $number -lt 6 ]
      do
        echo $number
        (( number += 1 ))
      done

• Make this script executable
  

      chmod 755 count_to_five.sh

• Run this script
  

      ./count_to_five.sh

Practice using the debugging feature

• Run count_to_five.sh using the debugging feature
  

      bash -x count_to_five.sh

  Notice that each line of code is printed as it is executed, with the current value of the variable substituted for the variable name.

until Loop

• Using your favorite editor, create the script count_until.sh
  

      #! /bin/bash
      #
      # counts from 1 to its argument, then stops 
      
      number=1
      until [ $number -gt $1 ]
      do
        echo  "$number"
        (( number += 1))
      done

  Notice that this script uses the -gt, greater than, option, as opposed to the -lt, less than, option employed in the while loop script above.
  
  
• Make this script executable
  

      chmod 755 count_until.sh

• Run this script
  

      ./count_until.sh 10

continue

• Using nano, or your favorite editor, create the script continue.sh
  

      #! /bin/bash
      #
      # demonstrates how continue works
      
      total=0    
      for number in 1 2 3 4 5 6 7 8 9 10
      do
          if [ $number -eq 2 -o $number -eq 4 -o $number -eq 6 -o $number -eq 8 ]
          then  
              continue
          fi    
          echo Adding $number to $total
          (( total += $number ))
      done
      echo 
      echo total: $total

• Make this script executable
  

      chmod 755 continue.sh

• Run the script continue.sh
  

      ./continue.sh

  Notice that the echo command is not run for the values of 2, 4, 6 and 8.
  
  Instead, the loop progresses to the next value of the loop variable.

break

• Using nano, or your favorite editor, create the script break.sh
  

      #! /bin/bash
      #
      # demonstrates how break works
  
      for f in *
      do
          if  [ -x $filename ]
          then
              echo First executable file: $f
              break
          fi
      done

• Make this script executable
  

      chmod 755 break.sh

• Run the script break.sh
  

      ./break.sh

  The program examines all the files in your current directory.
  
  If it finds an executable file, it prints the name of that file and quits.

case

• Using nano, or your favorite editor, create the script case.sh
  

      #! /bin/bash
      #
      # demonstrates how the case structure works
      
      echo -n "Enter A, B, or C: "
      read letter
      case $letter in
        A|a)
          echo You entered A or a
          ;;
        B|b)
              echo You entered B or b
          ;;
        C|c)
              echo You entered C or c
          ;;
        *)
          echo You did not enter A, B, or C
          ;;
      esac
      echo Exiting program

• Make this script executable
  

      chmod 755 case.sh

• Run the program several times
  

      ./case.sh

select

• Using nano, or an editor of your choice, create select.sh
  

      #! /bin/bash
      #
      # demonstrates how the select structure works
      
      PS3="Choose your fruit: "
      select fruit in apple banana blueberry orange STOP
      do
          if [ $fruit = ""  ]
          then
              echo Invalid entry
              continue
          elif [ $fruit = STOP ]
          then
              echo About to leave
              break
          fi
          echo You chose $fruit
          echo That is choice number $REPLY
      done
      echo Exiting program

• Make this script executable
  

      chmod 755 select.sh

• Run this program choosing several different fruits
  

      ./select.sh