• What Is a Shell Script?
• Why Are There Rules for Homework Scripts?
• Rules for Homework Shell Scripts
• Example
• Mistakes That Will Cost You Points
• Mistake #1 - Never Use Certain Commands in Your Shell Scripts
• Mistake #2 - Step Must Be Capitalized
• Mistake #3 - Put Spaces in Comments
• Mistake #4 - Don't Get Step Numbers Wrong
• Mistake #5 - Unix Prompts Should Never Appear in Scripts
• Mistake #6 - Blank Line After a Step Comment
• Mistake #7 - No Blank Line Before Step Comment
• Mistake #8 - Blank Lines Between Unix Commands for a Step
• Testing a Script for Step Comments
• Additional Advantages of Running step_comment_check.sh

What Is a Shell Script?

• A shell script is a text file that contains a list of Unix commands
• With one command on each line
• You can then run a shell script from the command line and it will execute each command in turn
• Shell scripts are used to automate routine Unix administrative tasks

Why Are There Rules for Homework Scripts?

• Each shell script you submit for a homework assignment must follow certain rules
• If you violate the rules you will lose points
• Why?
• Each semester I have about 130 students in three classes
• Each class has four weekly assignments that need to be scored
• The only way I can handle this load is to automate as much of my work as possible
• For this automation to work I have to insist on certain rules
• Every time a student breaks one of these rules I have to do more work
• I deduct points to encourage students to follow the rules

Rules for Homework Shell Scripts

• You need to create a directory for each homework assignment
• This directory must be inside your hw directory
• And the hw directory must be inside your it244 directory
• The homework directory name will begin with "hw" followed by the number of the assignment
• The filename for each homework shell script must
  • Begin with "hw"
  • Followed by the homework number
  • Followed by ".sh"
• So the script for homework 3 should be named hw3.sh
• And the script should be inside an hw3 directory
• Each step in the homework MUST labeled with a Step number comment
• The comment must have the word "Step" followed by step number
• So, the line before the Unix commands that perform Step 1 should read

  # Step 1

• And the line before the Unix commands that performs Step 2 should read

  # Step 2 

• It should be "Step" not "step"
• There should also be a blank line before each Step comment but not after it
• The blank line helps me see where the commands for each step ends
• There must be no blank lines between the Unix commands for each step

Example

• Let's look at an example
• If you would like to see a video demonstrating the proper format for this example click here
• Let's say that homework 99 asks you to do the following:
  1. Go to your home directory
     Run a command that shows that you are in your home directory
  2. List the contents of your directory
  3. List the contents of /home/ghoffman/course_files/it244_files
• For this assignment you would have to create an hw99 directory inside your hw directory
• Inside this hw99 directory you would create the file hw99.sh
• Here is the text of the file

  # Step 1
  cd
  pwd
  
  # Step 2
  ls
  
  # Step 3
  ls /home/ghoffman/course_files/it244_files

Mistakes That Will Cost You Points

• There are a number of common mistakes that student make with their homework scripts
• These mistakes make it hard for me to score the assignments
• If you make any of the mistakes listed below you will lose points

Mistake #1 - Never Use Certain Commands in Your Shell Scripts

• Never use one of the following commands inside your homework script
  • more or less
  • Editors like nano, vi, vim or emacs
  • man or info
• You will never need to use these commands in a homework script

Mistake #2 - Step Must Be Capitalized

• Capitalize the word "Step"
• Don't write this

  # step 4

• Write this instead

  # Step 4

Mistake #3 - Put Spaces in Comments

• There must be a space between # and "Step"
• And a space between "Step" and the step number
• Don't write this

  #Step1

• Write this instead

  # Step 1

Mistake #4 - Don't Get Step Numbers Wrong

• I have a script that shows me all the code for a particular step, for each student
• I run this script to score your homework scripts
• If you get the step number wrong it cost me time
• And you will lose points
• Some steps need more than one command
• If you write a Step comment for each command, the numbering will be wrong
• So if Step 4 asked you to
  • Go to your home directory
  • List the contents of your home directory
• This would be wrong

  # Step 4
  cd
  
  # Step 5
  ls

• Instead, you should write

  # Step 4
  cd
  ls

Mistake #5 - Unix Prompts Should Never Appear in Scripts

• I encourage students to try a command first in a separate ssh session
• Then paste a working command into nano running in another ssh window
• But if you do this, do not copy the Unix prompt
• The script should contain Unix commands only
• The following is wrong

  it244gh@vm75:~$ # Step 1
  it244gh@vm75:~$ cd ~
  it244gh@vm75:~$ pwd
  /home/it244gh

• It should look like this

  # Step 1
  cd ~
  pwd

Mistake #6 - Blank Line After a Step Comment

• There a number of small errors that make it hard for me to read the command for each step
• One of these is to put a blank line after each Step comment
• The following is wrong

  # Step 1
  
  cd ~
  pwd

• It should look like this

  # Step 1
  cd ~
  pwd

Mistake #7 - No Blank Line Before Step Comment

• After you have written all the Unix commands for one Step
• You have to have a blank line before the next Step comment
• This means every Step comment, except the first, has a blank line before it
• The following is wrong

  # Step 1
  cd ~
  pwd
  # Step 2

• It should look like this

  # Step 1
  cd ~
  pwd
  
  # Step 2

Mistake #8 - Blank Lines Between Unix Commands for a Step

• A Step may have more than one command
• There should be no blank lines between the commands for a step
• The following is wrong

  # Step 1
  cd ~
  
  pwd

• It should look like this

  # Step 1
  cd ~
  pwd

Testing a Script for Step Comments

• Properly formatted Step comments are important
• So I have created a shell script which will check your homework file
• This script looks for each of the required Step comments
• It prints an error message if it cannot find them
• To run this script, go to the directory ~ghoffman/it244_test
• The name of the script is step_comment_check.sh
• The script requires two arguments

  $ ~ghoffman/it244_test/step_comment_check.sh
  Usage: step_comment_check.sh USERNAME HW_NUMBER

• your Unix username and the homework number

  $ ./step_comment_check.sh ghoffman 4
  # Step 1
  # Step 2
  # Step 3
  # Step 4
  # Step 5
  # Step 6
  # Step 7
  # Step 8
  # Step 9
  # Step 10

• If your script is missing a comment you will get an error message

  $ ./step_comment_check.sh ghoffman 3
  # Step 1
  # Step 2
  Could not find # Step 3
  Could not find # Step 4
  Could not find # Step 5
  ...

Additional Advantages of Running step_comment_check.sh

• The purpose of step_comment_check.sh is to check for Step comments
• But it also detects two other problems that cause a student to lose points
  • Homework scripts in the wrong directory
  • Empty or incomplete homework scripts
• When it is time to score homework assignments I run a collection script
• This script copies files from each student's directory for that assignment
• It often happens that a students create the homework script in the wrong directory
• This means my script cannot collect it and the student receives a 0 for the assignment
• step_comment_check.sh knows which directory is supposed to contain the script
• It will print an error if it cannot find the file
• Students sometimes leave empty or incomplete scripts in their homework directory
• The step checking script will also catch these errors
• Because it will not be able to find the required Step comments