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Tutorial12: Shell Scripting - Part 2

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{{Admon/caution|DO NOT USE THIS VERSION OF THE LAB. This page will no longer be updated.|'''New version here:''' https://seneca-ictoer.github.io/ULI101/A-Tutorials/tutorial12 '''Andrew's students please go here:''' http://wiki.littlesvr.ca/wiki/OPS145_Lab_11}}

=ADDITIONAL SHELL SCRIPTING=

|- valign="top" style="padding-left:15px;"

|colspan="2" |~~Course Notes~~'''Slides:'''<ul><li>Week 12 Lecture 1 Notes: [https://~~ict~~wiki.cdot.senecacollege.ca/~~~murray.saul~~uli101/~~uli101~~slides/ULI101-~~Week12~~12.1.pdf PDF] | [https://~~ict~~wiki.cdot.senecacollege.ca/~~~murray.saul~~uli101/~~uli101~~slides/ULI101-~~Week12~~12.1.pptx PPTX]</li></ul>

| style="padding-left:15px;" |'''Control Flow Statements:'''

* [https://www.tutorialspoint.com/unix/if-else-statement.htm if-elif-else]

* [https://www.cyberciti.biz/faq/bash-for-loop/#:~:text=A%20'for%20loop'%20is%20a,files%20using%20a%20for%20loop. for Loop]

* [https://bash.cyberciti.biz/guide/While_loop while Loop]

'''Additional Statements:'''

* [https://www.geeksforgeeks.org/exit-command-in-linux-with-examples/#:~:text=exit%20command%20in%20linux%20is,last%20command%20that%20is%20executed.&text=After%20pressing%20enter%2C%20the%20terminal%20will%20simply%20close. exit]

* [https://www.geeksforgeeks.org/break-command-in-linux-with-examples/#:~:text=break%20command%20is%20used%20to,The%20default%20number%20is%201. break]

| style="padding-left:15px;"|'''Startup Files:'''

* [https://www.gnu.org/software/bash/manual/html_node/Bash-Startup-Files.html Purpose]

* [http://www.linuxfromscratch.org/blfs/view/svn/postlfs/profile.html Examples]

|colspan="1" style="padding-left:15px;" width="30%"|'''Brauer Instructional Videos:'''<ul><li>[https://www.youtube.com/watch?v=XVTwbINXnk4&list=PLU1b1f-2Oe90TuYfifnWulINjMv_Wr16N&index=6 Bash Shell Scripting - Part 2]</li></ul>

|}

=INVESTIGATION 1: ADDITIONAL LOGIC STATEMENTS=

'''ATTENTION''': ~~Effective '''May 9, 2022''' - this~~ This online tutorial will be required to be completed by '''Friday in week 13 by midnight'''~~ ~~to obtain a grade of '''2%''' towards this course

In this investigation, you will learn additional control-flow statements to allow your shell scripts to be even '''more adaptable'''.

# Issue a Linux command to confirm you are located in your '''advanced''' directory in your Matrix account.

# Issue the following Linux command to view the ~./for-1.bash file: more ~./for-1.bash) As you should have noticed from '''tutorial 10''' that the '''for''' loop can use a '''list'''. You can also use the for loop with positional parameters stored as '''arguments''' from an executed shell script. You can also use the '''for''' loop with a list using '''command substitution'''. Using command sustitution is an effective method to loop within a shell script. Before creating a new shell script, let's learn to use command substitution from the Bash Shell to store arguments as positional parameters and use them for practice.

# Issue the following linux command to set positional parameters in your current shell: set apples oranges bananas pears

# Issue the following linux command: echo $# What do you notice? What does this value represent?

# Save your editing session and exit the text editor (eg. with vi: press '''ESC''', then type ''':x''' followed by '''ENTER''').

# '''Add execute permissions''' for this shell script and '''run Bash shell script''' What do you notice? Does the output for this shell script differ from '''for-4.bash'''? Why? We now want to introduce you to the use of '''error-checking'''.

# Use the '''more''' command to view the previously-created Bash shell script '''~./if-5.bash''' (eg. more ~./if-5.bash) Take a few moments to re-familiarize yourself with this shell script # Run your shell script by issuing: ~./if-5.bash When prompted, enter a '''letter''' instead of a ''number''. What happens? Let's edit the '''for-5.bash''' shell script to perform '''error-checking''' to force the user to enter a numeric value between '''0''' and '''100'''. '''NOTE:''' The '''while''' statement can be used with the '''test''' command (or a simple linux command or a linux pipeline command) for error checking. In our case, we will use a pipeline command with extended regular expressions. In order to loop while the result is TRUE (not FALSE), you can use the negation symbol (!) to set the test condition to the opposite. # Use a text editor like vi or nano to edit the text file called '''~./if-5.bash''' (eg. vi ~./if-5.bash)

# Add the following lines in your shell script IMMEDIATELY AFTER the read statement to prompt the user for a mark: while ! echo $mark | egrep "^[0-9]{1,}$" > /dev/null 2> /dev/null do    read -p "Not a valid number. Enter a mark (0-100): " mark done

# Save your editing session and exit the text editor (eg. with vi: press '''ESC''', then type ''':x''' followed by '''ENTER''').

# Run your shell script by issuing: ./if-5.bash

# When prompted, enter a '''letter''' instead of a ''number''. What happens? Does the shell script allow you to enter an invalid grade like '''200''' or '''-6'''? Let's add an '''additional error-checking loop''' to force the user to enter a number between '''0''' and '''100'''. Compound operators like '''&&''' and '''||''' can be used with the '''test''' command. Let's use the '''||''' compound criteria to to NOT accept numbers '''outside''' of the range '''0''' to '''100'''.

# Use a text editor like vi or nano to edit the text file called '''~./if-5.bash''' (eg. vi ~./if-5.bash)

# Add the following lines in your shell script IMMEDIATELY AFTER the PREVIOUSLY ADDED error-checking '''while''' loop statement to '''force''' the user to enter a valid number (between 1 and 100): while [ $mark -lt 0 ] || [ $mark -gt 100 ] do    read -p "Invalid number range. Enter a mark (0-100): " mark done

# Save your editing session and exit the text editor (eg. with vi: press '''ESC''', then type ''':x''' followed by '''ENTER''').

# Run your shell script by issuing: ~./if-5.bash

# When prompted, enter a '''letter''' instead of a ''number''. What happens? Does the shell script allow you to enter an '''invalid grade''' like '''200''' or '''-6'''? Let's reinforce '''math operations''' in a shell script (that you created in '''tutorial 10''') and then incorporate math operations within a loop.

# Use a text editor like vi or nano to create the text file called '''for-6.bash''' (eg. vi for-6.bash)

# '''Exit''' your current Bash shell session.

# '''Login''' again to your matrix account. What did you notice this time?

# After you complete the Review Questions sections to get additional practice, then work on your '''online assignment 3,''' '''sections 4 to 6''' labelled: '''More Scripting (add)''', '''Yet More Scripting (oldfiles)''', and '''sed And awk'''

= FURTHER STUDY =

simulate a quiz:

https://~~ict~~wiki.cdot.senecacollege.ca/~~~murray.saul~~uli101/~~uli101~~files/uli101_week12_practice.docx

Your instructor may take-up these questions during class. It is up to the student to attend classes in order to obtain the answers to the following questions. Your instructor will NOT provide these answers in any other form (eg. e-mail, etc).

# Write code for the '''~/.bash_profile''' file below to clear the screen, welcome the user by their username, and display a list of all users currently logged into your Matrix server. Insert blank lines between each of those elements.

# Write a command to run the recently created '''~/.bash_profile''' startup file from the previous question without exiting and re-logging into your Matrix account.

_________________________________________________________________________________

Author: Murray Saul

License: LGPL version 3

Link: https://www.gnu.org/licenses/lgpl.html

_________________________________________________________________________________

[[Category:ULI101]]

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