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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''': 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 '''~~even~~ more adaptable'''.

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

# Issue the following linux command to add execute permissions for your shell script: chmod u+x if-4.bash

# Run your shell script by issuing: ./if-4.bash Try running the script several times with numbers different and equal to each other to confirm that the shell script works correctly. A classic shell script to demonstrate many different paths or actions to take depending of multiple testing using an '''if-elif-else''' statement would be a '''mark to letter grade converter'''.

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

# Enter the following lines in your shell script: #!/bin/bash clear read -p "Enter a mark (0-100): " mark if [ $mark -ge 80 ] then    echo "You ~~receive~~ received an A grade." elif [ $mark -ge 70 ] then    echo "~~The receive~~ You received a B grade." elif [ $mark -ge 60 ] then    echo "~~The receive~~ You received a C grade." elif [ $mark -ge 50 ] then    echo "~~The receive~~ You received a D grade." else    echo "You ~~receive~~ received an F grade." fi

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

# Issue the following linux command to add execute permissions for your shell script: chmod u+x if-5.bash

# Run your shell script by issuing: ./if-5.bash What do you notice? Run several times to confirm that the shell script runs correctly for all mark (grade) categories.

# Issue the following to run a checking script: ~uli101/week12-check-1

# If you encounter errors, make corrections and '''re-run''' the checking script until you receive a congratulations message, then you can proceed.

:In the next investigation, you will learn more about the '''for''' loop and learn how to use the '''while''' loop for '''error-checking'''.

=INVESTIGATION 2: ADDITIONAL LOOPING STATEMENTS =

In this investigation, you will learn more about the '''for''' loop and learn how to use the '''while''' loop for '''error-checking'''.

'''Perform the Following Steps:'''

# Issue a Linux command to confirm you are located in your '''advanced''' directoryin 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?

# '''Add execute permissions''' for the owner of this script and '''run this Bash shell script'''. What do you notice? Let's create another shell script to '''run a loop for each file''' that is contained in your current directory using '''command substitution'''.

# Use a text editor like vi or nano to create the text file called '''for-4.bash''' (eg. vi for-4.bash)

# Enter the following lines in your shell script: #!/bin/bash clear set $(ls) echo "Here are files in my current directory:" echo for x do    echo "    $x" done

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

# '''Add execute permissions''' and '''run''' this Bash shell script. What do you notice? We can reduce a line in our shell script by using '''command substitution''' in the for loop instead of using the '''set''' command. Let's demonstrate this in another shell script.

# 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: ./~~for~~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 ~~code block~~ '''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)

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

# Set execute permissions for this shell script and run your shell script by issuing: ./for-6.bash '''You should have noticed an error message'''.

# To demonstrate what went wrong, issue the following '''commands''': num1=5;num2=10 result=$num1+$num2 echo $result Notice that the user-defined variable stores the text "'''10+5'''" which is NOT the expected result of adding the number '''10 ''' and '''5'''. As you may recall in '''tutorial 10''', we need to convert a number stored as text into a '''binary number''' for calculations (in this case, advance the value by 1 for each loop). We can accomplish this by using the math construct '''(( ))'''

# To demonstrate, issue the following set of '''commands''': num1=5;num2=10 sum=$(($num1+$num2)) echo $sum ((product=$num1*$num2)) echo $product Let's correct our '''for-6.bash''' shell script to correctly use math operations.

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

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

# '''Run''' this Bash shell script again. What do you notice this time?

# Issue the following to run a checking script: ~~bash /home/murray.saul/myscripts~~~uli101/week12-check-12

# If you encounter errors, make corrections and '''re-run''' the checking script until you receive a congratulations message, then you can proceed.

:In the next investigation, you will learn to use the '''exit''' statement to '''terminate the execution of a shell script''' if not run with the properly number of arguments and use the '''break''' statement that will '''terminate a loop''' but NOT terminate the running of the shell script. =INVESTIGATION 3: exit AND break STATEMENTS= In this investigation, you will learn to use the '''exit''' and '''break''' statements in your shell scripts. '''THE EXIT STATEMENT''' The '''exit''' statement is used to terminate a shell script. This statement is very useful when combined with logic in a shell script to display an '''error message''' if the command was '''improperly executed''' and '''terminate''' the running of the shell script. The ''exit'' command can contain return a ''value'' to provide the '''exit status''' of your shell script (i.e. TRUE or FALSE value). '''Perform the Following Steps:''' # Make certain that you are logged into matrix account. # Confirm that you are currently located in the '''advanced''' directory. # Use a text editor like vi or nano to create the text file called '''exit.bash''' (eg. vi exit.bash) # Enter the following lines in the '''exit.bash''' shell script: #!/bin/bash if [ $# -ne 1 ] then   echo "USAGE: $0 [arg]" >&2   exit 1 fi echo "The argument is: $1" # 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 Bash shell script. # Issue the following command (without arguments): ./exit.bash What did you notice? Since there are no arguments, the test~~-out~~ within the running shell script returns FALSE, then an '''error message''' with feedback of how to properly issue the shell script with an argument and then '''terminates''' the Bash shell script. Notice that the '''$0''' positional parameter displays the '''name''' of the currently running shell script in the USAGE message. This is useful in case you decide to '''change''' the ''name'' of the shell script at a later time. The symbol '''>&2''' redirects '''standard output''' from the USAGE message to '''~standard error''' making like a real error message.~~bashrc~~ This "''neat redirection trick' ~~start~~'" will NOT be considered for evaluation for this coverage. # Issue the following Linux command: echo $? What does this '''exit status''' from the previously issued command indicate? # Issue the following command (with an argument): ./exit.bash uli101 What did you notice this time? # Issue the following Linux command: echo $? What does this '''exit status''' from the previously issued command indicate? # Issue the following command (with two arguments and redirecting stderr to a file ): ./exit.bash uli101 Linux 2> error.txt What did you notice this time? # Issue the following Linux command: echo $? # Issue the following Linux command to ~~customize your Bash shell~~confirm that stderr was redirected to a file: cat error.txt

~~=INVESTIGATION 3: USING START-UP FILES =~~'''THE BREAK STATEMENT'''

The '''break''' statement is used to '''terminate''' a '''loop''' without terminating the running shell script. '''Perform the Following Steps:''' # Make certain that you are logged into matrix account. # Confirm that you are currently located in the '''advanced''' directory. # Use a text editor like vi or nano to create the text file called '''break-1.bash''' (eg. vi break-1.bash) # Enter the following lines in the '''break-1.bash''' shell script: #!/bin/bash read -p "Enter an integer: " number while ! echo $number | egrep "^[0-9]{1,}$" > /dev/null 2> /dev/null || [ $number -ne 5 ] 2> /dev/null do   if [ $number -eq 5 ] 2> /dev/null   then      break   fi   read -p "Try again. Enter a valid integer: " number done echo "The number is: $number" # 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 Bash shell script. # Issue the following command (without arguments): ./break-1.bash When prompted, enter several '''invalid''' and '''valid''' integers. Then enter '''valid integers''' NOT containing the value of '''5'''. Finally, enter the integer with the value of '''5'''. What happens? Let's use the '''break''' statement with the '''for''' loop. # Use a text editor like vi or nano to create the text file called '''break-2.bash''' (eg. vi break-2.bash) # Enter the following lines in the '''break-2.bash''' shell script: #!/bin/bash for x do   if [ $x = "uli101" ]   then      break   fi   echo "Argument is: $x" done echo echo "Shell script has been completed" # 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 Bash shell script. # Issue the following command (with arguments): ./break-2.bash hwd101 ipc144 uli101 apc100 What do you notice? How come '''uli101''' and '''apc100''' are NOT displayed but a message appeared at the end of the script that the script completed? # Issue the following to run a checking script: ~uli101/week12-check-3 # If you encounter errors, make corrections and '''re-run''' the checking script until you receive a congratulations message, then you can proceed. : In the next investigation, we will learn to create / modify '''startup files''' to customize your Linux shell environment. =INVESTIGATION 4: USING START-UP FILES = In this investigation, you will learn how to '''customize''' your '''Bash Linux shell environment''' by creating and testing a '''start-up ''' file.

# Issue a Linux command to change to your '''home''' directory.

# Issue a Linux command to confirm you are located in the '''home''' directory.

# Use the '''more''' command to view the contents of the '''default start-up ''' file called '''/etc/profile''' ~~(eg. more /etc/profile)~~ This file contains the '''default settings''' when you open your Bourne shell (eg. if issuing the command '''sh'''). # Use the '''more''' command to view the contents of the start-up file called '''/etc/bashrc''' ~~(eg. more /etc/bashrc)~~ This file contains the '''default settings''' when you '''open your Bash shell''' (eg. if issuing the command '''bash'''). Since we are using the '''Bash shell ''' by default, let's create a '''customized Bash start-up file'''. This startup file is located in your '''home''' directory using the name "'''.~~bashrc~~bash_profile'''" # Let's move your .~~bashrc~~ bash_profile file to prevent '''accidental overwrite'''. # Issue the following linux command: mv ~/.~~bashrc~~ bash_profile ~/.~~bashrc~~bash_profile.bk If you experience an error message "''No such file or directory''", just ignore this command since there is no ~~startup~~ '''~/.bash_profile''' file ~~to backup~~in your home directory. # Use a text editor like vi or nano to create the text file called '''~/.~~bashrc~~bash_profile''' (eg. vi ~/.~~bashrc~~bash_profile) If you are using the nano text editor, refer to notes on text editing in a previous week in the course schedule. # Enter the following lines in your shell script (the symbol "[" is the open square bracket symbol): clear echo -e -n "\e[0;34m" echo "Last Time Logged in (for security):" echo lastlog -u $USER echo echo -e -n "\e[m" '''NOTE:''' You will notice there is '''NO she-bang line''' since this is a '''start-up''' file.

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

# You can test run the startup file without exiting and re-entering your Bash shell environment. Issue the following: . ~/.~~bashrc~~bash_profile What do you notice? # '''Exit ''' your current Bash shell session. # '''Login''' again to your matrix account. Did you start-up file customize your Bash shell environment with colours? '''NOTE:''' This is where you can make your Linux shell environment values '''persistent''' (i.e. saved regardless of exit and login to your Bash Shell such as '''aliases''', '''umask''', etc.). # Issue the following linux command to '''restore ''' your previous settings for your bashrc startup file: mv ~/.~~bashrc~~bash_profile.bk ~/.~~bashrc~~bash_profile If you experience an error message "''No such file or directory''", just ignore. # ~~After you complete the Review Questions sections to get additional practice, then work on your~~ '''~~online assignment 3,~~Exit'''your current Bash shell session. # '''~~sections 4 to 6''' labelled: '''More Scripting (add)''', '''Yet More Scripting (oldfiles)''', and '''sed And awk~~Login'''again to your matrix account. What did you notice this time?

= FURTHER STUDY =

I hope this series of tutorials have been helpful in teaching you basic Linux OS skills.

In order to get efficient in working in the Linux environment requires '''practice''' and '''applying''' what you have learned to ~~administering~~ perform Linux operating ~~systems~~ system administration including: '''user management''', '''installing and removing applications''', '''network services''' and '''network security'''.

Although you are '''NOT''' required to perform '''Linux administration''' for this course, there are useful '''course notes''' and '''TUTORIALS''' for advanced Linux server administration that have been created for the Networking / Computer Support Specialist stream:

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).

'''Review Questions:'''

# ~~Create~~ Write code for a Bash shell script ~~called '''retire.bash'''~~ that ~~when run,~~ clears the screen, and then prompts the user for their age. If the age entered is less than 65, then display a message that the person is NOT eligible to retire. If the age is equal to 65, then display a message that the person just turned 65 and can retire. If the age is greater than 65, then display the message that the user is over 65 and why have they not have already retired already? # Add code to the ~~'''retire.bash'''~~ script created in the previous question to force the user to enter only an '''integer''' to provide error-checking for this shell script. #Write code for a Bash shell script that will prompt the user for a '''valid POSTAL CODE'''. A valid postal code consists of the following format: '''x#x #x#''' where '''x''' represents an upper or lowercase letter and '''#''' represents a number from 0-9 Also VALID postal codes can consist of no spaces or one or more spaces in the format shown above. If the user enters an '''INVALID postal code''', indicate an error and allow the user to enter the VALID postal code. When the user enters a VALID postal code, then clear the screen and display the VALID postal code. # Write code that works similar to the previous question, but have it read an input file called '''unchecked-postalcodes.txt''' and only save VALID postal codes to a file called: '''valid-postalcodes.txt''' Design your Bash Shell script to only run if the user enters TWO ARGUMENTS: '''unchecked-postalcodes.txt''' and '''valid-postalcodes.txt''' Otherwise, display an error message and immediately exit your Bash Shell script with a false exit value.

# What is the purpose of the '''/etc/profile''' startup file?

# What is the purpose of the '''/etc/bashrc''' startup file?

# What is the purpose of the '''~/.bashrc''' startup file?

# What is the purpose of the '''~/.bash_profile''' file?

# What is the purpose of the '''~/.bash_logout''' file?

# Write code for the '''~/.~~bashrc~~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 '''~/.~~bashrc~~bash_profile''' startup file from the previous question without exiting and re-logging into your Matrix account. _________________________________________________________________________________ Author: Murray Saul License: LGPL version 3Link: https://www.gnu.org/licenses/lgpl.html _________________________________________________________________________________

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