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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=

===Main Objectives of this Practice Tutorial===

:* ~~Learn about additional logic control-flow statements if-else and~~ Use the '''if-elif-else''' control flow statement in a shell script.

:* ~~Learn additional uses of~~ Use the '''for ''' loop control~~-flow statement~~using a list with '''command substitution'''.

:* ~~Learn~~ Use the ~~purpose of command substitution and how it can be used with control-flow statements~~'''while''' loop in a shell script.

:* ~~List~~ Use the '''exit''' and ~~explain the purpose of several~~ '''break''' statements in a shell script. :* Explain how to configure and use a '''.bashrc''' start-up ~~files~~file.~~ ~~

===Tutorial Reference Material===

|- 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;" |~~Additional~~ '''Control Flow Statements* [https:~~//www.tutorialspoint.com/unix/if-else-statement.htm if-else]~~'''

* [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>

|}

= KEY CONCEPTS =

~~===Additional Logic Statements===~~

~~ ~~

~~[[Image:if-else.png|thumb|right|300px|Example of how an '''if-else''' statement works.]]'''if-else Statements'''~~

====IF-ELIF-ELSE STATEMENT==== [[Image:if-elif-else.png|thumb|right|300px|Example of how an '''if-elif-else''' statement works. (Image licensed under [https://creativecommons.org/licenses/by-sa/3.0/ cc])]] The '''elif''' statement can be used to perform additional conditional tests of the previous test condition tests '''FALSE'''. This statement is used to make your logic control-flow statement to be more adaptable. ''How it Works:'' If the test condition returns a '''TRUE ''' value, then the Linux Commands between '''then ''' and '''else ''' statements are executed. If the test returns a '''FALSE ''' value, then '''a new condition is tested again''', and action is taken if the result is '''TRUE''', then the Linux Commands between ~~the~~ '''then''' and '''else ~~and fi~~ ''' statements are executed.'''Additional elif statements''' can be used if additional conditional testing is required . Eventually, an action will be taken when the final test condition is '''FALSE'''.

''Example:''

num1=5 num2=10 if test $num1 –lt $num2 then    echo “Less Than” ~~else~~elif test $num1 –gt $num2 then    echo “Greater Than” else    ~~“Greater Than or Equal~~ echo “Equal to” fi

~~[[Image:if-elif-else.png|thumb|right|300px|Example of how an '''if-elif-else''' statement works.]]'''if-elif-else Statements'''~~====FOR LOOP USING COMMAND SUBSTITUTION====

If Let’s issue the ~~test condition returns~~ '''for''' loop with a ~~TRUE value, then the Linux Commands between~~'''list''' using '''command substitution'''. ~~then~~ In the example below, we will use command substitution to issue the ls command and ~~else statements are executed. ~~ If have that output (filenames) become arguments for the ~~test returns a FALSE value, then a new condition is tested,~~for loop. ~~and action is taken if the result is TRUE . Eventually, an action will be taken~~ ~~when the final test condition is FALSE~~

''Example:''

~~num1=5 num2=10~~for x in $(ls) ~~if test $num1 –lt $num2~~do ~~then~~    echo ~~“Less Than” elif test $num1 –gt~~ “The item is: $~~num2 then    echo “Greater Than” else    echo “Equal to”~~x” fidone

===~~Additional Loop Statements~~=WHILE LOOP====[[Image:while-loop.png|thumb|right|170px|Example of how a '''while''' loop works. (Image licensed under [https://creativecommons.org/licenses/by-sa/3.0/ cc])]]

~~[[Image:for-~~''The '''while''' loop is useful to loop based on the result from a test condition or command~~-substitution~~result.~~png|thumb|right|300px|Example~~ This type of ~~how a~~ loop is very useful for '''~~for loop with command substitution~~error-checking''' ~~works~~.]] How it Works: The condition/expression is evaluated, and if the condition/expression is '''~~Command Substitution~~TRUE'''~~command substitution is a facility that allows a command~~, ~~to be run and its output to be pasted back on~~ the ~~command line as arguments to another command~~code within … the block is executed.''This repeats until the condition/expression becomes '''FALSE'''. Reference: https://en.wikipedia.org/wiki/~~Command_substitution~~While_loop

~~Examples~~''Example 1:''

~~command1~~ answer=10 read –p “pick a number between 1 and 10: “ guess while test $~~(command2)~~guess –eq 10 do    read –p “Try again: “ guess ~~command1 [arguments from command2 output]~~done echo “You are correct”

''~~'for Loop using Command Substitution'~~Example 2:''

~~Let’s issue the for loop with a list using command substitution.~~value=1 while [ $value -le 5 ] ~~In the example below, we will use command substitution to issue the ls command and~~do   echo "$value" ~~have that output~~   (~~filenames~~(value=value+1) ~~become arguments for the for loop.~~) # could also use ((value++)) done 1 2 3 4 5

~~Example~~====EXIT & BREAK STATEMENTS==== '''exit Statement'''

~~for x in $(ls) do~~The '''exit''' statement is used to '''terminate''' a shell script. ~~   echo “The item~~ This statement is~~: $x” done ~~very useful when combined with logic in a shell script. The exit command can contain an argument to provide the exit status of your shell script.

''Example:'~~while Loop Statement~~'~~''�~~

~~The condition/expression is evaluated, and~~ if ~~the condition/expression is true,~~[ $# -ne 1 ] then echo "USAGE: $0 [arg]" exit 1 fi ~~the code within … the block is executed. �~~~~This repeats until the condition/expression becomes FALSE.~~ ~~Reference~~'''break</~~/en.wikipedia.org/wiki/While_loop�~~span> Statement'''

~~Example:��~~The '''break''' statement is used to '''terminate a loop'''. Although the loop terminates, the shell script will continue running.

''Example:'' answer=10<br~~>read ~~–p “pick~~ -p "Enter a number ~~between 1 and 10~~: ~~“ guess~~" number while ~~test~~ [ $~~guess –eq 10~~number -ne 5 ] do ~~   ~~ read ~~–p “Try~~ -p "Try again. Enter a number: ~~“ guess~~" number if [ $number -eq 5 ] then break fi done ~~echo “You are correct”

===~~Using Startup Files~~=START-UP FILES====

x'''Shell configuration (start-up) files''' are '''scripts''' that are run when you log in, log out, or start a new shell. The start-up files can be used, for example, to '''set the prompt and screen display''', '''create local variables''', or create temporary Linux commands ('''aliases''')

~~=INVESTIGATION 1: ADDITIONAL LOGIC STATEMENTS=~~The '''/etc/profile''' file belongs to the root user and is the first start-up file that executes when you log in, regardless of shell.

User-specific config start-up files are in the user's home directory:

<ul><li>'''~/.bash_profile''' runs when you log in. </li><li>The '''~/.bashrc''' runs when you start an interactive Bash shell.</li></ul>

~~In this section, you will learn how to .~~'''Logout Files''' There is a file that '''resets or restores the shell environment''' (including shut-down of programs running in the shell) when the user logs out of their shell.User-specific logout start-up files are in the user's home directory: '''~/.bash_logout''' =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 '''more adaptable'''.

'''Perform the Following Steps:'''

# '''Login''' to your matrix account. # Issue a command to '''confirm''' you are located in your home directory. # Issue a Linux command to create a directory called '''advanced''' # Issue a Linux command to change to the '''advanced''' directory. # Issue a Linux command to confirm you are located in the '''advanced''' directory. In '''tutorial 10''', you learned how to use the '''if''' control-flow statement. You will now learn to use the '''if-else''' statement to take two different actions based on if the condition tests either TRUE or FALSE. # Use a text editor like vi or nano to create the text file called '''if-4.bash''' (eg. vi if-4.bash) # Enter the following lines in your shell script: #!/bin/bash clear read -p "Enter the first number: " num1 read -p "Enter the second number: " num2 if [ $num1 -gt $num2 ] then    echo "The first number is greater than the second number." elif [ $num1 -lt $num2 ] then    echo "The first number is less than the second number." else    echo "The first number is equal to the second number." 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-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 received an A grade." elif [ $mark -ge 70 ] then    echo "You received a B grade." elif [ $mark -ge 60 ] then    echo "You received a C grade." elif [ $mark -ge 50 ] then    echo "You received a D grade." else    echo "You 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''' 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?

# Issue the following linux command: echo $* What do you notice? These positional parameters can be used with a for loop. To simplify things, let's create another shell script that uses '''command substitution''' within a '''for''' loop.

# Use a text editor like vi or nano to create the text file called '''for-3.bash''' (eg. vi for-3.bash)

# Enter the following lines in your shell script: #!/bin/bash clear set 10 9 8 7 6 5 4 3 2 1 for x do    echo $x done echo "blast-off!"