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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.

~~[[Image:while-loop.png|thumb|right|170px|Example of how a~~ ''~~'while''' loop works.]]'''while Loop Statement'~~Example:''

~~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====

'''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''')

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 ~~sub~~Bash shell.</li></ul> '''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 shellscript: #!/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:'''

~~Logout Files~~# 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!" # Save your editing session and exit the text editor (eg. with vi: press '''ESC''', then type ''':x''' followed by '''ENTER'''). # '''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. # Use a text editor like vi or nano to create the text file called '''for-5.bash''' (eg. vi for-5.bash) # Enter the following lines in your shell script: #!/bin/bash clear echo "Here are files in my current directory:" echo for x in $(ls) 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''' 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) # Enter the following lines in your shell script: #!/bin/bash value=1 while [ $value -le 5 ] do   echo "$value"   value=value+1 done # 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) # Edit '''line 6''' and replace with the following: ((value=value+1)) '''Note:''' For those familiar with other programming languages, you can achieve the same results by using: '''((value++))''' # 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: ~uli101/week12-check-2 # 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.

~~There are files that reset or restore the environment or properly shut~~=INVESTIGATION 3: exit AND break</~~.bash_logout'''~~span> STATEMENTS=

~~=INVESTIGATION 1: ADDITIONAL LOGIC STATEMENTS=~~

In this ~~section~~investigation, you will learn ~~additional control-flow~~ to use the '''exit''' and '''break''' statements ~~to allow~~ in your shell scripts ~~to be more flexible~~.

'''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:'''

# ~~'''Login''' your~~ Make certain that you are logged into matrix account. # ~~Issue a command to '''confirm'''~~ Confirm that you are currently located in ~~your home directory. In a previous tutorial, you learned how to using~~ the '''~~if''' control-flow statement. You will now learn to use the '~~advanced''~~if-else~~'~~'' statement to take two different actions based on if the condition tests either TRUE OR FALSE~~directory. # Use a text editor like vi or nano to create the text file called '''~~if-3~~exit.bash''' (eg. vi ~~if-3~~exit.bash)~~ 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~~ the '''exit.bash''' shell script: #!/bin/bash ~~clear read -p "Enter the first number: " num1 read -p "Enter the second number: " num2~~ if [ $~~num1~~ # -~~gt $num2~~ ne 1 ] then   echo "USAGE: $0 [arg]" >&~~nbsp~~amp;2  ~~echo "The first number is greater than the second number."~~exit 1 fi ~~else~~ ~~   ~~echo "The ~~first number~~ argument is ~~less than or equal to the second number.~~: $1"~~ fi~~ # Save your editing session and exit the text editor (eg. with vi: press '''ESC''', then type ''':wxx''' followed by '''ENTER'''). # ~~Issue the following linux command to add~~ '''Add execute permissions ''' for ~~your~~ this Bash shell script~~: chmod u+x if-3~~.~~bash~~ # ~~Run your shell script by issuing~~Issue the following command (without arguments): ./~~if-3~~exit.bash What do did you notice? ~~Try~~ Since there are no arguments, the test within the running shell script returns FALSE, then an '''error message''' with feedback of how to properly issue the shell script ~~several times~~ with ~~numbers different~~ an argument and ~~equal to each other to~~then '''terminates''' the Bash shell script. ~~confirm~~ Notice that the '''$0''' positional parameter displays the '''name''' of the currently running shell script ~~works correctly.~~ ~~It would be nice to have a separate result of~~ in the ~~numbers are equal to each other~~USAGE message. ~~In order~~ This is useful in case you decide to ~~achieve this, you can use an~~ '''~~if-elif~~change''' the ''name''~~-else statement~~of the shell script at a later time. ~~# Use a text editor like vi or nano~~ The symbol '''>&2''' redirects '''standard output''' from the USAGE message to ~~create the text file called~~ '''~~if-4~~standard error''' making like a real error message.~~bash~~ This "''neat redirection trick'' ~~(eg~~" will NOT be considered for evaluation for this coverage. # Issue the following Linux command: ~~vi if-4.bash~~echo $?) ~~If you are using~~ What does this '''exit status''' from the ~~nano text editor, refer to notes on text editing in a previous week in the course schedule.~~previously issued command indicate? # ~~Enter~~ Issue the following ~~lines in your shell script~~command (with an argument): ~~#!/bin~~./exit.bashuli101<br/span>~~clear~~ ~~read -p "Enter the first number: " num1~~ ~~read -p "Enter the second number: " num2~~What did you notice this time? ~~if [ $num1 -gt $num2 ]~~ ~~then~~# Issue the following Linux command: ~~&nbsp~~echo ~~"The first number is greater than the second number."~~$?<br/span>~~elif [ $num1 -gt $num2 ]~~ ~~then~~ ~~   echo "The first number is less than~~ What does this '''exit status''' from the ~~second number."~~previously issued command indicate? ~~else~~ ~~   echo "The first number is equal~~ # Issue the following command (with two arguments and redirecting stderr to ~~the second number."~~a file): fi</spanstyle="color:blue;font-weight:bold;font-family:courier;">~~ # Save your editing session and~~ ./exit ~~the text editor (eg~~. ~~with vi: press '''ESC''', then type ''':wx''' followed by '''ENTER''')~~bash uli101 Linux 2> error.txt ~~NOTE: You should~~ What did you notice in this control-flow statement differs from an if-else statement since if the first condition is FALSE, it is tested again, which can produce two different actions depending if the second test is TRUE or FALSE.time? # Issue the following ~~linux~~ Linux command ~~to add execute permissions for your shell script~~: ~~chmod u+x if-4.bash~~echo $? # ~~Run your shell script by issuing~~Issue the following Linux command to confirm that stderr was redirected to a file: cat error.~~/if-4.bash~~txt ~~What do you notice? Try running the script several times with numbers different and equal to each other to confirm that the shell script works correctly.~~ '''THE BREAK STATEMENT'''

The '''break''' statement is used to '''terminate''' a '''loop''' without

terminating the running shell script.

'''Perform the Following Steps:'''

In # Make certain that you are logged into matrix account. # Confirm that you are currently located in the ~~next investigation~~'''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 $number | egrep "^[0-9]{1, ~~you will learn more about~~ }$" > /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'''forthis Bash shell script. # Issue the following command (without arguments): ./break-1.bash When prompted, enter several '''invalid''' ~~loop~~ and ~~learn how to~~ '''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 '''~~while~~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 ~~error~~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 checkingscript until you receive a congratulations message, then you can proceed.

~~=INVESTIGATION 2~~: ~~ADDITIONAL LOOPING STATEMENTS =~~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 ~~section~~investigation, you will learn how to ..'''customize''' your '''Bash Linux shell environment''' by creating and testing a '''start-up''' file.

'''Perform the Following Steps:'''

# 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''' 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''' 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 "'''.bash_profile'''" Let's move your .bash_profile file to prevent '''accidental overwrite'''. # Issue the following linux command: mv ~/.bash_profile ~/.bash_profile.bk If you experience an error message "''No such file or directory''", just ignore this command since there is no '''~/.bash_profile''' file in your home directory. # Use a text editor like vi or nano to create the text file called '''~/.bash_profile''' (eg. vi ~/.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: . ~/.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 ~/.bash_profile.bk ~/.bash_profile If you experience an error message "''No such file or directory''", just ignore. # '''Exit''' your current Bash shell session. # '''Login''' again to your matrix account. What did you notice this time?

~~In the next investigation, you will ...~~= FURTHER STUDY =

~~=INVESTIGATION 3~~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 perform Linux operating 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: ~~USING STARTUP FILES =~~

~~In this section, you will learn how to ...~~

:* [https://wiki.cdot.senecacollege.ca/wiki/OPS245 OPS245: Basic Linux Server Administration]

:* [https://wiki.cdot.senecacollege.ca/wiki/OPS335 OPS335: Advanced Linux Server Administration]

~~'''Perform the Following Steps~~Take care and good luck in your future endeavours   :)

~~# x~~<brspan style="font-size:1.3em; font-family:cursive">Murray Saul

= LINUX PRACTICE QUESTIONS =

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:'''

# Write code for a Bash shell script that 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 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. # x What is the purpose of the '''/etc/profile''' startup file? # xWhat is the purpose of the '''/etc/bashrc''' startup file? # xWhat is the purpose of the '''~/.bashrc''' startup file? # xWhat is the purpose of the '''~/.bash_profile''' file? # xWhat is the purpose of the '''~/.bash_logout''' file? # xWrite 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. # xWrite 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 3Link: https://www.gnu.org/licenses/lgpl.html _________________________________________________________________________________

[[Category:ULI101]]

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