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=INTRODUCTION TO SHELL SCRIPTINGUSING SED & AWK UTILTIES=
<br>
===Main Objectives of this Practice Tutorial===
:* Plan and create Use the '''sed''' command to '''manipulate text''' contained in a Shell Scriptfile.
:* Explain the purpose of List and explain several '''addresses''' and '''instructions''' associated with the '''she-bang linesed''' contained at the top of a shell scriptcommand.
:* Set Use the '''permissionssed''' and command as a '''executefilter''' shell scriptswith Linux pipeline commands.
:* Use the '''environmentawk''' and command to '''user-definedmanipulate text''' variables contained in shell scriptsa file.
:* Use List and explain '''comparison operators''Command Substitution', '''variables''' and '''Math Operationsactions''' associated with the '''awk''' in shell scriptscommand.
:* Explain the purpose of the '''$?''' exit status and Use the '''testawk''' command. :* Use '''if''' and '''if-else''' logic statements in shell scripts. :* Use as a '''forfilter''' loop statement with a list in shell scriptsLinux pipeline commands.
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|- valign="top" style="padding-left:15px;"
|colspan="2" |Course Notes'''Slides''':<ul><li>Week 11 Lecture 1 Notes:<br> [[Media:ULI101-Week11.1.pdf | PDF]] | [https://ictmatrix.senecacollege.ca/~murraychris.sauljohnson/uli101ULI101/ULI101-Week11.1.pptx PPTX]</li><li>Week 11 Lecture 2 Notes:<br> [[Media:ULI101-Week10Week11.2.pdf | PDF]] | [https://ictmatrix.senecacollege.ca/~murrayjason.saulcarman/uli101slides/ULI101-Week10Week11.2.pptx PPTX]<br></li></ul>
| style="padding-left:15px;" |Shell Scripting'''Text Manipulation:'''* [https://searchdatacenterwww.techtargetdigitalocean.com/definitioncommunity/shelltutorials/the-basics-of-using-the-sed-stream-editor-to-manipulate-text-in-linux Purpose of using the sed utility]* [https://www.digitalocean.com/community/tutorials/how-to-use-the-awk-language-to-manipulate-text-in-script linux Purposeof using the awk utility]
|colspan="1" style="padding-left:15px;" width="30%"|'''Brauer Instructional Videos:'''<ul><li>[https://www.youtube.com/watch?v=kxEP-KUhOSgnpU6S61AIko&list=PLU1b1f-2Oe90TuYfifnWulINjMv_Wr16N&index=5 Bash Shell Scripting - Part 114 Using the sed Utility]</li><li>[https://www.youtube.com/watch?v=cQepf9fY6cE Creating and Running a Shell ScriptOV3XzjDYgJo&list=PLU1b1f-2Oe90TuYfifnWulINjMv_Wr16N&index=13 Using the awk Utility]</li></ul>
|}
= KEY CONCEPTS =
''Examples:''<br><span style="color:blue;font-weight:bold;font-family:courier;">Syntax: sed [-n] 'address instruction''chmod u+x myscript.bash<br>./myscript.bash<br>/home/username/myscript.bash<br>~/myscript.bashfilename</span>'''<br><br>
'''How it Works:'''
<br>
'''Command SubstitutionAddress:'''
<br><br>
<br>
<br>
* Action to be executed is contained within braces ''Example'{}'''* The '''print''' command can be used to display text (fields).* You can use parameters which represent fields within records (lines) within the expression of the awk utility.* The parameter '''$0''' represents all of the fields contained in the record (line).* The parameters '''$1''', '''$2''', '''$3''' … '''$9''' represent the first, second and third to the 9th fields contained within the record. * Parameters greater than nine requires the value of the parameter to be placed within braces (for example: '''${10}''','''${11}''','''${12}''', etc.)* You can use built-in '''variables''' (such as '''NR''' or "record number" representing line number)<br>eg. '''{print NR,$0}''' (will print record number, then entire record).
<span style="color:red;">'''ATTENTION''': Effective '''May 9, 2022''' - this online tutorial will be required to be completed by '''Friday in week 11 by midnight'''<br>to obtain a grade of '''2%''' towards this course</span><br><br>
'''Perform the Following Steps:'''
# '''Login''' to your matrix accountand confirm you are located in your '''home''' directory.<br><br># Issue a Linux command to create a directory called '''confirm'sed'' you are located in your '''home''' directory.<br><br>We want # Issue a Linux command to create a Bash Shell script <u>change</u> to welcome the user by their ''username'sed''' directory and confirm that you are located in the '''sed''.<br>Let's first look at selecting an appropriate filename for your shell scriptdirectory.<br><br># Issue the following linux Linux command to check if download the filename called data.txt file<br>('''hellocopy and paste'''<br>already exists as a commandto save time):<br><span style="color:blue;font-weight:bold;font-family:courier;">which hellowget <nowiki>https://ict.senecacollege.ca/~murray.saul/uli101/data.txt</nowiki></span><br><br>The output from this # Issue the '''more''' command should indicate that to quickly view the contents of the shell did NOT'''data.txt''' file.<br>find any directories that contained this filename that could representWhen finished, exit the more command by pressing the letter <br>a commandspan style="color:blue;font-weight:bold;font-family:courier; therefore, this shell script name CAN be used.<br">q<br/span>[[Image:hello0sed-1.png|thumb|right|200px300px|Using a Issuing the '''text editorp''' to add Linux commands in to instruction without using the '''hello-n''' shell scriptoption (to suppress original output) will display lines twice.]]# Use a <br><br>The '''text editorp''' like instruction with the '''vised''' or command is used to<br>'''nanoprint''' to create the text file called (i.e. '''hello'display'') the contents of a text file.<br><br># Enter Issue the following two lines in your shell scriptLinux command:<br><span style="color:blue;font-familyweight:courierbold;font-weightfamily:boldcourier;">echo<br>echo "Hello $USER"<br>echosed 'p' data.txt</span><br><br>'''NOTE:You should notice that each line appears twice''' .<br><br>The variable called reason why standard output appears twice is that the sed command<br>(without the '''USER-n option''' is ) displays all lines regardless of an address used.<br><br>We will use '''environment variablepipeline commands''' that contains to both display stdout to the screen and save to files<br>for <u>currentconfirmation</u> userof running these pipeline commands when run a 's login name''checking-script''' later in this investigation. If you wanted to share your shell script with other users, when they run <br><br># Issue the shell script, they will greeted by following Linux pipeline command:<br><uspan style="color:blue;font-weight:bold;font-family:courier;">theirsed -n 'p' data.txt | tee sed-1.txt</uspan><br><br> usernameWhat do you notice? You should see only one line. <br><br>You can specify an ''Environment variables'address' make your shell script adaptable by ALL users.'' to display lines using the sed utility<br><br>(eg. ''line # '', 'Save''line #s''' your editing session and or range of '''exitline #s''' the text editor).<br><br>Instead of issuing # Issue the '''bash''' following Linux pipeline command followed by your shell script pathname as an ''argument'',:<br>let<span style="color:blue;font-weight:bold;font-family:courier;">sed -n '1 p's simply run it by its filenamedata. This is the most common method of running shell scriptstxt | tee sed-2.txt</span><br><br>You should see the first line of the text file displayed.<table align="right"br>What other command is used to only display the first line in a file?<tr valign="top"br><tdbr>[[Image:nosed-execute2.png|thumb|right|230px500px|Using the sed command to display a '''range''' of lines.]]# Issue the following Linux pipeline command:<br><span style="color:blue;font-weight:bold;font-family:courier;">sed -n '2,5 p' data.txt |An tee sed-3.txt</span><br><br>What is displayed? How would you modify the sed command to display the line range 10 to 50?<br><br>The '''error messages''' will appear when trying instruction is used to run '''substitute''' text<br>(a shell script by name that does NOT have similar to method was demonstrated in the vi editor in tutorial 9).<br><br># Issue the following Linux pipeline command:<br><span style="color:blue;font-weight:bold;font-family:courier;">sed '2,5 s/TUTORIAL/LESSON/g' data.txt | tee sed-4.txt | more</span><br><br>What do you notice? View the original contents of lines 2 to 5 in the '''executedata.txt''' permissionsfile<br>in another shell to confirm that the substitution occurred.]]</tdbr><tdbr>[[Image:hello1sed-3.png|thumb|right|150px500px|Output from running your Using the sed command with the '''hello-q''' shell script (YourUserID representing <u>your</u> username)option to display up to a line number, then quit.]]The '''q''' instruction terminates or '''quits''' the execution of the sed utility as soon as it is read in a particular line or matching pattern.</tdbr></tablebr># Issue the following linux Linux pipeline command to run your shell script in your current directory:<br><span style="color:blue;font-weight:bold;font-family:courier;">sed '11 q' data./hellotxt | tee sed-5.txt</span><br><br>What did you notice? How many lines were displayed<br>before the sed command exited?<br><br>You should notice an can use '''ERROR message'regular expressions'' indicating you don't have permissions to run select lines that match a pattern. In fact,<br>the sed command was one of the file<u>first</u> Linux commands that used regular expression. To fix this, you need to<br><br>The rules remain the same for using regular expressions as demonstrated in '''add execute permissionstutorial 9''' prior to running <br>except the shell scriptregular expression must be contained within '''forward slashes'''<br>(eg. <span style="font-family:courier;font-weight:bold;">/regexp/</span> ).<br><br># Issue [[Image:sed-4.png|thumb|right|400px|Using the following linux sed command to using regular expressions with '''addanchors'''<br>execute permissions for your shell script.]]# Issue the following Linux pipeline command:<br><span style="color:blue;font-weight:bold;font-family:courier;">chmod u+x hellosed -n '/^The/ p' data.txt | tee sed-6.txt</span><br><br>What do you notice?<br><br># Issue the following to run your shell scriptLinux pipeline command:<br><span style="color:blue;font-weight:bold;font-family:courier;">sed -n '/d$/ p' data./hellotxt | tee sed-7.txt</span><br><br>Did your shell script runWhat do you notice?<br><br><span style="color:red;">The '''ATTENTION:sed''' Students might get FRUSTRATED when performing their utility can also be used as a '''assignment 3filter''' when their Bash shell scripts have errorsto manipulate text that<br>was generated from Linux commands.<br>One major cause is <br>[[Image:sed-5.png|thumb|right|400px|Using the the OUTPUT of their Bash shell script when run does not sed command with '''EXACTLY matchpipeline''' commands.]]# Issue the required outputfollowing Linux pipeline command:<br>for the <span style="color:blue;font-weight:bold;font-family:courier;">who | sed -n '/^[a-m]/ p''correct''' Bash shell script| tee sed-8.txt | more</span><br><br>This requires that What did you CAREFULLY notice?<br><br># Issue the following Linux pipeline command:<br><span style="color:blue;font-weight:bold;font-family:courier;">ls | sed -n '/txt$/ p''read''' the requirements of your Bash shell script and create it to the EXACT specifications| tee sed-9.txt</span><br><br>What did you notice?<br><br># Issue the following Linux command to run a checking script:<br><span style="color:blue;font-weight:bold;font-family:courier;">bash /home/murray.saul~uli101/myscripts/week10week11-check-1</span><br><br># If you encounter errors, make corrections and '''re-run''' the checking script until you<br>until you receive a congratulations message, then you can proceed.<br><br>::In the next investigation, you will learn to create and run shell scripts that<br >use '''variables''', '''positional''' and '''special parameters'''. You will also learn how to<br><u>add</u> a '''she-bang line''' at the top of a shell script to force it to run in a specified shell.<br><br>Proceed to the next investigation.<br><br>
=INVESTIGATION 2: USING THE AWK UTILITY =
In this investigation, you will learn how to use the awk utility to manipulate text and generate reports.
'''Perform the Following Steps:'''
# Confirm that Change to your '''home''' directory and issue a command to '''confirm'''<br>you are located in your '''home''' directory in your Matrix account.<br><br>Let's run shell scripts # Issue a Linux command to create a directory called '''awk'''<ubr>with</ubr> and # Issue a Linux command to <u>withoutchange</u> a to the '''she-bangawk''' line at directory and confirm you are located in the top of your shell script<br>to demonstrate why using a ''she-bang'awk''' line should be included in a shell script to forcedirectory.<br>the shell script to be run in <br>Let's download a ''specific'' shelldatabase file that contains information regarding classic cars.<br><br># Use a text editor to '''edit''' Issue the following linux command ('''hellocopy and paste''' shell script that you created in the <u>previous</u> investigation.to save time):<br><br># Add the following line to the span style="color:blue;font-weight:bold;font-family:courier;">wget <unowiki>bottomhttps://ict.senecacollege.ca/~murray.saul/uli101/cars.txt</unowiki> of the file (</span><br><br># Issue the '''copycat''' and command to quickly view the contents of the '''pastecars.txt''' to prevent ''errors''):file.<br><span style="font-family:courier;font-weight:bold;"br>echo The "The current shell you are using is: $(ps -o cmd= -p $$|cut -d' ' -f1'print'''" action (command)"is the </spanu>default<br/u>action of awk to print<br>all selected lines that match a '''FYI:pattern''' .<br><br>This command displays the '''nameaction''' of the (contained in braces) can provide more options<br>such as printing '''specific fields'shell'' that the shell script is running inof selected lines (or records) from a database.<br>The command within <span style="font-familybr>[[Image:courier;fontawk-weight:bold;">$( )</span> uses a technique known as '''command substitution'''1.<br><br># Issue png|thumb|right|400px|Using the following Linux awk command to change to display matches of the pattern '''Bourne Shellford''':<br><span style=.]]# Issue the following linux command all to display all lines (i.e. records) in the '''cars.txt''' database that matches the pattern (or "make"color:blue;) called '''ford''':<br><span style="color:blue;font-weight:bold;font-family:courier;">shawk '/ford/ {print}' cars.txt</span><br><br>You should notice your We will use '''shell prompt changedpipeline commands''' which indicates<brto both display stdout to the screen and save to files for <u>that you are confirmation</u> of running these pipeline commands when run a '''checking-script''' later in a different shellthis investigation.<br><br>[[Image:hello2.png|thumb|right|275px|Changing # Issue the following linux pipeline command all to display records<br>in the Bourne shell and running shell script '''withoutcars.txt''' a '''She-bang'database that contain the pattern (i.e. make) '' line.]]# Issue the following Linux command to run your shell script in the 'ford'Bourne Shell'':<br><span style="color:blue;font-weight:bold;font-family:courier;">awk '/ford/' cars.txt | tee awk-1./hellotxt</span><br><br>What do you notice? You should see that you are currently running the shell script "'''sh'''"notice ALL lines displayed <u>without<br/u>which represents the using '''Bourne shellsearch criteria'''.<br><br>You can use ''builtin'NOTE:''' Due to the fact that shells (and their features) have 'variables''evolved''' over a period of time,<br>an error may occur if you include a with the '''NEWER shell featureprint''' (ecommand for further processing.g. ''Bash Shell'') but run it <br>We will discuss the following variables in an '''OLDER shell''' (For examplethis tutorial: the ''Bourne Shell'').<br><br>[[Image:sheawk-bang-12.png|thumb|right|275px400px|Adding a Using the awk command to print search results by '''she-bang linefield number''' at the BEGINNING of the first line in you shell script forces the shell script to be run in that specific shell (in this case, the Bash shell).]]You can add a '''special comment$0''' called a '''she-bang Current record (entire line''' at the BEGINNING of the )<ubr>FIRST line</u> of your shell script to '''force$1''' it to run - First field in the shell you want (for example: the Bash shell).record<br><br> # Edit your '''hello''' shell script using a text editor.<br>$n''' - nth field in record<br># '''InsertNR''' the following line at the - Record Number (order in database)<br> '''beginningNF''' - Number of the '''first''' line fields in current record<br><br>For a listing of more variables, please consult your hello file:course notes.<br><span style="font-family:courier;font-weight:bold;">#!/bin/bash</span><br><br>This is referred to as a br># Issue the following linux pipeline command to display the '''model''', '''year''', '''quantity'she-bang line'''. It forces this script to be run and price<br>in the '''Bash Shellcars.txt'''.<br>When your Bash Shell script finishes execution, you are returned to your current shell that you are using (which in our case in Matrix, is still the Bash shell).database for makes of '''chevy''':<br><br>[[Imagespan style="color:hello3.png|thumb|right|275px|Changing the Bourne shell and running shell script '''with''' a '''Sheblue;font-bangweight:bold;font-family:courier;">awk '/chevy/ {print $2,$3,$4,$5}'' line (forcing script to run in the cars.txt | tee awk-2.txt</span><br><br>Notice that a '''Bashspace''' shell)is the delimiter for the fields that appear as standard output.]]# <br><br>The '''Savetilde character''' your editing changes and '''exit~''' your text editoris used to search for a pattern or display standard output for a particular field.<br><br># While in the Bourne shell, issue Issue the following Linux linux pipeline command:<br><span style="color:blue;font-weight:bold;font-family:courier;">./hello</span>to display all '''plymouths''' ('''plym''')<br><br>You should notice that the shell by '''model name is running in the '''Bash shell, '''price'.<br><br> # It is a good idea to rename your shell script to include an ''and 'extension''quantity' to<br>explain that this is '''Bash Shell script''' file (referred to as a "''portable Bash shell script''"). :<br>Issue the following Linux command to rename your shell script file:<br><span style=<span style="color:blue;font-weight:bold;font-family:courier;">mv hello hello.bash<awk '$1 ~ /plym/span><br><{print $2,$3,$4,$5}' cars.txt | tee awk-3.txt</span><br># Confirm that the modification work by running your Bash shell script:<br><span style="color:blue;font-weight:bold;font-family:courier;">./hello.bash</span>You can also use '''comparison operators''' to specify conditions for processing with matched patterns<br><br># Enter when using the following Linux awk command to '''exit''' . Since they are used WITHIN the ''Bourne shell'' and return to your ''Bash shell'':awk expression,<br>they are not confused with redirection symbols<span style="color:blue;font-weight:bold;font-family:courier;">exit</span>br><br><br>Let[[Image:awk-3.png|thumb|right|400px|Using the awk command to display results based on '''comparison operators''s use some '.]]'''ENVIRONMENT variables<''' in our Bash Shell script. Less than<br>'''<=''' Less than or equal<br># Use a text editor to edit the shell script called '''hello.bash>''' Greater than<br>'''>=''' Greater than or equal<br># Add the following lines to the '''==''' Equal<ubr>bottom</u> of the ''hello.bash'!=''' file: Not equal<br><span style="font-family:courier;font-weight:bold;">echo<br>echo "The current directory location is: $PWD"<br>echo "The current user home directory is: $HOME"<br>echo</span># Issue the following linux pipeline command to display display the '''car make''', '''model''', '''quantity''' and '''price''' of all vehicles whose '''prices are less than $5,000''':<br><br># Save your editing changes and exit your text editor.<br><br>[[Imagespan style="color:blue;font-weight:hello4bold;font-0.png|thumbfamily:courier;">awk '$5 < 5000 {print $1,$2,$4,$5}' cars.txt |right|330px|Running tee awk-4.txt<u/span>modified</ubr> <br>What do you notice?<br><br># Issue the following linux pipeline command to display display '''price''hello.bash'' Bash shell script by using relative pathname: ,<span style="font-family:courier;">br>'''quantity'./hello.bash''</span>]]# To confirm that you properly renamed your shell script,<br>run the following shell script'''model''' and '''car make''' of vehicles whose '''prices are less than $5,000''':<br><span style="color:blue;font-weight:bold;font-family:courier;">./hello.bashawk '$5 </5000 {print $5,$4,$2,$1}' cars.txt | tee awk-5.txt</span><br><br>Take time # Issue the following linux pipeline command to view display the output and the values of the environment variables.'''car make''',<br><br># Issue the following Linux command to add your current directory to the '''PATHyear''' and '''quantity' environment variable:<br><'' of cars that '''begin''' with the '''letter 'f'''':<br><span style="color:blue;font-weight:bold;font-family:courier;">PATH=awk '$PATH:.<1 ~ /^f/span{print $1,$2,$4}' cars.txt | tee awk-6.txt</span><br><br>[[Image:hello4awk-4.png|thumb|right|330px400px|Running <u>modified</u> Using the awk command to display combined search results based on '''compound operators'hello.bash'' Bash shell script .]]Combined pattern searches can be made<br>by entering using '''compound operator''' symbols:<ubr>just</ubr> '''filename&&''' (i.e. and)<span style="font-family:courier;">br>'''||'hello.bash'' (or)</spanbr> and NOT <span style="font-family:courier;">''./hello.bash''</span> shown in previous diagram).]]br># Issue the following Linux linux pipeline command to confirm that the current directory list all '''fords'"."''<br>whose ' has been added to the '''PATHprice is greater than $10,000''' environment variable:<br><span style="color:blue;font-weight:bold;font-family:courier;">echo awk '$1 ~ /ford/ && $5 > 10000 {print $PATH0}' cars.txt | tee awk-7.txt</span><br><br># Issue the following to run your Bash shell script just by namelinux command ('''copy and paste''' to save time):<br><span style="color:blue;font-weight:bold;font-family:courier;">hellowget <nowiki>https://ict.bashsenecacollege.ca/~murray.saul/uli101/cars2.txt</spannowiki><br/span><br>Did your Bash shell script run?<br><br># Exit your Matrix session, and log back into your Matrix sessionIssue the '''cat''' command to quickly view the contents of the '''cars2.txt''' file.<br><br># Re-run Issue the following linux pipeline command to display the '''hello.bash'year''' shell script by just using the name.<br><br>What did you notice?<br><br>The setting of the and '''PATHquantity''' environment variable only worked in the current session onlyof cars that '''begin''' with the '''letter 'f'''' for the '''cars2.txt''' database:<br>If you exit the current Matrix session<span style="color:blue;font-weight:bold;font-family:courier;">awk '$1 ~ /^f/ {print $2, then the recently changed settings for environment variables will be lost.<br>You will in a <u>future$4}' cars2.txt | tee awk-8.txt</uspan> tutorial how to set environment variables in '''start-up''' files.<br><br><span style="color:red;"What did you notice?<br><br>The problem is that the '''ATTENTION:cars2.txt''' Students will get FRUSTRATED when performing their database separates each field by a semi-colon ('''assignment 3;''' when their Bash shell scripts have errors. One major cause is that the OUTPUT of <) <u>yourinstead</u> Bash shell script does NOT match the of '''required outputTAB''' of .<br>Therefore, it does not recognize the assignment checking programsecond and fourth fields. This requires that you CAREFULLY '''read''' <br><br>You need to issue awk with the requirements of your Bash shell script -F option to match the EXACT specifications</span>indicate that this file's fields are separated (delimited) by a semi-colorn.<br><br># Issue the following Linux linux pipeline command to run a checking script:display the '''year'''<br><span style="color:blue;font-weightand '''quantity''' of cars that '''begin''' with the '''letter 'f'''' for the '''cars2.txt''' database:bold;font-family:courier;"<br>bash /home/murray.saul/myscripts/week10<span style="color:blue;font-checkweight:bold;font-2 | more</span><br><brfamily:courier;">If you encounter errorsawk -F";" '$1 ~ /^f/ {print $2, make corrections and $4}'''recars2.txt | tee awk-run''' the checking script until you9.txt</span><br><br>receive a congratulations message, then What did you can proceed.notice this time?<br><br>Let's create # Issue the following to run a Bash shell checking script that contain '''user-created variables'''.:<br><br># Use a text editor to create a Bash shell script called '''userspan style="color:blue;font-weight:bold;font-family:courier;">~uli101/week11-check-variables.bash'''2</span><br><br># Add the following lines to the beginning of the If you encounter errors, make corrections and '''userre-variables.bashrun''' file:the checking script until you<br><span style="font-family:courier;font-weight:bold;">#!/bin/bash<br>read -p "Enter your Full Name: " name<br>read -p "Enter your age (in years): " age<br>echo "Hello $name - You are $age years old"</span><br><br># Save your editing changes and exit your text editor.<br><br>[[Image:user-variable1.png|thumb|right|300px|Prompting user to enter data via the '''read -p''' command storing into '''user-created variable'''.]]# Issue the '''chmod''' command to add '''execute permissions''' for the user for the '''user-variables.bash''' file.<br><br># Issue the following to run the user-variables.bash Bash shell script<br> (enter your Full name and age when prompted):<br><span style="color:blue;font-weight:bold;font-family:courier;">./user-variables.bash</span><br><br>What did you notice?<br><br># Use a text editor to '''modify''' your Bash shell script called '''user-variables.bash'''<br><br># '''Insert''' the following lines immediately <u>'''below'''</u> the '''she-bang''' line:<br><span style="font-family:courier;font-weight:bold;">age=25<br>readonly age</span><br><br># Save your editing changes and exit your text editor.<br><br>[[Image:user-variable2.png|thumb|right|330px|Trying to change the value of a '''read-only''' variable'''.]]# Issue the following to run the user-variables.bash Bash shell script:<br><span style="color:blue;font-weight:bold;font-family:courier;">./user-variables.bash</span><br><br>What do you notice when you try to change the age variable? Why?<br><br>Let's use '''positional parameters''' and '''special parameters''' in a Bash shell script.<br><br># Use a text editor to create a file called '''parameters.bash'''<br><br># Add the following lines to the beginning of this file:<br><span style="font-family:courier;font-weight:bold;">#!/bin/bash<br>echo \$0: $0<br>echo \$2: $2<br>echo \$3: $3<br><br>echo \$#: $#<br>echo \$*: $*<br><br>shift 2<br>echo \$#: $#<br>echo \$*: $*</span><br><br># Save your editing changes and exit your text editor.<br><br>Notice how the quoting character "'''\'''" is used to display positional parameters like "'''$2'''"<br>as opposed to the value stored in the <u>second</u> positional parameter.<br><br># Issue the '''chmod''' command to add '''execute permissions''' for the user for the '''parameters.bash''' file.<br><br>[[Image:parameter1.png|thumb|right|250px|Results from running shell script (with arguments) that use '''positional parameters''' and '''special parameters'''.]]# Issue the following to run the '''user-variables.bash''' Bash shell script:<br><span style="color:blue;font-weight:bold;font-family:courier;">./parameters.bash</span><br><br>What happened?<br><br>The values for some of the ''positional parameters'' and ''special parameters'' may NOT be<br>displayed properly since you did NOT provide any '''arguments''' when <u>running</u> your Bash shell script.<br><br># Issue the following to run the user-variables.bash Bash shell script with arguments:<br><span style="color:blue;font-weight:bold;font-family:courier;">receive a congratulations message, then you can proceed./parameters.bash 1 2 3 4 5 6 7 8</span><br><br>What do you notice?<br><br>Take some time to view the results and how the ''parameters'' have changed when using the '''shift''' command. <br>
= LINUX PRACTICE QUESTIONS =
https://ict.senecacollege.ca/~murray.saul/uli101/uli101_week11_practice.docx
''For example'Review Questions:'''
Note the contents from the following tab-delimited file called '''~murray.saul/uli101/stuff.txt''':
(this file pathname exists for checking your work)
'''Perform Part B: Writing Linux Commands Using the Following Steps:sed Utility'''
'''Perform the Following Steps:'''<br><br>: You can test conditions by issuing '''Linux commands / pipeline commands''' and by using the '''test''' command.<br><br># Confirm that you are located in your '''home''' directory in your Matrix account.<br><br># Issue the following Linux commands at the Bash shell prompt to assign values to several variables:<br><span style="color:blue;font-weight:bold;font-family:courier;">course="ULI101"<br>number1=5<br>number2=10</span><br><br># Issue the following Linux command to test a condition:<br><span style="color:blue;font-weight:bold;font-family:courier;">test $course = "ULI101"</span><br><br>The '''$?''' variable is used to store an '''exit status''' of the <u>previously-issued</u> command (including the test command).<br>If the exit status is '''zero''', then it indicates a TRUE value and if the status is '''non-zero''', then it indicates a FALSE value.<br><br># Issue the following Linux command to view the status of the previously-issued '''test''' command:<br><span style="color:blue;font-weight:bold;font-family:courier;">echo $?</span><br><br>Based on the ''exit status'' value, is the result TRUE or FALSE?<br><br># Issue the following Linux command to test another condition:<br><span style="color:blue;font-weight:bold;font-family:courier;">test $course = "uli101"</span><br><br># Issue the following Linux command to view the status of the previously-issued '''test''' command:<br><span style="color:blue;font-weight:bold;font-family:courier;">echo $?</span><br><br>Based on the ''exit status'' value, is the result TRUE or FALSE?<br>The value is non-zero (FALSE) since UPPERCASE characters<br>are different than lowercase characters.<br><br># Issue the following Linux command to test another condition:<br><span style="color:blue;font-weight:bold;font-family:courier;">test $course != "uli101"</span><br><br># Issue a linux command to display the value of '''$?'''<br><br>What is the result? Why?<br><br># Issue the following Linux command to test a condition involving earlier assigned variables:<br><span style="color:blue;font-weight:bold;font-family:courier;">test $number1 > $number2</span><br><br># Issue a Linux command to display the value of '''$?'''<br><br>'''NOTE:''' You will notice that something is '''wrong'''.<br>The exit status '''$?''' shows a zero (TRUE) value, but the number 5 is definitely NOT greater than 10.<br>The problem is that the symbols '''<''' and '''>''' are interpreted as REDIRECTION symbols!<br><br># To prove this, issue the following Linux command :<br><span style="color:blue;font-weight:bold;font-family:courier;">ls -l 10</span><br><br>You should notice a file called "'''10'''". The incorrectly issued '''test''' command used redirect to create an empty file instead,<br> which indeed succeeded just giving a TRUE value!<br><br>To prevent problems when issuing the '''test''' command when comparing numbers, you can use the following options:<br>'''-lt''' (<), '''-le''' (<=), '''-gt''' (>), '''-ge''' (>=;), '''-eq''' (=), '''-ne''' (!=)<br><br># Issue the correct Linux command to properly test both values:<br><span style="color:blue;font-weight:bold;font-family:courier;">test $number1 -gt $number2</span><br><br># Issue a Linux command to display the value of '''$?'''.<br><br>You should notice that the exit status value is now FALSE which is the correct result.<br><br># The '''test''' command can be abbreviated by the square brackets '''[ ]''' which contains the '''test''' condition<br>within the square brackets. You need to have spaces between the brackets and the test condition;<br>otherwise, you will get a test error.<br><br># To generate a '''test error''', copy and paste the following '''test''' command:<br><span style="color:blue;font-weight:bold;font-family:courier;">[$number1 -gt $number2]</span><br><br>The reason for the error was that you need '''spaces''' between the '''square brackets''' and the '''test condition'''.<br><br># Copy and paste the following (correct) '''test''' command:<br><span style="color:blue;font-weight:bold;font-family:courier;">[ $number1 -gt $number2 ]</span><br><br># Issue a command to view the value of the '''exit status''' of the previously issued '''test''' command.<br>You should notice that is works properly.<br><br>Now that we have learned how to test conditions, let's learn about '''control-flow''' statements.<br><br>'''Logic statements''' are used to create '''different paths''' or directions that the shell script will take<br>based on the <u>result</u> of the '''test condition'''. In this tutorial,<br>we will only focus on the '''if''' and '''if-else''' logic statement.<br><br># Use a text editor like vi or nano to create the text file called '''if-1.bash''' (eg. <span style="color:blue;font-weight:bold;font-family:courier;">vi if-1.bash</span>)<br><br># Enter the following lines in your shell script:<br><span style="font-family:courier;font-weight:bold;">#!/bin/bash<br>num1=5<br>num2=10<br>if [ $num1 -lt $num2 ]<br>then<br> echo "num1 is less than num2"<br>fi</span><br><br># Save your editing session and exit the text editor (eg. with vi: press '''ESC''', then type ''':wx''' followed by '''ENTER''').<br><br>[[Image:if-1.png|thumb|right|200px|Output of a shell script using the '''if''' control-flow statement.]]# Issue the following Linux command to add execute permissions for your shell script:<br><span style="color:blue;font-weight:bold;font-family:courier;">chmod u+x if-1.bash</span><br><br># Run your shell script by issuing: <span style="color:blue;font-weight:bold;font-family:courier;">./if-1.bash</span><br><br>Confirm that the output indicated a correct result.<br><br># Use a text editor like vi or nano to create the text file called '''if-2.bash''' (eg. <span style="color:blue;font-weight:bold;font-family:courier;">vi if-2.bash</span>)<br><br>If you are using the nano text editor, refer to notes on text editing in a previous week in the course schedule.<br><br># Enter the following lines in your shell script:<br><span style="font-family:courier;font-weight:bold;">#!/bin/bash<br>read -p "Enter the first number: " num1<br>read -p "Enter the second number: " num2<br>if [ $num1 -gt $num2 ]<br>then<br> echo "The first number is greater than the second number."<br>fi</span><br><br># Save your editing session and exit the text editor (eg. with vi: press '''ESC''', then type ''':wx''' followed by '''ENTER''').<br><br>[[ImagePart C:if-2.png|thumb|right|320px|Output of a shell script using the '''read''' command '''if''' control-flow statement.]]# Issue the following Writing Linux command to add execute permissions for your shell script:<br><span style="color:blue;font-weight:bold;font-family:courier;">chmod u+x if-2.bash</span><br><br># Run your shell script by issuing: <span style="color:blue;font-weight:bold;font-family:courier;">./if-2.bash</span><br><br>Confirm that the output indicated a correct result.<br><br>What happens when you enter a first number that is less than or equal to the second number? Let's use an '''if-else''' statement to provide an appropriate alternative<br>if the condition is FALSE.<br><br># Use a text editor like vi or nano to create the text file called '''if-3.bash''' (eg. <span style="color:blue;font-weight:bold;font-family:courier;">vi if-3.bash</span>)<br><br># Enter Commands Using the following lines in your shell script:<br><span style="font-family:courier;font-weight:bold">#!/bin/bash<br>read -p "Enter the first number: " num1<br>read -p "Enter the second number: " num2<br>if [ $num1 -gt $num2 ]<br>then<br> echo "The first number is greater than the second number."<br>else<br> echo "The first number is less than or equal to the second number."<br>fi</span><br><br># Save your editing session and exit the text editor (eg. with vi: press '''ESC''', then type ''':wx''' followed by '''ENTER''').<br><br>[[Image:if-3.png|thumb|right|330px|Output of a shell script using the '''if-else''' control-flow statement.]]# Issue the following Linux command to add execute permissions for your shell script:<br><span style="color:blue;font-weight:bold;font-family:courier;">chmod u+x if-3.bash</span><br><br># Run your shell script by issuing: <span style="color:blue;font-weight:bold;font-family:courier;">./if-3.bash</span><br><br>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.<br><br>Let's learn how to use a '''loop''' with shell scripting. In this tutorial, we will only focus on one simple use with the '''for''' loop.<br><br># Use a text editor like vi or nano to create the text file called '''for-1.bash''' (eg. <span style="color:blue;font-weight:bold;font-family:courier;">vi for-1.bash</span>)<br><br># Enter the following lines in your shell script:<br><span style="font-family:courier;font-weight:bold;">#!/bin/bash<br>echo<br>for x in 5 4 3 2 1<br>do<br> echo $x<br>done<br>echo "blast-off!"<br>echo</span><br><br># Save your editing session and exit the text editor (eg. with vi: press '''ESC''', then type ''':wx''' followed by '''ENTER''').<br><br>[[Image:for-1.png|thumb|right|125px|Output of a shell script using the '''for''' loop with a '''list'''.]]# Issue the following Linux command to add execute permissions for your shell script:<br><span style="color:blue;font-weight:bold;font-family:courier;">chmod u+x for-1.bash</span><br><br># Run your shell script by issuing: <span style="color:blue;font-weight:bold;font-family:courier;">./for-1.bash</span><br><br># Use a text editor like vi or nano to create the text file called '''for-2.bash''' (eg. <span style="color:blue;font-weight:bold;font-family:courier;">vi for-2.bash</span>)<br><br># Enter the following lines in your shell script:<br><span style="font-family:courier;font-weight:bold;">#!/bin/bash<br>echo<br>for x<br>do<br> echo $x<br>done<br>echo "blast-off!"<br>echo</span><br><br># Save your editing session and exit the text editor (eg. with vi: press '''ESC''', then type ''':wx''' followed by '''ENTER''').<br><br># Issue the following Linux command to add execute permissions for your shell script:<br><span style="color:blue;font-weight:bold;font-family:courier;">chmod u+x for-2.bash</span><br><br>[[Image:for-2.png|thumb|right|175px|Output of a shell script using the '''for''' loop <u>without</u> a '''list'''.]]# Run your shell script by issuing: <span style="color:blue;font-weight:bold;font-family:courier;">./for-2.bash 10 9 8 7 6 5 4 3 2 1</span><br><br>How does this differ from the previous shell script?<br><br>You will learn in a couple of weeks more examples of using loop statements.<br><br>Let's run a '''checking-script''' to confirm that both your '''for-1.bash''' and '''for-2.bash'''<br>Bash shell scripts exist, have execute permissions, and when run, produce<br>the same OUTPUT as required in this tutorial's instructions.<br><br># Issue the following Linux command to run a checking script:<br><span style="color:blue;font-weight:bold;font-family:courier;">bash /home/murray.saul/myscripts/week10-check-4 | more</span><br><br>If you encounter errors, make corrections and '''re-run''' the checking script until you<br>receive a congratulations message, then you can proceed.<br><br># After you complete the Review Questions sections to get additional practice, then work on your '''online assignment 3''',<br>'''sections 2 and 3''' labelled '''Interactive Shell Environment''' and '''Introduction To Scripting (phone)awk Utility'''.<br><br>
<pre>
Line one.
This is the second line.
This is the third.
This is line four.
Five.
Line six follows
Followed by 7
Now line 8
and line nine
Finally, line 10
</pre>
'''Write the results of each of the following Linux commands for the above-mentioned file:'''
# Write a Linux awk command to display all records for the file:'''cat walkthru1~/cars''' whose fifth field is greater than 10000.bash<br><br># Write a Linux awk command to display the first and fourth fields for the file: '''~/cars''' whose fifth field begins with a number.<br><prebr>#!Write a Linux awk command to display the second and third fields for the file: '''~/usr/bin/bashcars''' for records that match the pattern “chevy”.<br><br>word1=”counter”word2=”clockwise”echo “The combined word is# Write a Linux awk command to display the first and second fields for all the records contained in the file: $word2$word1”'''~/cars'''<br></prebr>
[[Category:ULI101]]