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=INTRODUCTION TO SHELL SCRIPTINGUSING SED & AWK UTILTIES=
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===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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|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:'''
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* 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$/ p''read''' the requirements of your Bash shell script and create it to the EXACT specifications| tee sed-9.txt</span><br><br>What did you notice?<br><br># Issue the following Linux command to run a checking script:<br><span style="color:blue;font-weight:bold;font-family:courier;">bash /home/murray.saul~uli101/myscripts/week10week11-check-1</span><br><br># If you encounter errors, make corrections and '''re-run''' the checking script until you<br>until you receive a congratulations message, then you can proceed.<br><br>::In the next investigation, you will learn to create and run shell scripts that<br >use '''variables''', '''positional''' and '''special parameters'''. You will also learn how to<br><u>add</u> a '''she-bang line''' at the top of a shell script to force it to run in a specified shell.<br><br>Proceed to the next investigation.<br><br>
In this investigation, you will learn how to use the awk utility to manipulate text and generate reports.
'''Perform the Following Steps:'''
# Confirm that Change to your '''home''' directory and issue a command to '''confirm'''<br>you are located in your '''home''' directory in your Matrix account.<br><br>Let's demonstrate that the Unix/Linux shell stores numbers as ascii text<br>which can cause problems when performing math operations.# Issue a Linux command to create a directory called '''awk'''<br><br># Issue the following a Linux command from the shell:to <bru>change<span style="color:blue;font-family:courier;font-weight:bold">echo "1 + 2"</span>/u> to the '''awk''' directory and confirm you are located in the '''awk''' directory.<br><br>What did you notice?Let's download a database file that contains information regarding classic cars.<br><br># To demonstrate Issue the need for the '''following linux command (( ))''' construct, issue the following Linux commands (using the copy and paste''math construct''to save time):<br><span style="color:blue;font-familyweight:courierbold;font-weightfamily:boldcourier;">echo "$((1 + 2))"wget <nowiki>https:/span><br/ict.senecacollege.ca/~murray.saul/uli101/cars.txt</nowiki><br/span>What did you notice?<br>The <span style="font-family:courier;font-weight:bold"br>(( ))</span> construct converted values # Issue the '''1cat''' and '''2''' from ''text'' command to quickly view the contents of the '''binary numberscars.txt'''file.<br><br>The "'''$print''' in front " action (command) is the <u>default</u> action of the construct awk to print<br>all selected lines that match a '''expandspattern''' the result of the calculation.<br><br># Issue the following Linux commands demonstrating other types This '''action''' (contained in braces) can provide more options<br>such as printing '''specific fields''' of math calculations:selected lines (or records) from a database.<br><span style="colorbr>[[Image:blue;fontawk-family:courier;font-weight:bold">echo "$((2 - 3))1.png|thumb|right|400px|Using the awk command to display matches of the pattern '''ford'''.]]# Issue the following linux command all to display all lines (i.e. records) in the '''cars.txt''' database that matches the pattern (or "</span>make") called '''ford''':<br><span style="color:blue;font-familyweight:courierbold;font-weightfamily:boldcourier;">echo "$((2 * 3))"awk '/ford/ {print}' cars.txt</span><br><span style="color:blue;font-family:courier;font-weight:bold"br>We will use '''pipeline commands''' to both display stdout to the screen and save to files for <u>echo "$((2 / 3))"confirmation</u> of running these pipeline commands when run a '''checking-script''' later in this investigation.</spanbr><br># Issue the following linux pipeline command all to display records<span style="color:blue;font-family:courier;font-weight:bold">echo "$((2 ** 3))"</span><br><brbr>in the '''NOTE:cars.txt''' You may notice database that contain the pattern (i.e. make) '''dividingford''' :<br><span style="color:blue;font-weight:bold;font-family:courier;">awk '/ford/''2''' by '''3''' shows a '''zero''' resultcars.txt | tee awk-1. To perform decimal calculations would requiretxt</span><br>the use the <br>What do you notice? You should notice ALL lines displayed <u>without</u> using '''awksearch criteria''' or .<br><br>You can use ''builtin'bc''' Linux commands (we will 'variables''NOT'with the '' cover that method to work with 'print'decimal numbers'' in this course)command for further processing.<br><br>You can use We will discuss the ''math construct'' with following variables as well.in this tutorial:<br><br># Issue the following Linux commands demonstrating using [[Image:awk-2.png|thumb|right|400px|Using the awk command to print search results by '''field number'math construct'' with .]]'''variables$0''':- Current record (entire line)<br><span style="color:blue;font'''$1''' -family:courier;font-weight:bold">num1=34First field in record</spanbr>'''$n''' - nth field in record<br><span style="color:blue;font'''NR''' -family:courier;font-weight:bold">num2=12</span>Record Number (order in database)<br><span style="color:blue;font'''NF''' -family:courier;font-weight:bold">echo "$((num1 * num2))"</span>Number of fields in current record<br><br>What did you notice?<br><br>You can create For a listing of more variables and assign them values in the ''math construct'' as well, please consult your course notes.<br><br># Issue the following Linux commands demonstrating using linux pipeline command to display the math construct with '''variablesmodel''', ':<br''year''', '''quantity''' and price<br>in the '''cars.txt''' database for makes of '''chevy''':<br><span style="color:blue;font-familyweight:courierbold;font-weightfamily:boldcourier;">num1=awk '/chevy/ {print $2,$3,$4,$5}' cars.txt | tee awk-2.txt</span><br><span style="color:blue;font-family:courier;font-weight:bold">num2=3br>Notice that a '''space''' is the delimiter for the fields that appear as standard output.</spanbr><br>The '''tilde character''' '''~''' is used to search for a pattern or display standard output for a particular field.<span style="color:blue;font-family:courier;font-weight:bold">((result = num1 ** num2))</spanbr><br># Issue the following linux pipeline command to display all '''plymouths''' ('''plym''')<span style=br>by '''model name''', '''price''' and '''quantity''':<br><span style="color:blue;font-familyweight:courierbold;font-weightfamily:boldcourier;">echo "The result is: awk '$1 ~ /plym/ {print $2,$3,$4,$result"5}' cars.txt | tee awk-3.txt</span><br><br># Use a text editor to create a Bash shell script called You can also use '''dog-years.bashcomparison operators'''to specify conditions for processing with matched patterns<br>when using the awk command. Since they are used WITHIN the awk expression,<br># Add the following lines to the beginning of this file:they are not confused with redirection symbols<br><span style="font-familybr>[[Image:courier;fontawk-weight:bold;">#!/bin/bash<br>echo<br>dogFactor=73.png|thumb|right|400px|Using the awk command to display results based on '''comparison operators'''.]]'''<''' Less than<br>read -p "Please enter your age (in years): " humanYears<br>((dogYears '''<= humanYears * dogFactor))''' Less than or equal<br>echo "You age in dog-years is: $dogYears"<br'''>echo<''' Greater than<br></span'''>=''' Greater than or equal<br># Save your editing changes and exit your text editor.'''==''' Equal<br><br>[[Image:mathops1.png|thumb|right|275px|Output of a shell script with math operations using the '''math construct!='''.]] Not equal<br><br># Issue the following linux pipeline command to display display the '''chmodcar make''' command to add execute permissions<br>for the user for the , '''dog-years.bashmodel''' file.<br><br># Issue the following to run the , '''quantity''' and '''price''user-variables.bash'of all vehicles whose '' Bash shell script:<br><span style='prices are less than $5,000''':<br><span style="color:blue;font-weight:bold;font-family:courier;">awk '$5 < 5000 {print $1,$2,$4,$5}' cars./dogtxt | tee awk-years4.bashtxt</span><br><br>Enter <u>your</u> age to see what happens.What do you notice?<br><br># Issue the following linux pipeline command to run a checking script:display display '''price''',<br><span style'''quantity''', '''model''' and '''car make''' of vehicles whose '''prices are less than $5,000''':<br><span style="color:blue;font-weight:bold;font-family:courier;">bash /home/murrayawk '$5 < 5000 {print $5,$4,$2,$1}' cars.saul/myscripts/week10txt | tee awk-check-3 | more5.txt</span><br><br>If you encounter errors, make corrections and # Issue the following linux pipeline command to display the '''re-runcar make''' the checking script until you<br>receive a congratulations message, then you can proceed.<br><br> :In '''year''' and '''quantity''' of cars that '''begin''' with the next investigation, you will use '''control-flow statementsletter 'f'''' to allow your shell scripts:<br>to perform differently under different situations.<br><br> =INVESTIGATION 4span style="color:blue;font-weight:bold;font-family: CONTROL FLOW STATEMENTS =<brcourier;">In this investigation, you will learn how to use awk '$1 ~ /^f/ {print $1,$2,$4}''controlcars.txt | tee awk-flow statements'''6.txt</span><br><br>to make your shell script ''behave differently'' under [[Image:awk-4.png|thumb|right|400px|Using the awk command to display combined search results based on ''different situations or conditions'compound operators'''. ]]Combined pattern searches can be made<br>by using '''Perform the Following Steps:compound operator'''symbols:<br><br># Confirm that you are located in your '''home&&'''' directory in your Matrix account. (and)<br><br>'''||''' (or)<br><br># Issue the following Linux commands at the Bash shell prompt linux pipeline command to assign values to several variableslist all '''fords'''<br>whose '''price is greater than $10,000''':<br><span style="color:blue;font-weight:bold;font-family:courier;">course="ULI101"<br>number1=awk '$1 ~ /ford/ && $5<br>number2=1010000 {print $0}' cars.txt | tee awk-7.txt</span><br><br>You can test conditions by issuing # Issue the following linux command ('''Linux commands / pipeline commandscopy and paste''' to save time):<ubr>or</uspan style="color:blue;font-weight:bold;font-family:courier;">wget <brnowiki>by using the '''testhttps://ict.senecacollege.ca/~murray.saul/uli101/cars2.txt</nowiki></span><br><br># Issue the '''cat''' command. We will demonstrate using to quickly view the contents of the '''testcars2.txt''' command in this tutorial,<br>and then we will demonstrate how to test by issuing a ''Linux command / pipeline command'' in a <u>later</u> tutorialfile.<br><br># Issue the following Linux linux pipeline command to test a condition:display the '''year'''<br><span style="color:blue;font-weight:bold;font-family:courier;">test $course = "ULI101"</span><br><br>The and '''quantity''' of cars that '''begin''' with the '''letter 'f'$?''' variable is used to store an for the '''exit statuscars2.txt''' of the database:<ubr>previously<span style="color:blue;font-weight:bold;font-issued</ufamily:courier;"> command (including the test command).<br>If the exit status is '''zero''awk '$1 ~ /^f/ {print $2, then it indicates a $4}''TRUE'' value and if the status is '''noncars2.txt | tee awk-zero''', then it indicates a ''FALSE'' value8.txt</span><br><br>What did you notice?<br><br># Issue the following Linux command to view The problem is that the '''exit statuscars2.txt''' of the previouslydatabase separates each field by a semi-issued colon ('''test;''' command:) <bru><span style="color:blue;font-weight:bold;font-family:courier;">echo $?instead</spanu><br><br>Based on the of '''exit statusTAB'' value, is the result ''TRUE'' or ''FALSE''?.<br>Therefore, it does not recognize the second and fourth fields.<br># Issue the following Linux command to test another condition:<br><span style="color:blue;fontYou need to issue awk with the -weight:bold;fontF option to indicate that this file's fields are separated (delimited) by a semi-family:courier;">test $course = "uli101"colorn.</span><brbr><br># Issue the following Linux linux pipeline command to view display the ''exit status'year'''<br>and '''quantity''' of cars that '''begin''' with the previously-issued '''testletter 'f'''' command:<br>for the '''cars2.txt''' database:<br><span style="color:blue;font-weight:bold;font-family:courier;">echo awk -F";" '$?1 ~ /^f/ {print $2,$4}' cars2.txt | tee awk-9.txt</span><br><br>Based on the ''exit status'' value, is the result TRUE or FALSEWhat did you notice this time?<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 conditionrun a checking script:<br><span style="color:blue;font-weight:bold;font-family:courier;">test $course != "~uli101"/week11-check-2</span><br><br># Issue a linux command to display the value of If you encounter errors, make corrections and '''$?re-run'''<br><br>What is the result? Why?checking script until you<br><br># Issue the following Linux command to test receive 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 redirection'''<br>to create an '''empty''' file and assigning the exit status variable a ''TRUE'' value!<br><br>To prevent problems when issuing the '''test''' command when comparing numbers,<br>you can use the following '''test 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 substituted by '''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,we will only focus on the '''if''' and '''if-else''' logic statements.<br><br># Use a text editor like vi or nano to create the text file called '''if-1.bash'''<br>(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<br>(eg. with vi: press '''ESC''', then type ''':x''' 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:<br><span style="color:blue;font-weight:bold;font-family:courier;">./if-1.bash</span><br><br>Confirm that the output indicates a correct result.<br><br># Use a text editor like vi or nano to create the text file called '''if-2.bash'''<br>(eg. <span style="color:blue;font-weight:bold;font-family:courier;">vi if-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>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<br>(eg. with vi: press '''ESC''', then type ''':x''' followed by '''ENTER''').<br><br>[[Image:if-2.png|thumb|right|320px|Output of a shell script using the '''read''' command and 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-2.bash</span><br><br># Run your shell script by issuing:<br><span style="color:blue;font-weight:bold;font-family:courier;">./if-2.bash</span><br><br>When prompted, make certain that the '''first number'''<br>is <u>greater than</u> the '''second number'''. What happens?<br><br># Run the <span style="font-weight:bold;font-family:courier;">./if-2.bash</span> Bash shell script again.<br><br> When prompted, make certain that the '''first number'''<br>is <u>less than or equal to</u> the '''second number'''. What happens?<br><br>Let's use an '''if-else''' statement to provide an '''alternative'''<br>if the first number is less than or equal to the second number.<br><br># Use a text editor like vi or nano to create the text file called '''if-3.bash'''<br>(eg. <span style="color:blue;font-weight:bold;font-family:courier;">vi if-3.bash</span>)<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>else<br> echo "The first number is less than or equal to the second number."<br>fi</span><br><br>[[Image:if-3.png|thumb|right|330px|Output of a shell script using the '''if-else''' control-flow statement.]]# Save your editing session and exit the text editor<br>(eg. with vi: press '''ESC''', then type ''':x''' 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 if-3.bash</span><br><br># Run your shell script by issuing:<br><span style="color:blue;font-weight:bold;font-family:courier;">./if-3.bash</span><br><br>Try running the script several times with numbers '''different''' and '''equal'''<br>to each other to confirm that the shell script works correctly.<br><br>'''LOOP STATEMENTS''' are a series of steps or sequence of statements executed<br>repeatedly zero or more times satisfying the given condition is satisfied.''<br>Reference: https://www.chegg.com/homework-help/definitions/loop-statement-3<br><br>There are several loops, but we will look at a '''for''' loop using a '''list'''.<br><br># Use a text editor like vi or nano to create the text file called '''for-1.bash'''<br>(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<br>(eg. with vi: press '''ESC''', then type ''':x''' 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:<br><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'''<br>(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<br>(eg. with vi: press '''ESC''', then type ''':x''' 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:<br><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>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><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)'''congratulations message, then you can proceed.<br><br>
= LINUX PRACTICE QUESTIONS =
simulate a quiz:
https://ict.senecacollege.ca/~murray.saul/uli101/uli101_week10_practiceuli101_week11_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:'''
'''Part A: Display Results from Using the sed Utility'''
Note the contents from the following tab-delimited file called '''PART A: WRITE BASH SHELL SCRIPT CODE~murray.saul/uli101/stuff.txt''':(this file pathname exists for checking your work)
# <span style="font-family:courier;font-weight:bold">sed -n '3,6 p'~murray.saul/uli101/stuff.txt</span><br><br># <span style="font-family:courier;font-weight:bold">sed '4 q'Write ~murray.saul/uli101/stuff.txt</span><br><br># <span style="font-family:courier;font-weight:bold">sed '/the expected output from running each of the following Bash shell scripts You can assume that these Bash shell script files have execute permissions/ d' ~murray. Show your worksaul/uli101/stuff.txt</span><br><br># <span style="font-family:courier;font-weight:bold">sed 's/line/NUMBER/g''~murray.saul/uli101/stuff.txt</span>
# Write a Linux sed command to display only lines 5 to 9 for the file:OUTPUT'''~murray.saul/uli101/stuff.txt'''<br><br># Write a Linux sed command to display only lines the begin the pattern “and” for the file:'''~murray.saul/uli101/stuff.txt'''<br><br># Write a Linux sed command to display only lines that end with a digit for the file: '''~murray.saul/uli101/stuff.txt'''<br><br># Write a Linux sed command to save lines that match the pattern “line” (upper or lowercase) for the file: '''~murray.saul/uli101/stuff.txt''' and save results (overwriting previous contents) to: '''~/results.txt'''<br><br>
'''Part C: Writing Linux Commands Using the awk Utility'''
<pre>
</pre>
'''Write the results of each of the following Linux commands for the above-mentioned file:ROUGH WORK:'''
# <span style="font-family:courier;font-weight:bold">awk ‘NR == 3 {print}’ ~murray.saul/uli101/stuff.txt</span><br><br># <span style="font-family:courier;font-weight:bold">awk ‘NR >= 2 && NR <= 5 {print}’ ~murray.saul/uli101/stuff.txt</span><br><br># <span style="font-family:courier;font-weight:bold">awk ‘$1 ~ /This/ {print $2}’ ~murray.saul/uli101/stuff.txt</span><br><br># <span style="font-family:courier;font-weight:bold">awk ‘$1 ~ /This/ {print $3,$2}’ ~murray.saul/uli101/stuff.txt</span><br><br>
# Write a Linux awk command to display all records for the file: '''~/cars''' whose fifth field is greater than 10000.<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><br># Write a Linux awk command to display the second and third fields for the file: '''~/precars''' for records that match the pattern “chevy”.<br><br># Write a Linux awk command to display the first and second fields for all the records contained in the file: '''~/cars'''<br><br>
[[Category:ULI101]]