=INTRODUCTION TO SHELL SCRIPTINGUSING SED & AWK UTILTIES=

:* 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.

|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]

Variables* [https://opensource.com/article/19/8/what| style="padding-are-environment-variables Environment]* [httpsleft://www.linuxtechi.com/variables-in-shell-scripting/#:~:text=User%20Defined%20Variables%3A,like%20a%20real%20computer%20program. User Defined]* [http://osr600doc.xinuos.com/en/SDK_tools/_Positional_Parameters.html#:~:text=A%20positional%20parameter%20is%20a,up%20to%20nine%20positional%20parameters. Positional Parameters]15px;" |'''Commands / Techniques* [http://linuxcommand.org/lc3_man_pages/readh.html read]'''* [https://man7.org/linux/man-pages/man1/readonlysed.1p.html readonlysed]* [https://www.gnuman7.org/softwarelinux/bash/manual/html_node/Commandman-Substitution.html Command Substitution]| style="padding-left:15px;"|Control Flow Statements* [https:pages/man1/enawk.wikipedia1p.org/wiki/Control_flow Purpose]* [https://www.computerhope.com/unix/test.htm test command]* [https://ryanstutorials.net/bash-scripting-tutorial/bash-if-statements.php#:~:text=If%20statements%20(and%2C%20closely%20related,conditions%20that%20we%20may%20set. if statement]* [https://www.tutorialspoint.com/unix/if-else-statement.htm if-else statement]* [https://www.cyberciti.biz/faq/bash-for-loop/#:~:text=A%20'for%20loop'%20is%20a,files%20using%20a%20for%20loop. for loophtml awk]

 |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>

[[Image:shebang.png|thumb|right|200px|The '''shebang line''' <u>must</u> appear on ===Using the '''first line''' and at the '''beginning''' of the shell script.]]Since Linux shells have evolved over a period of time, using a she-bang line '''forces''' the shell script<br>to run in a '''specific shell''', which could prevent errors in case an older shell does not recognize<br>newer features from more recent shells.<br><br>The '''she-bang''' line is a '''special comment''' at top of your shell script to run your shell script<br>in a specific shell.<br><br>'''NOTE:''' The '''shebang line''' <u>must</u> appear on the '''first line''' and at the '''beginning''' of the shell script,<br>otherwise, it will be treated as a regular comment and ignored.<br><br>sed Utility===

To run your shell script by name, you need to assign '''execute permissionsUsage:''' for the user.<br>To run the shell script, you can '''execute''' the shell script using a ''relative'', ''absolute'', or ''relative-to-home'' pathname

''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>

'''Environment Variables''' [[Image:environment.png|thumb|right|500px|Examples of using '''Environment''' and '''User Defined''' variables.]]Shell '''environment variables''' shape the working environment whenever you are logged in Common shell. Some of these variables are displayed via Linux commands * The sed command reads all lines in the diagram displayed on input file and will be exposed to the right-side.expression<br><br>You can issue the pipeline command <span style="font-family:courier;font-weight:bold">set | more</span><br>to view all variables(i.e.<br><br>Placing a dollar sign "<span style="font-family:courier;font-weight:bold">$</span>" prior to the variable name will cause the variable to expand to the value area contained in the variable.  '''User Defined Variables''' <b>User-defined variables</b> are variables that can be used in the shell script for '''customized''' purposes.<br><br>Data can be stored and removed within quotes) one line at a variable using an '''equal sign''' (no spaces on either side of equal sign)time.<br><br>* The '''read''' command expression can be used to prompt the user to enter data into a variable. The '''readonly''' command will prevent<br>the current value of the variable for the remainder of the execution of a shell script.<br><br> '''Positional Parameters and Special Parameters''' [[Image:positional.png|thumb|right|220px|Examples of using '''positional''' and '''special''' parameters.]]A '''positional parameter''' is a variable within a shell program; its value is set from arguments contained in a shell script single quotes or using the '''set''' commanddouble quotes.Positional parameters are numbered * The expression contains an address (match condition) and their values are accessed by using<br>a preceding "'''$'''" an instruction (eg. '''$1''', '''$2''', '''$3''', etc.operation). The positional parameter '''$0''' refers to<br>either * If the '''name of shell''' where command was issued, or '''filename of shell script''' being executed.<br>If using '''positional parameters''' greater than '''9'''line matches the address, then you need to include number within braces.<br><br>Examples: '''echo ${10}''', '''ls ${23}'''<br><br> The '''shift''' command can be used with positional parameters to shift positional parameters<br>to the left by one or more positionsit will perform the instruction. There are a couple of ways to assign values as positional parameters::*Use Lines will display be default unless the '''set–n''' command with the values as argument after the set command:*Run a shell script containing arguments   There are a group of '''special parameters''' that can be option is used for shell scripting.<br>A few of these special parameters and their purpose are displayed below:<br>'''$*''' , '''“$*”''' , '''"$@"''' , '''$#''' , '''$?'''<br><br> === Command Substitution / Math Operations ===to suppress default display

'''Command SubstitutionAddress:'''

[[Image* Can use a line number, to select a specific line (for example:for-command-substitution.png|thumb|right|300px|Example of how a '''for loop with command substitution5''' works.]])<i>* Can specify a range of line numbers (for example: '''Command substitution5,7''' is )* Regular expressions are contained within forward slashes (e.g. /regular-expression/)* Can specify a facility regular expression to select all lines that allows a command<br>to be run and its output to be pasted back on the command line as arguments to another commandmatch a pattern (e.<g '''/i> Reference: https://en^[0-9].wikipedia.org*[0-9]$/wiki/Command_substitution<br><br>''') * If NO address is present, the instruction will apply to ALL lines

<span style="font-family[[Image:courier"><b>command1 $(command2)</b><br>or<br><b>command1 `command2`</b></span><br><br>sed.png|right|500px|]]''Examples'Instruction:''' <span style="font-family:courier;font-weight:bold">file $*'''Action''' to take for matched line(lss)<br>mail -s "message" $(cat email*Refer to table on right-side for list.txt) < message.txtof some<br>echo "The current directory is $(pwd)"<br>echo "The current hostname is $(hostname)"<br>echo "The date is: $(date +'%A %B %d, %Y')"<br>'common instructions''' and their purpose

<pre style="width:30%">num1=5;num2=10echo “$(($num1 + $num2))”15echo “$((num1-num2))”-5((productUsing the awk Utility===num1*num2))echo “$product”50</pre><br>

===Control Flow Statements===<br> <table align="right"><tr valign="top"><td>[[Image:test-1.png|thumb|right|140px|Examples of simple comparisons using the test command.]]</td><td>[[Image:test-2.png|thumb|right|140px|Examples of using additional comparisons using the test command.]]</td></table>'''Control Flow Statements''' are used to make your shell scripts<br>more '''flexible''' and can '''adapt''' to changing situations.<br><br>In order to use control flow statements, you need to test a condition to get<br>'''TRUE''' (zero value) or '''FALSE''' (non zero value). This can be done two ways:<ul><li>Run a command to get the exit status (<span style="font-family:courier;font-weightUsage:bold;">$?</span>)</li><li>Use the '''test''' command</li></ul><br>Refer to the diagrams on the right to see how to use the test command.<br><br>

You CANNOT use the <span style="font-familycolor:courierblue;font-weight:bold;">&lt;</span> or <span style="font-family:courier;font-weight:bold;">&gt;awk [-F] 'selection-criteria {action}’ file-name</span> symbols when using the test command since these are redirection symbols. Instead, you need to use '''options''' when performing numerical comparisons.Refer to the diagrams to the right '''test options''' and their purposes.<br><br>

A '''logic statement''' is used to determine which Linux commands<br>are executed basedon the result of a conditionHow It Works:<br>'''TRUE''' (zero value) or '''FALSE''' (non-zero value).

[[Image:logic-1* The '''awk''' command reads all lines in the input file and will be exposed to the expression (contained within quotes) for processing.*The '''expression''' (contained in quotes) represents '''selection criteria''', and '''action''' to execute contained within braces '''{}'''* if selection criteria is matched, then action (between braces) is executed.png|thumb|right|210px|Example of using * The '''–F''' option can be used to specify the default '''field delimiter''' (separator) character<br>eg. '''ifawk –F”;”''' logic control (would indicate a semi-flow statementcolon delimited input file).]]

There are several logic statements, but we will just concentrate on the if statement.<pre style="width:20%">if test condition then command(s) fi</pre> Refer to the diagram to the right for using the '''if logic statementSelection Criteria''' with the '''test''' command.

<br* You can use a regular expression, enclosed within slashes, as a pattern. For example: '''/pattern/'''* The ~ operator tests whether a field or variable matches a regular expression. For example: '''$1 ~ /^[0-9]/'''* The '''!~''' operator tests for no match. For example: '''$2 !~ /line/'''* You can perform both numeric and string comparisons using relational operators ( '''><br''' , '''>=''' , '''<br>''' , '''<br>=''' , '''==''' , '''!=''' ).* You can combine any of the patterns using the Boolean operators '''||''' (OR) and '''&&''' (AND).* You can use built-in variables (like NR or "record number" representing line number) with comparison operators.<br>For example: '''if-else statement:NR >=1 && NR <= 5'''

[[Image:logic-2.png|thumb|right|210px|Example of how an '''if-else''' control-flow statement.]] Unlike using an ''if'' statement, an '''if-else''' statement take '''two different sets of actionsAction (execution):'''<br>based on the results of the test condition.<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).

<pre style="widthINVESTIGATION 1:20%">if test condition then command(s) else command(s) fi</pre>USING THE SED UTILITY=

'''Loop Statements'''[[Image:loop-1.png|thumb|right|210px|Example of using the '''for''' looping control-flow statement.]]''A <b>loop statement</b> is a series of steps or sequence of statements executed repeatedly<br>zero or more times satisfying the given condition is satisfied.''<br>Reference: https://www.chegg.com/homework-help/definitions/loop-statement-3 There are several loops, but we will look at the '''for loop''' using a '''list'''. <pre style="width:20%">for item in list do command(s) done</pre> Refer to the diagram above and to the extreme right side for an example using the '''for loop''' with a '''list'''.<br><br> =INVESTIGATION 1: CREATING A SHELL SCRIPT= <br>In this sectioninvestigation, you will learn how to create and run a manipulate text using the '''Bash Shell scriptsed'''utility.

# '''Login''' to your matrix accountand confirm you are located in your '''home''' directory.<br><br># Issue a Linux command to create a directory called '''confirmsed''' 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 namechecking-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 '''address'Environment variables'' make your shell script adaptable by ALL users.to display lines using the sed utility<br><br>(eg. ''line # '', '''Saveline #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 's simply run it by its filename1 p' data. 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|An Using the sed command to display a '''error messagerange''' 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 | 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 '''s''' 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.txt | tee sed-5./hellotxt</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 messageregular 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><br>[[Image:sed-5. One major cause is 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 output for the correct Bash shell scriptfollowing Linux pipeline command:<br><span style="color:blue;font-weight:bold;font-family:courier;">who | sed -n '/^[a-m]/ p' | tee sed-8. This requires that txt | more</span><br><br>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: SHE-BANG LINE / VARIABLES / PARAMETERS= In this sectionthe next investigation, you will add a '''she-bang''' line at the top of your shell script to force the shell script to run in a specified shell when executed. You will also learn how to use '''variables''', '''positionalmanipulate text using the ''' and awk'''special parameters''' to make your shell scripts more adaptableutility.<br><br>

# 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 understand why a ''she-bang'awk''' line should be useddirectory.<br><br># Use Let's download a text editor to '''edit''' the '''hello''' shell script database file that you created in the <u>previous</u> investigationcontains information regarding classic cars.<br><br># Add Issue the following line to the <u>bottom</u> of the file (''linux command ('''copy''' and '''paste''' to prevent ''errors''save time):<br><span style="font-familycolor:courierblue;font-weight:bold;">echo "The current shell you are using isfont-family: $(ps -o cmd= -p $$|cut -d' ' -f1)courier;"</span><br>wget <brnowiki>'''FYIhttps:''' This command displays //ict.senecacollege.ca/~murray.saul/uli101/cars.txt</nowiki></span><br><br># Issue the '''namecat''' command to quickly view the contents of the ''shell'cars.txt' that the shell script is running in'' file.<br><br>The "'''print'''" action (command within ) is the <u>default<span style="font-family:courier;font-weight:bold;"/u>$( )action of awk to print</spanbr> uses all selected lines that match a technique known as '''command substitutionpattern'''.<br><br># Issue the following Linux command to change to the This '''action''' (contained in braces) can provide more options<br>such as printing '''Bourne Shellspecific fields''':of selected lines (or records) from a database.<br><span style="colorbr>[[Image:blue;fontawk-weight:bold;font-family:courier;">sh</span><br><br>You should notice your shell prompt changed that indicates that you are in a different shell1.png|thumb|right|400px|Using the awk command to display matches of the pattern '''ford'''.<br><br>[[Image:hello2]]# Issue the following linux command all to display all lines (i.e.png|thumb|right|275px|Changing records) in the Bourne shell and running shell script '''withoutcars.txt''' a '''She-bang'database that matches the pattern (or "make") called '' 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 '/helloford/ {print}' cars.txt</span><br><br>You should see that you are currently running the shell script "We will use '''shpipeline commands'''"<br>which represents to both display stdout to the '''Bourne shell'''.screen and save to files for <bru>confirmation<br/u>of running these pipeline commands when run a '''NOTE:checking-script''' Due to the fact that shells (and their features) have '''evolved''' over a period of time,later in this investigation.<br>an error may occur if you include a <br># Issue the following linux pipeline command all to display records<br>in the '''NEWER shell featurecars.txt''' database that contain the pattern (i.e.g. ''Bash Shell''make) but run it in an '''OLDER shellford''' (For example: the ''Bourne Shell'').<<br><br>[[Imagespan style="color:sheblue;font-bangweight:bold;font-1.png|thumb|right|275px|Adding a family:courier;">awk '/ford/''shecars.txt | tee awk-bang line''' 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).]]1.txt</span><br><br>What do you notice? You can add a '''special commentshould notice ALL lines displayed <u>without</u> using ''' called a search criteria'''she-bang line''' at the BEGINNING of the .<ubr>FIRST line</ubr> of your shell script to You can use ''builtin''force''' it to run in variables''' with the shell you want (for example: the Bash shell).<br><br> # Edit your '''helloprint''' shell script using a text editorcommand for further processing.<br><brWe will discuss the following variables in this tutorial:<br># <br>[[Image:awk-2.png|thumb|right|400px|Using the awk command to print search results by '''Insertfield number''' the following line at the .]]'''beginning$0''' of the - Current record (entire line)<br>'''first$1''' line of your hello file:- First field in record<br>'''$n''' - nth field in record<span style="fontbr>'''NR''' -family:courier;font-weight:bold;">#!/bin/bashRecord Number (order in database)</spanbr><br><br>This is referred to as a '''she-bang lineNF'''. It forces this script to be run - Number of fields in the '''Bash Shell'''.current record<br>When your Bash Shell script finishes execution<br>For a listing of more variables, you are returned to please consult your current shell that you are using (which in our case in Matrix, is still the Bash shell)course notes.<br><br>[[Image:hello3.png|thumb|right|275px|Changing # Issue the following linux pipeline command to display the Bourne shell and running shell script '''withmodel''' a , '''She-bangyear''' line (forcing script to run in the , '''Bashquantity''' shell).]]# and price<br>in the '''Savecars.txt''' your editing changes and database for makes of '''exitchevy''' your text editor.<br><br># While in the Bourne shell, issue the following Linux command:<br><span style="color:blue;font-weight:bold;font-family:courier;">.awk '/hello<chevy/span><br{print $2,$3,$4,$5}' cars.txt | tee awk-2.txt</span><br><br>You should notice Notice that the shell name is running in the a '''Bash shellspace'''.<is the delimiter for the fields that appear as standard output.<br><br> # It is a good idea to rename your shell script to include an The '''extensiontilde character''' to<br>explain that this is '''Bash Shell script~''' file (referred is used to as search for a "''portable Bash shell script''")pattern or display standard output for a particular field. <br><br># Issue the following Linux linux pipeline command to rename your shell script file:display all '''plymouths''' ('''plym''')<br>by '''model name''', '''price''' and '''quantity''':<br><span style="color:blue;font-weight:bold;font-family:courier;">mv hello hello.bash<awk '$1 ~ /plym/span>{print $2,$3,$4,$5}' cars.txt | tee awk-3.txt<br/span><br># Confirm that the modification work by running your Bash shell script:<br><span style="color:blue;font-weight:bold;font-family:courier;"You can also use '''comparison operators''' to specify conditions for processing with matched patterns<br>when using the awk command./hello.bashSince they are used WITHIN the awk expression,</spanbr>they are not confused with redirection symbols<br><br># Enter [[Image:awk-3.png|thumb|right|400px|Using the following Linux awk command to display results based on '''exitcomparison operators''' the .]]''Bourne shell'<' and return to your ''Bash shell'': &nbsp;&nbsp;&nbsp;&nbsp;Less than<br>'''<span style="color:blue''' &nbsp;font-weight:bold&nbsp;font-family:courier;"Less than or equal<br>exit</span'''>''' &nbsp;&nbsp;&nbsp;&nbsp;Greater than<br><br>Let's use some ''>='ENVIRONMENT variables''' in our Bash Shell script.&nbsp;&nbsp;Greater than or equal<br>'''==''' &nbsp;&nbsp;Equal<br># Use a text editor to edit the shell script called '''hello.bash!='''&nbsp;&nbsp;&nbsp;Not equal<br><br># Add Issue the following lines linux pipeline command to display display the <u>bottom</u> of the ''hello.bash'car make''', '''model''', '''quantity''' file:<br><span style="font-familyand '''price''' of all vehicles whose '''prices are less than $5,000''':<br><span style="color:courierblue;font-weight:bold;">echo<br>echo "The current directory location isfont-family: $PWDcourier;"<br>echo "The current user home directory is: awk '$HOME"5 <br>echo</span5000 {print $1,$2,$4,$5}' cars.txt | tee awk-4.txt</span><br><br># Save your editing changes and exit your text editor.What do you notice?<br><br>[[Image:hello4-0.png|thumb|right|330px|Running # Issue the following linux pipeline command to display display '''price''',<u>modified</ubr> ''hello.bash'quantity''', '''model''' and '''car make''' of vehicles whose '''prices are less than $5,000''' Bash shell script by using relative pathname: <br><span style="color:blue;font-weight:bold;font-family:courier;">awk '$5 < 5000 {print $5,$4,$2,$1}'cars./hellotxt | tee awk-5.bash''txt</span>]]<br><br># To confirm that you properly renamed your shell script,<br>run Issue the following shell script:linux pipeline command to display the '''car make''',<br><span style="color'''year''' and '''quantity''' of cars that '''begin''' with the '''letter 'f'''':blue;font<br><span style="color:blue;font-weight:bold;font-family:courier;">awk '$1 ~ /^f/ {print $1,$2,$4}' cars./hellotxt | tee awk-6.bashtxt</span><br><br>Take time to view the output and the values of the environment variables[[Image:awk-4.<br><br># Issue png|thumb|right|400px|Using the following Linux awk command to add your current directory to the display combined search results based on '''PATHcompound operators''' environment variable.]]Combined pattern searches can be made<br>by using '''compound operator''' symbols:<br><span style="color:bluebr>'''&&''' &nbsp;&nbsp;&nbsp;font-weight:bold&nbsp;font-family:courier;">PATH=$PATH:.</span>(and)<br>'''||''' &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(or)<br>[[Image:hello4.png|thumb|right|330px|Running <ubr>modified</ubr> # Issue the following linux pipeline command to list all ''hello.bash'fords''' Bash shell script by entering <u>just</ubr> whose '''filenameprice is greater than $10,000''' (i.e. :<br><span style="color:blue;font-weight:bold;font-family:courier;">awk ''hello.bash''<$1 ~ /ford/span> and NOT <span style="font-family:courier;"&& $5 >10000 {print $0}''cars./hellotxt | tee awk-7.bash''txt</span> shown in previous diagram).]]<br><br># Issue the following Linux linux command to confirm that the current directory ('''"."copy and paste''' has been added to the '''PATH''' environment variablesave time):<br><span style="color:blue;font-weight:bold;font-family:courier;">echo $PATHwget <nowiki>https://ict.senecacollege.ca/~murray.saul/uli101/cars2.txt</nowiki></span><br><br># Issue the following '''cat''' command to run your Bash shell script just by name:quickly view the contents of the '''cars2.txt''' file.<br><span style="color:blue;font-weight:bold;font-family:courier;">hello.bash</spanbr># Issue the following linux pipeline command to display the '''year'''<br><br>Did your Bash shell script run?<br><br># Exit your Matrix session, and log back into your Matrix session.<br><br># Re-run '''quantity''' of cars that '''begin''' with the '''hello.bashletter 'f'''' shell script by just using the name.<br><br>What did you notice?<br><br>The setting of for the '''PATHcars2.txt''' environment variable only worked in the current session only.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$4}' cars2.txt | tee awk-8.<br>You will in a <u>futuretxt</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>

:In the next investigationThe purpose of this section is to obtain '''extra practice''' to help with '''quizzes''', you will learn to use your '''command substitutionmidterm''' , and your '''math operationsfinal exam''' in your shell scripts.<br>

=INVESTIGATION 3Here is a link to the MS Word Document of ALL of the questions displayed below but with extra room to answer on the document tosimulate a quiz: COMMAND SUBSTITUTION / MATH OPERATIONS=<br>In this section, you will learn how to use '''command substitution''' and '''math operations''' in your shell scripts.

''For example'Review Questions:'''

<span style="font-family'''Part A:courier;font-weight:bold;">echo "The current date and time is: $(date)"</span>Display Results from Using the sed Utility'''

Let's create a Bash shell script that uses command substitution that displays<brpre>'''text''' Line one.This is the second line.This is the third.This is line four.Five.Line six followsFollowed by 7Now line 8and values of '''environment variables''' in a series of <span style="font-family:courier;font-weight:bold;">echoline nineFinally, line 10</span> statements.<br><brpre>

# Confirm that you are located in your '''home''' directory in your Matrix account.<br><br># Use a text editor to create a Bash shell script called '''command-substitution.bash'''<br><br># Add the following lines to Write the beginning results of this file:<br><span style="font-family:courier;font-weight:bold;">#!/bin/bash<br>echo<br>echo "MY ACCOUNT INFORMATION:"<br>echo<br>echo "Username: $(whoami)"<br>echo<br>echo "Current Directory: $(pwd)"<br>echo<br></span><br>[[Image:commandsubstitution1.png|thumb|right|275px|Output each of a shell script using command substitution.]]# Save your editing changes and exit your text editor.<br><br># Issue the '''chmod''' command to add execute permissions<br>following Linux commands for the '''commandabove-substitution.bash''' mentioned file.<br><br># Issue the following to run the user-variables.bash Bash shell script:<br><span style="color:blue;font-weight:bold;font-family:courier;">./command-substitution.bash</span><br><br>Confirm that your shell script displays the correct information for your Matrix account.<br><br>

Since you do NOT have to declare the '''data# <span style="font-family:courier;font-weight:bold">sed -typen '3,6 p'' of a variable (as opposed to compiled program such as the C-programming language),~murray.saul/uli101/stuff.txt</span><br><br> numbers would be stored as # <span style="font-family:courier;font-weight:bold">sed '4 q''text''' in variables~murray.saul/uli101/stuff. Therefore, it is important to use the construct txt</span><br><br># <span style="color:blue;font-family:courier;font-weight:bold">(( ))sed '/the/ d' ~murray.saul/uli101/stuff.txt</span> to <ubr>convert</ubr># <span style="font-family:courier;font-weight:bold"> numbers (stored as ''text'') into '''numbers'sed 's/line/NUMBER/g'~murray.saul/uli101/stuff.txt</span>

'''Perform Part B: Writing Linux Commands Using the Following Steps:sed Utility'''

# Confirm that you are located in your '''home''' directory in your Matrix account.<br><br># To demonstrate the need for the '''( )''' construct, issue the following Write a single Linux command from the shell:<br><span style="color:blue;font-family:courier;font-weight:bold">echo "1 + 2"</span><br><br>What did you notice?<br><br># Issue the following Linux commands (using the ''math construct''):<br><span style="color:blue;font-family:courier;font-weight:bold">echo "$((1 + 2))"</span><br><br>What did you notice?<br>The <span style="font-family:courier;font-weight:bold">(( ))</span> construct converted values '''1''' and '''2''' from ''text'' to '''binary numbers'''.<br>The '''$''' in front of the construct '''expands''' the result of the calculation.<br><br># Issue the following Linux commands demonstrating other types of math calculations:<br><span style="color:blue;font-family:courier;font-weight:bold">echo "$((2 - 3))"</span><br><span style="color:blue;font-family:courier;font-weight:bold">echo "$((2 * 3))"</span><br><span style="color:blue;font-family:courier;font-weight:bold">echo "$((2 / 3))"</span><br><span style="color:blue;font-family:courier;font-weight:bold">echo "$((2 ** 3))"</span><br><br>'''NOTE:''' You may notice that '''dividing''' '''2''' by '''3''' shows a '''zero''' result. To perform decimal calculations would require<br>the use the '''awk''' or '''bc''' Linux commands (we will '''NOT''' cover that method to work with ''decimal numbers'' in this course).<br><br>You can use the ''math construct'' with variables as well.<br><br># Issue the following Linux commands demonstrating using the ''math construct'' with '''variables''':<br><span style="color:blue;font-family:courier;font-weight:bold">num1=34</span><br><span style="color:blue;font-family:courier;font-weight:bold">num2=12</span><br><span style="color:blue;font-family:courier;font-weight:bold">echo "$((num1 * num2))"</span><br><br>What did you notice?<br><br>You can create variables and assign them values in the ''math construct'' as well.<br><br># Issue the following Linux commands demonstrating using the math construct with '''variables''':<br><span style="color:blue;font-family:courier;font-weight:bold">num1=5</span><br><span style="color:blue;font-family:courier;font-weight:bold">num2=3</span><br><span style="color:blue;font-family:courier;font-weight:bold">((result = num1 ** num2))</span><br><span style="color:blue;font-family:courier;font-weight:bold">echo "The result is: $result"</span><br><br># Use a text editor to create a Bash shell script called '''dog-years.bash'''<br><br># Add the following lines to the beginning specified tasks for each of this file:<br><span style="font-family:courier;font-weight:bold;">#!/bin/bash<br>echo<br>dogFactor=7<br>read -p "Please enter your age (in years): " humanYears<br>((dogYears = humanYears * dogFactor))<br>echo "You age in dog-years is: $dogYears"<br>echo<br></span><br># Save your editing changes and exit your text editor.<br><br>[[Image:mathops1.png|thumb|right|275px|Output of a shell script with math operations using the '''math construct'''.]]# Issue the '''chmod''' command to add execute permissions<br>for the user for the '''dog-years.bash''' file.<br><br># Issue the following to run the user-variables.bash Bash shell script:<br><span style="color:blue;font-weight:bold;font-family:courier;">./dog-years.bash</span><br><br>Enter <u>your</u> age to see what happens.<br><br># Issue the following to run a checking script:<br><span style="color:blue;font-weight:bold;font-family:courier;">bash /home/murray.saul/myscripts/week10-check-3 | 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 proceedquestions.<br><br>

=INVESTIGATION 4# Write a Linux sed command to display only lines 5 to 9 for the file: CONTROL FLOW STATEMENTS ='''~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>In this section, you will learn how # Write a Linux sed command to use control-flow statementsdisplay only lines that end with a digit for the file: '''~murray.saul/uli101/stuff.txt'''<br><br># Write a Linux sed command to make your shell script save lines that match the pattern “line” (upper or lowercase) for the file: '''behave differently~murray.saul/uli101/stuff.txt''' under and save results (overwriting previous contents) to: '''different situations or conditions~/results.txt'''.<br><br>

'''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 '''&lt;''' and '''&gt;''' 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''' (&lt;), '''-le''' (&lt;&#61;), '''-gt''' (&gt;), '''-ge''' (&gt;&#61;;), '''-eq''' (&#61;), '''-ne''' (!&#61;)<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 '''&#91; &#93;''' 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;">&#91;$number1 -gt $number2&#93;</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;">&#91; $number1 -gt $number2 &#93;</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>&nbsp;&nbsp;&nbsp;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>&nbsp;&nbsp;&nbsp;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>&nbsp;&nbsp;&nbsp;echo "The first number is greater than the second number."<br>else<br>&nbsp;&nbsp;&nbsp;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>&nbsp;&nbsp;&nbsp;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>&nbsp;&nbsp;&nbsp;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>

= LINUX PRACTICE QUESTIONS = The purpose of this section is to obtain '''extra practice''' to help with '''quizzes''', your '''midterm''', and your '''final examNote the contents from the following tab-delimited file called '''. Here is a link to the MS Word Document of ALL of the questions displayed below but with extra room to answer on the document tosimulate a quiz: https://ict.senecacollege.ca/~murray.saul/uli101/uli101_week10_practicestuff.docxtxt''':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, etcthis file pathname exists for checking your work).

'''Write the answer to each question below the question in the space provided# <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 Bash shell script that clears the screen and displays the text Hello World on the screen.<br><br>What permissions are required to run this Bash shell script?<br><br>What are the different ways that you can run this Bash shell script from the command line?<br><br># Write a Bash shell script that clears the screen, prompts the user for their '''full name''' and then prompts Part D: Writing Linux Commands Using the user for their awk Utility'''age''',<br>then clears the screen again and welcomes the user by their name and tells them their age.<br><br>What comments would you add to the above script’s contents to properly document this Bash shell script to be understood<br>for those users that would read / edit this Bash shell script’s contents?<br><br># Write a Bash shell script that will first set the value of a variable called '''number''' to '''23''' and make this variable '''read-only'''.<br>Then the script will clear the screen and prompt the user to enter a value for that variable called number to another value.<br>Have the script display the value of the variable called number to prove that it is a read-only variable.<br><br>When you ran this Bash shell script, did you encounter an error message?<br>How would you run this Bash shell script, so the error message was NOT displayed?<br><br># Write a Bash shell script that will clear the screen and then display all arguments that were entered after your Bash shell script when it was run. Also have the Bash shell script display the number of arguments that were entered after your Bash shell script.<br><br><br>

'''Write a single Linux command to perform the expected output from running specified tasks for each of the following Bash shell scripts You can assume that these Bash shell script files have execute permissionsquestions. Show your work.'''

# 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>