Difference between revisions of "Tutorial10: Shell Scripting - Part 1"

From CDOT Wiki
Jump to: navigation, search
(INVESTIGATION 2: USING VARIABLES IN SHELL SCRIPTS)
 
(492 intermediate revisions by the same user not shown)
Line 1: Line 1:
=INTRODUCTION TO SHELL SCRIPTING=
+
=USING SED & AWK UTILTIES=
 
<br>
 
<br>
 
===Main Objectives of this Practice Tutorial===
 
===Main Objectives of this Practice Tutorial===
  
:* Explain the purpose of the '''she-bang line''' contained at the top of a shell script.
+
:* Use the '''sed''' command to '''manipulate text''' contained in a file.
  
:* List rules for naming a Bash script file.
+
:* List and explain several '''addresses''' and '''instructions''' associated with the '''sed''' command.
  
:* Explain how to set '''permissions''' and how to '''execute''' a shell script.  
+
:* Use the '''sed''' command as a '''filter''' with Linux pipeline commands.
  
:* Explain the purpose of '''environment''' and '''user-defined''' variables.
+
:* Use the '''awk''' command to '''manipulate text''' contained in a file.
  
:* Explain the purpose of '''control flow statements'''.
+
:* List and explain '''comparison operators''', '''variables''' and '''actions''' associated with the '''awk''' command.
  
:* Explain the purpose of the '''test''' command.
+
:* Use the '''awk''' command as a '''filter''' with Linux pipeline commands.
 
+
<br><br>
:* Explain the purpose and usage of the '''if''' logic statement and the '''for''' loop statement
 
  
 
===Tutorial Reference Material===
 
===Tutorial Reference Material===
Line 31: Line 30:
 
|- valign="top" style="padding-left:15px;"
 
|- valign="top" style="padding-left:15px;"
  
|colspan="2" |Course Notes:<ul><li>[https://ict.senecacollege.ca/~murray.saul/uli101/ULI101-Week10.pdf PDF] | [https://ict.senecacollege.ca/~murray.saul/uli101/ULI101-Week10.pptx PPTX]</li></ul>
+
|colspan="2" |'''Slides''':<ul><li>Week 11 Lecture 1 Notes:<br> [[Media:ULI101-Week11.1.pdf | PDF]] | [https://matrix.senecacollege.ca/~chris.johnson/ULI101/ULI101-Week11.1.pptx PPTX]</li><li>Week 11 Lecture 2 Notes:<br> [[Media:ULI101-Week11.2.pdf | PDF]] | [https://matrix.senecacollege.ca/~jason.carman/slides/ULI101-Week11.2.pptx PPTX] <br></li></ul>
  
  
|  style="padding-left:15px;" |Shell Scripting
+
|  style="padding-left:15px;" |'''Text Manipulation:'''
* [https://searchdatacenter.techtarget.com/definition/shell-script Purpose]
+
* [https://www.digitalocean.com/community/tutorials/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-linux Purpose of using the awk utility]
  
Variables
+
|  style="padding-left:15px;" |'''Commands:'''
* [https://opensource.com/article/19/8/what-are-environment-variables Environment]
+
* [https://man7.org/linux/man-pages/man1/sed.1p.html sed]
* [https://www.linuxtechi.com/variables-in-shell-scripting/#:~:text=User%20Defined%20Variables%3A,like%20a%20real%20computer%20program. User Defined]
+
* [https://man7.org/linux/man-pages/man1/awk.1p.html awk]
Commands
 
* [http://linuxcommand.org/lc3_man_pages/readh.html read]
 
* [https://man7.org/linux/man-pages/man1/readonly.1p.html readonly]
 
  
|  style="padding-left:15px;"|Control Flow Statements
 
* [https://en.wikipedia.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.cyberciti.biz/faq/bash-for-loop/#:~:text=A%20'for%20loop'%20is%20a,files%20using%20a%20for%20loop. for loop]
 
  
|colspan="1" style="padding-left:15px;" width="30%"|Instructional Videos:<ul><li>[https://www.youtube.com/watch?v=kxEP-KUhOSg&list=PLU1b1f-2Oe90TuYfifnWulINjMv_Wr16N&index=5 Bash Shell Scripting - Part 1]</li><li>[https://www.youtube.com/watch?v=cQepf9fY6cE Creating and Running a Shell Script]</li></ul>
+
|colspan="1" style="padding-left:15px;" width="30%"|'''Brauer Instructional Videos:'''<ul><li>[https://www.youtube.com/watch?v=npU6S61AIko&list=PLU1b1f-2Oe90TuYfifnWulINjMv_Wr16N&index=14 Using the sed Utility]</li><li>[https://www.youtube.com/watch?v=OV3XzjDYgJo&list=PLU1b1f-2Oe90TuYfifnWulINjMv_Wr16N&index=13 Using the awk Utility]</ul>
 
|}
 
|}
  
 
= KEY CONCEPTS =
 
= KEY CONCEPTS =
  
''A shell script is a computer program designed to be run by the Unix shell, a command-line interpreter.<br> The various dialects of shell scripts are considered to be scripting languages.''
 
  
Reference:  https://en.wikipedia.org/wiki/Shell_script
+
===Using the sed Utility===
  
===Creating & Executing Shell Scripts===
 
  
[[Image:ipso.png|thumb|right|500px|An '''IPSO Diagram''' (INPUT, PROCESSING, STORAGE, OUTPUT) can be used to map-out and then list the sequence of steps to assist when coding your shell script.]]
+
'''Usage:'''
It is recommended to '''plan''' out on a piece of paper the purpose of the shell script.<br>You can do this by creating a simple '''IPSO''' diagram (stands for '''INPUT''', '''PROCESSING''', '''STORAGE''', '''OUTPUT''').
 
  
First, list the INPUTS into the script (eg. prompting user for data, reading data from file, etc), then listing the expected OUTPUTS from the script. You can then list the steps to process the INPUT to provide the OUTPUT (including file storage).
+
'''<span style="color:blue;font-weight:bold;font-family:courier;">Syntax:  sed [-n] 'address instruction' filename</span>'''
  
Once you have planned your shell script by listing the sequence of steps (i.e. PROCESSING) in your script, you need to create a file (using a '''text editor''') that will contain your Linux commands.<br><br>'''NOTE:'''  Avoid using filenames of already existing Linux Commands to avoid confusion.<br>Using shell script filenames that include the file extension of the shell that the script will run within is recommended.
 
  
'''Using a Shebang Line'''
+
'''How it Works:'''
  
[[Image:shebang.png|thumb|right|200px|The '''shebang line''' <u>must</u> appear on the '''first line''' and at the '''beginning''' of the shell script.]]If you are learning Bash scripting by reading other people’s code you might have noticed<br>that the first line in the scripts starts with the <span style="font-family:courier;font-weight:bold">#!</span> characters and the path to the Bash interpreter.
+
* The sed command reads all lines in the input file and will be exposed to the expression<br>(i.e. area contained within quotes) one line at a time.
 
+
* The expression can be within single quotes or double quotes.
<i>This sequence of characters (#!) is called '''shebang''' and is used to tell the operating system<br>which interpreter to use to parse the rest of the file. </i>Reference: https://linuxize.com/post/bash-shebang/
+
* The expression contains an address (match condition) and an instruction (operation).
 
+
* If the line matches the address, then it will perform the instruction.
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.
+
* Lines will display be default unless the '''–n''' option is used to suppress default display
 
+
<br>
'''Setting Permissions &amp; Running a Shell Script'''
+
'''Address:'''
 
 
To run your shell script by name, you need to assign '''execute permissions''' for the user.<br>To run the shell script, you can '''execute''' the shell script using a ''relative'', ''absolute'', or ''relative-to-home'' pathname
 
 
 
'''Example:<br><br><span style="font-family:courier;">chmod u+x myscript.bash<br>./myscript.bash<br>/home/username/myscript.bash<br>~/myscript.bash</span>
 
'''
 
 
 
===Using Variables in Shell Scripts===
 
 
 
'''Definition'''
 
 
 
''<b>Variables</b> are used to '''store information''' to be referenced and manipulated in a computer program.<br>They also provide a way of labeling data with a descriptive name, so our programs can be understood<br>more clearly by the reader and ourselves.''<br>Reference: https://launchschool.com/books/ruby/read/variables
 
 
 
 
 
'''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 in the diagram displayed on the right-side.<br>(you can issue the pipeline command '''set | more''' to view all variables)
 
 
 
Placing a dollar sign ('''$''') prior to the variable name will cause the variable to expand to the value contained in the variable.
 
  
 +
* Can use a line number, to select a specific line (for example: '''5''')
 +
* Can specify a range of line numbers (for example: '''5,7''')
 +
* Regular expressions are contained within forward slashes (e.g. /regular-expression/)
 +
* Can specify a regular expression to select all lines that match a pattern  (e.g '''/^[0-9].*[0-9]$/''')
 +
* If NO address is present, the instruction will apply to ALL lines
  
'''User Defined Variables'''
 
  
''<b>User-defined variables</b> are variables which can be '''created by the user''' and exist in the session. This means that no one can access user-defined variables that have been set by another user,<br>and when the session is closed these variables expire.''<br>Reference: https://mariadb.com/kb/en/user-defined-variables/
+
[[Image:sed.png|right|500px|]]
<br><br>
+
'''Instruction:'''
Data can be stored and removed within a variable using an '''equal sign'''.<br>The '''read''' command can be used to prompt the user to enter data into a variable.<br>Refer to the diagram on the right-side to see how user-defined variables are assigned data.
+
*'''Action''' to take for matched line(s)
 +
*Refer to table on right-side for list of some<br>'''common instructions''' and their purpose
 
<br><br>
 
<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 an argument specified on the command line that invokes the program.
+
===Using the awk Utility===
Positional parameters are numbered and their values are accessed by using a preceding "'''$'''" (eg. '''$1''', '''$2''', '''$3''', etc.). The positional parameter '''$0''' refers to either the name of shell where command was issued, or name of shell script being executed. If using '''positional parameters''' greater than '''9''', then you need to include number within braces.<br>Examples: '''echo ${10}''', '''ls ${23}'''
 
 
 
The '''shift''' command can be used with positional parameters to shift positional parameters<br>to the left by one or more positions.
 
 
 
There are a couple of ways to assign values as positional parameters:
 
:*Use the '''set''' 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 used for shell scripting.<br>A few of these special parameters and their purpose are displayed below:<br>'''$*''' , '''“$*”''' , '''"$@"''' , '''$#''' , '''$?'''
 
 
 
Refer to the diagram to the right for examples using positional and special parameters.
 
 
 
===Using Control Flow Statements in Shell Scripts===
 
 
   
 
   
<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 more '''flexible''' and can '''adapt''' to changing situations.
 
  
The special parameter '''$?''' Is used to determine the '''exit status''' of the previously issued Linux command.
+
'''Usage:'''
The exit status will either display a '''zero''' (representing TRUE) or a '''non-zero''' number (representing FALSE). The test command can be used with control flow statements to control the sequence of a shell script.
 
  
You CANNOT use the '''>''' or '''<''' symbols when using the test command since these are redirection symbols. Instead, you need to use options when performing numerical comparisons.
+
<span style="color:blue;font-weight:bold;font-family:courier;">awk [-F] 'selection-criteria {action}’ file-name</span>
Refer to the table below for test options and their purposes.
 
  
There are <u>other</u> comparison options that can be used with the test command such as testing to see if a regular file or directory pathname exists, or if the regular file pathname is –non-empty.
 
  
Refer to diagrams to the right involving some of the options used with the '''test''' command. Refer to the test man pages for a full list of options for the test command.
+
'''How It Works:'''
  
'''Logic Statements'''
+
* 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.
 +
* The '''–F''' option can be used to specify the default '''field delimiter''' (separator) character<br>eg. '''awk –F”;”'''  (would indicate a semi-colon delimited input file).
 +
<br>
 +
'''Selection Criteria'''
  
A '''logic statement''' is used to determine which Linux commands to be executed based<br>on the result of a condition (i.e. TRUE (zero value) or FALSE (non-zero value)).
+
* 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 ( '''>''' , '''>=''' , '''<''' , '''<=''' , '''==''' , '''!=''' ).
 +
* 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: '''NR >=1 && NR <= 5'''
 +
<br>
 +
'''Action (execution):'''
  
<table align="right"><tr valign="top"><td>[[Image:logic-1.png|thumb|right|250px|Example of using the '''if''' logic control-flow statement.]]</td><td>[[Image:loop-1.png|thumb|right|250px|Example of using the '''for''' looping control-flow statement.]]</td></table>
+
* Action to be executed is contained within braces '''{}'''
 +
* 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).
  
There are several logic statements, but we will just concentrate on the if statement.
+
=INVESTIGATION 1: USING THE SED UTILITY=
<pre style="width:20%">
 
if test condition
 
  then
 
    command(s)
 
fi
 
</pre>
 
  
Refer to the diagram immediately to the right for using the '''if logic statement''' with the '''test''' command.
+
<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>
  
'''Loop Statements'''
+
In this investigation, you will learn how to manipulate text using the '''sed''' utility.
  
''A <b>loop statement</b> is a series of steps or sequence of statements executed repeatedly 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'''.
+
'''Perform the Following Steps:'''
 
 
<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'''.
+
# '''Login''' to your matrix account and confirm you are located in your '''home''' directory.<br><br>
 +
# Issue a Linux command to create a directory called '''sed'''<br><br>
 +
# Issue a Linux command to <u>change</u> to the '''sed''' directory and confirm that you are located in the '''sed''' directory.<br><br>
 +
# Issue the following Linux command to download the data.txt file<br>('''copy and paste''' to save time):<br><span style="color:blue;font-weight:bold;font-family:courier;">wget <nowiki>https://ict.senecacollege.ca/~murray.saul/uli101/data.txt</nowiki></span><br><br>
 +
# Issue the '''more''' command to quickly view the contents of the '''data.txt''' file.<br>When finished, exit the more command by pressing the letter <span style="color:blue;font-weight:bold;font-family:courier;">q</span>[[Image:sed-1.png|thumb|right|300px|Issuing the '''p''' instruction without using the '''-n''' option (to suppress original output) will display lines twice.]]<br><br>The '''p''' instruction with the '''sed''' command is used to<br>'''print''' (i.e. ''display'') the contents of a text file.<br><br>
 +
# Issue the following Linux command:<br><span style="color:blue;font-weight:bold;font-family:courier;">sed 'p' data.txt</span><br><br>'''NOTE: You should notice that each line appears twice'''.<br><br>The reason why standard output appears twice is that the sed command<br>(without the '''-n option''') displays all lines regardless of an address used.<br><br>We will use '''pipeline commands''' to both display stdout to the screen and save to files<br>for <u>confirmation</u> of running these pipeline commands when run a '''checking-script''' later in this investigation.<br><br>
 +
# Issue the following Linux pipeline command:<br><span style="color:blue;font-weight:bold;font-family:courier;">sed -n 'p' data.txt | tee sed-1.txt</span><br><br>What do you notice? You should see only one line.<br><br>You can specify an '''address''' to display lines using the sed utility<br>(eg. ''line #'', '''line #s''' or range of '''line #s''').<br><br>
 +
# Issue the following Linux pipeline command:<br><span style="color:blue;font-weight:bold;font-family:courier;">sed -n '1 p' data.txt | tee sed-2.txt</span><br><br>You should see the first line of the text file displayed.<br>What other command is used to only display the first line in a file?<br><br>[[Image:sed-2.png|thumb|right|500px|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 | 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''' instruction is used to '''substitute''' text<br>(a 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 '''data.txt''' file<br>in another shell to confirm that the substitution occurred.<br><br>[[Image:sed-3.png|thumb|right|500px|Using the sed command with the '''-q''' 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.<br><br>
 +
# Issue the following Linux pipeline command:<br><span style="color:blue;font-weight:bold;font-family:courier;">sed '11 q' data.txt | 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 can use '''regular expressions''' to select lines that match a pattern. In fact,<br>the sed command was one of the <u>first</u> Linux commands that used regular expression.<br><br>The rules remain the same for using regular expressions as demonstrated in '''tutorial 9'''<br>except the regular expression must be contained within '''forward slashes'''<br>(eg. <span style="font-family:courier;font-weight:bold;">/regexp/</span> ).<br><br>[[Image:sed-4.png|thumb|right|400px|Using the sed command using regular expressions with '''anchors'''.]]
 +
# Issue the following Linux pipeline command:<br><span style="color:blue;font-weight:bold;font-family:courier;">sed -n '/^The/ p' data.txt | tee sed-6.txt</span><br><br>What do you notice?<br><br>
 +
# Issue the following Linux pipeline command:<br><span style="color:blue;font-weight:bold;font-family:courier;">sed -n '/d$/ p' data.txt | tee sed-7.txt</span><br><br>What do you notice?<br><br>The '''sed''' utility can also be used as a '''filter''' to manipulate text that<br>was generated from Linux commands.<br><br>[[Image:sed-5.png|thumb|right|400px|Using the sed command with '''pipeline''' commands.]]
 +
# Issue the following Linux pipeline command:<br><span style="color:blue;font-weight:bold;font-family:courier;">who | sed -n '/^[a-m]/ p' | tee sed-8.txt | more</span><br><br>What did you notice?<br><br>
 +
# Issue the following Linux pipeline command:<br><span style="color:blue;font-weight:bold;font-family:courier;">ls | sed -n '/txt$/ p' | tee sed-9.txt</span><br><br>What did you notice?<br><br>
 +
# Issue the following to run a checking script:<br><span style="color:blue;font-weight:bold;font-family:courier;">~uli101/week11-check-1</span><br><br>If you encounter errors, make corrections and '''re-run''' the checking script<br>until you receive a congratulations message, then you can proceed.<br><br>
  
=INVESTIGATION 1: CREATING A SHELL SCRIPT=
+
:In the next investigation, you will learn how to manipulate text using the '''awk''' utility.<br><br>
  
<br>
+
=INVESTIGATION 2: USING THE AWK UTILITY =
In this section, you will learn how to create and run a '''simple Bash Shell script'''.
 
  
 +
In this investigation, you will learn how to use the awk utility to manipulate text and generate reports.
  
 
'''Perform the Following Steps:'''
 
'''Perform the Following Steps:'''
  
# '''Login''' to your matrix account.<br><br>
+
# Change to your '''home''' directory and issue a command to '''confirm'''<br>you are located in your ''home'' directory.<br><br>
# Issue a command to '''confirm''' you are located in your '''home''' directory.<br><br>We want to create a Bash Shell script to welcome the user by their username.<br>Let's first provide some useful tips in terms of selecting an appropriate name for the shell script.<br><br>
+
# Issue a Linux command to create a directory called '''awk'''<br><br>
# Issue the following linux command to check if your intended shell script name<br>is already exists to be run automatically from the Bash shell:<br><span style="color:blue;font-weight:bold;font-family:courier;">which hello</span><br><br>You should notice that there is no output and therefore, this shell script name can be used.<br>On the other hand, if you wanted to create a file called sed, then the '''which sed''' command<br>would indicate it is already being used by the shell and that '''sed''' wouldn't be an appropriate shell script name to use.<br><br>
+
# Issue a Linux command to <u>change</u> to the '''awk''' directory and confirm you are located in the '''awk''' directory.<br><br>Let's download a database file that contains information regarding classic cars.<br><br>
# Use a '''text editor''' like '''vi''' or '''nano''' to create the text file called '''hello'''<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>
+
# Issue the following linux command ('''copy and paste''' to save time):<br><span style="color:blue;font-weight:bold;font-family:courier;">wget <nowiki>https://ict.senecacollege.ca/~murray.saul/uli101/cars.txt</nowiki></span><br><br>
# Enter the following two lines in your shell script, replacing "your-username" with your actual name:<br><span style="font-family:courier;">echo<br>echo "Hello $USER"<br>echo</span><br><br>'''NOTE:''' The variable called '''USER''' is an '''environment''' variable that contains the current user's login name.<Br>In this way if you wanted to share your shell script with other users, when they run the shell script<br>it will greet by <u>their</u> username. Using ''environment variables'' makes your shell script to be more "usable" by others.<br><br>
+
# Issue the '''cat''' command to quickly view the contents of the '''cars.txt''' file.<br><br>The "'''print'''" action (command) is the <u>default</u> action of awk to print<br>all selected lines that match a '''pattern'''.<br><br>This '''action''' (contained in braces) can provide more options<br>such as printing '''specific fields''' of selected lines (or records) from a database.<br><br>[[Image:awk-1.png|thumb|right|400px|Using the awk command to display matches of the pattern '''ford'''.]]
# Save your editing session and exit the text editor.<br><br>Instead of issuing the '''bash''' command followed by your shell script pathname as an ''argument'',<br>let's simply run it by its filename. This is the most common method of running shell scripts.<br><br>
+
# Issue the following linux command all to display all lines (i.e. records) in the '''cars.txt''' database that matches the pattern (or "make") called '''ford''':<br><span style="color:blue;font-weight:bold;font-family:courier;">awk '/ford/ {print}' cars.txt</span><br><br>We will use '''pipeline commands''' to both display stdout to the screen and save to files for <u>confirmation</u> of running these pipeline commands when run a '''checking-script''' later in this investigation.<br><br>
# Issue the following linux command to run your shell script in your current directory:<br><span style="color:blue;font-weight:bold;font-family:courier;">./hello</span><br><br>You should notice an error indicating you don't have permissions to run the file.<br>You need to first add execute permissions prior to running the shell script.<br><br>
+
# Issue the following linux pipeline command all to display records<br>in the '''cars.txt''' database that contain the pattern (i.e. make) '''ford''':<br><span style="color:blue;font-weight:bold;font-family:courier;">awk '/ford/' cars.txt | tee awk-1.txt</span><br><br>What do you notice? You should notice ALL lines displayed <u>without</u> using '''search criteria'''.<br><br>You can use ''builtin'' '''variables''' with the '''print''' command for further processing.<br>We 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 '''field number'''.]]'''$0''' - Current record (entire line)<br>'''$1''' - First field in record<br>'''$n''' - nth field in record<br>'''NR''' - Record Number (order in database)<br> '''NF''' - Number of fields in current record<br><br>For a listing of more variables, please consult your course notes.<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 hello</span><br><br>
+
# Issue the following linux pipeline command to display the '''model''', '''year''', '''quantity''' and price<br>in the '''cars.txt''' database for makes of '''chevy''':<br><span style="color:blue;font-weight:bold;font-family:courier;">awk '/chevy/ {print $2,$3,$4,$5}' cars.txt | tee awk-2.txt</span><br><br>Notice that a '''space''' is the delimiter for the fields that appear as standard output.<br><br>The '''tilde character''' '''~''' is used to search for a pattern or display standard output for a particular field.<br><br>
# Re-run your shell script: <span style="color:blue;font-weight:bold;font-family:courier;">./hello</span><br><br>Did you shell script run?<br><br>
+
# Issue the following linux pipeline command to display all '''plymouths''' ('''plym''')<br>by '''model name''', '''price''' and '''quantity''':<br><span style="color:blue;font-weight:bold;font-family:courier;">awk '$1 ~ /plym/ {print $2,$3,$4,$5}' cars.txt | tee awk-3.txt</span><br><br>You can also use '''comparison operators''' to specify conditions for processing with matched patterns<br>when using the awk command. Since they are used WITHIN the awk expression,<br>they are not confused with redirection symbols<br><br>[[Image:awk-3.png|thumb|right|400px|Using the awk command to display results based on '''comparison operators'''.]]'''<''' &nbsp;&nbsp;&nbsp;&nbsp;Less than<br>'''<=''' &nbsp;&nbsp;Less than or equal<br>'''>''' &nbsp;&nbsp;&nbsp;&nbsp;Greater than<br>'''>=''' &nbsp;&nbsp;Greater than or equal<br>'''==''' &nbsp;&nbsp;Equal<br>'''!=''' &nbsp;&nbsp;&nbsp;Not equal<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/scripts/week10-check-1</span><br><br>
+
# Issue the following linux pipeline command to display display the '''car make''', '''model''', '''quantity''' and '''price''' of all vehicles whose '''prices are less than $5,000''':<br><span style="color:blue;font-weight:bold;font-family:courier;">awk '$5 < 5000 {print $1,$2,$4,$5}' cars.txt | tee awk-4.txt</span><br><br>What do you notice?<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>
+
# Issue the following linux pipeline command to display display '''price''',<br>'''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;">awk '$5 < 5000 {print $5,$4,$2,$1}' cars.txt | tee awk-5.txt</span><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<br>how to add a '''she-bang line''' at the top of a shell script to force it to run in a specified shell.<br><br>
+
# Issue the following linux pipeline command to display the '''car make''',<br>'''year''' and '''quantity''' of cars that '''begin''' with the '''letter 'f'''':<br><span style="color:blue;font-weight:bold;font-family:courier;">awk '$1 ~ /^f/ {print $1,$2,$4}' cars.txt | tee awk-6.txt</span><br><br>[[Image:awk-4.png|thumb|right|400px|Using the awk command to display combined search results based on '''compound operators'''.]]Combined pattern searches can be made<br>by using '''compound operator''' symbols:<br><br>'''&&''' &nbsp;&nbsp;&nbsp;&nbsp;(and)<br>'''||''' &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(or)<br><br>
 +
# Issue the following linux pipeline command to list all '''fords'''<br>whose '''price is greater than $10,000''':<br><span style="color:blue;font-weight:bold;font-family:courier;">awk '$1 ~ /ford/ && $5 > 10000 {print $0}' cars.txt | tee awk-7.txt</span><br><br>
 +
# Issue the following linux command ('''copy and paste''' to save time):<br><span style="color:blue;font-weight:bold;font-family:courier;">wget <nowiki>https://ict.senecacollege.ca/~murray.saul/uli101/cars2.txt</nowiki></span><br><br>
 +
# Issue the '''cat''' command to quickly view the contents of the '''cars2.txt''' file.<br><br>
 +
# Issue the following linux pipeline command to display the '''year'''<br>and '''quantity''' of cars that '''begin''' with the '''letter 'f'''' for the '''cars2.txt''' database:<br><span style="color:blue;font-weight:bold;font-family:courier;">awk '$1 ~ /^f/ {print $2,$4}' cars2.txt | tee awk-8.txt</span><br><br>What did you notice?<br><br>The problem is that the '''cars2.txt''' database separates each field by a semi-colon (''';''') <u>instead</u> of '''TAB'''.<br>Therefore, it does not recognize the second and fourth fields.<br><br>You need to issue awk with the -F option to indicate that this file's fields are separated (delimited) by a semi-colorn.<br><br>
 +
# Issue the following linux pipeline command to display the '''year'''<br>and '''quantity''' of cars that '''begin''' with the '''letter 'f'''' for the '''cars2.txt''' database:<br><span style="color:blue;font-weight:bold;font-family:courier;">awk -F";" '$1 ~ /^f/ {print $2,$4}' cars2.txt | tee awk-9.txt</span><br><br>What did you notice this time?<br><br>
 +
# Issue the following to run a checking script:<br><span style="color:blue;font-weight:bold;font-family:courier;">~uli101/week11-check-2</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>
  
=INVESTIGATION 2: USING VARIABLES IN SHELL SCRIPTS =
+
= LINUX PRACTICE QUESTIONS =
  
In this section, you will learn how to use variables, positional and special parameters to assist you in creating adaptable shell scripts.
+
The purpose of this section is to obtain '''extra practice''' to help with '''quizzes''', your '''midterm''', and your '''final exam'''.
  
 +
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 to
 +
simulate a quiz:
  
 +
https://ict.senecacollege.ca/~murray.saul/uli101/uli101_week11_practice.docx
  
'''Perform the Following Steps:'''
+
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).
  
# Confirm that you are located in your '''home''' directory in your Matrix account.<br><br>
 
# Use a text editor to edit the shell script called '''hello'''<br><br>
 
# Add the following line to the bottom of the file:<br><span style="font-family:courier;">ps -o cmd= -p $$|cut -d" " -f1</span><br><br>'''NOTE:''' This command displays the '''name''' of the ''shell'' that the shell script<br>is running within.<br><br>
 
# '''Save''' your editing changes and '''exit''' your text editor.<br><br>
 
# Issue the following linux command to run this shell script with the Bourne Shell (i.e. '''sh'''):<br><span style="color:blue;font-weight:bold;font-family:courier;">sh hello</span><br><br>You should see the output of the command that you are located in shows '''sh''' (i.e. the '''Bourne Shell''').<br><br>'''NOTE:''' Due to the fact that shells (and their features) have '''evolved''' over a period of time,<br>an error may occur if you include a ''NEWER'' shell feature (e.g. ''Bash Shell'') in your shell script,<br>but run it in an ''OLDER'' shell (e.g. ''Bourne Shell'').<br><br>You can add a '''special comment''' to the BEGINNING of the FIRST line of your shell script to<br>'''force''' it to run in the shell you want (for example: the Bash shell).<br><br>
 
# Edit your '''hello''' shell script using a text editor.<br><br>
 
# Insert the following line at the '''beginning''' of the '''first''' line of your hello file:<br><span style="font-family:courier;">#!/bin/bash</span><br><br>This is referred to as a '''she-bang line'''. It forces this script to be run in the '''Bash Shell'''.<br>When your Bash Shell script finishes execution, you are returned to your current shell that you are using<br>(which in our case in Matrix, is still the Bash shell).<br><br>
 
# '''Save''' your editing changes and '''exit''' your text editor.<br><br>
 
# Issue the following linux command to run this shell script with the Bourne Shell (i.e. '''sh'''):<br><span style="color:blue;font-weight:bold;font-family:courier;">sh hello</span><br><br>You should notice that the shell name is now '''bash''' although you are trying to run it<br>in the ''Bourne Shell'' ('''sh'''). The "she-bang" line ''forces'' a new bash shell to be used to run your shell script.<br><br>
 
# It is a good idea to rename your shell script to include an '''extension''' to indicate that the file is a Bash Shell script file (referred to as a "''portable Bash shell script''"). <br>Issue the following linux command to rename your shell script file:<br><span style="color:blue;font-weight:bold;font-family:courier;">mv hello hello.bash</span><br><br>
 
# Run your renamed shell script for confirmation by issuing:<br><span style="color:blue;font-weight:bold;font-family:courier;">./hello.bash</span><br><br>
 
# Enter the following linux command to return to your Bash shell: <span style="color:blue;font-weight:bold;font-family:courier;">exit</span><br><br>
 
# Issue the following Linux command to confirm you have returned to the Bash shell: <span style="color:blue;font-weight:bold;font-family:courier;">echo $SHELL</span><br><br>Let's use some '''ENVIRONMENT variables''' in our Bash Shell script.<br><br>
 
# Use a text editor to edit the shell script called '''hello.bash'''<br><br>
 
# Add the following lines to the bottom of the file:<br><span style="font-family:courier;">echo<br>echo "The current directory location is: $PWD"<br>echo "The current user home directory is: $HOME<br>echo</span><br><br>
 
# Save your editing changes and exit your text editor.<br><br>
 
# Run your renamed shell script for confirmation by issuing:<br><span style="color:blue;font-weight:bold;font-family:courier;">./hello.bash</span><br><br>Take time to view the output and the values of the environment variables.<br><br>
 
# Issue the following linux command to add your current directory to the '''PATH''' environment variable:<br><span style="color:blue;font-weight:bold;font-family:courier;">PATH=$PATH:.</span><br><br>
 
# Issue the following linux command to confirm that the current directory "." has been added to the PATH environment variable:<br><span style="color:blue;font-weight:bold;font-family:courier;">echo $PATH</span><br><br>
 
# Issue the following to run your Bash shell script just by name:<br><span style="color:blue;font-weight:bold;font-family:courier;">hello.bash</span><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 the '''hello.bash''' shell script by just using the name.<br><br>What did you notice?<br><br>The setting of the '''PATH''' environment variable only worked in the current session only.<br>If you exit the current Matrix session, then the recently changed settings for environment variables will be lost.<br>You will in a <u>future</u> tutorial how to set environment variables in '''start-up''' files.<br><br><span style="color:red;">'''ATTENTION:''' Students will get FRUSTRATED when performing their '''assignment 3''' when their Bash shell scripts have errors. One major cause is the the OUTPUT of their Bash shell script when run does not '''EXACTLY match''' the required output for the correct Bash shell script. This requires that you CAREFULLY '''read''' the requirements of your Bash shell script and create it to the EXACT specifications.<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/scripts/week10-check-2 | 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>Let's create a Bash shell script that contain '''user-created variables'''.<br><br>
 
# Use a text editor to create a Bash shell script called '''user-variables.bash'''<br><br>
 
# Add the following lines to the beginning of this file:<br><span style="font-family:courier;">#!/bin/bash<br>age=25<br>readonly age<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>
 
# 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><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>
 
# 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;">#!/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>
 
# 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 the parameters may not be displayed properly since you did NOT provide any arguments when running the 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;">./parameters.bash 1 2 3 4 5 6 7 8</span><br><br>Take some time to view the results and how the parameters are changed when using the shift command. What do you notice?<br>
 
  
 +
'''Review Questions:'''
  
In the next investigation, you will use control-flow statements to allow your shell scripts to perform differently under different situations.
+
'''Part A: Display Results from Using the sed Utility'''
  
=INVESTIGATION 3: USING CONTROL FLOW STATEMENTS =
+
Note the contents from the following tab-delimited file called '''~murray.saul/uli101/stuff.txt''':
 +
(this file pathname exists for checking your work)
  
In this section, you will learn how to use control-flow statements to make your shell script behave differently under different situation.
+
<pre>
 +
Line one.
 +
This is the second line.
 +
This is the third.
 +
This is line four.
 +
Five.
 +
Line six follows
 +
Followed by 7
 +
Now line 8
 +
and line nine
 +
Finally, line 10
 +
</pre>
  
  
 +
Write the results of each of the following Linux commands for the above-mentioned file:
  
'''Perform the Following Steps:'''
 
  
: Before learning about logic and loop control-flow statements, you need to first learn about issuing test conditions using the '''test''' command.<br><br>
+
# <span style="font-family:courier;font-weight:bold">sed -n '3,6 p' ~murray.saul/uli101/stuff.txt</span><br><br>
# Confirm that you are located in your '''home''' directory in your Matrix account.<br><br>
+
# <span style="font-family:courier;font-weight:bold">sed '4 q' ~murray.saul/uli101/stuff.txt</span><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>
+
# <span style="font-family:courier;font-weight:bold">sed '/the/ d' ~murray.saul/uli101/stuff.txt</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 previously command issued (including the test command). If the status is '''zero''', then it indicates a TRUE value and if the status is '''non-zero''', then it indicates a FALSE value.<br><br>
+
# <span style="font-family:courier;font-weight:bold">sed 's/line/NUMBER/g' ~murray.saul/uli101/stuff.txt</span>
# 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 its 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>The value is non-zero (FALSE) since UPPERCASE characters 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 '''$?'''. What is the result? Why?<br><br>
 
# Issue the following linux command to test a condition involving numbers:<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 '''$?'''. '''NOTE:''' You will notice that something is '''wrong'''.<br>The exit status '''$?''' 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  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>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 contain the test condition within the square brackets. You need to have spaces between the brackets and the test condition; 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>You should notice an test error message.<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. You should notice that is works properly.<br><br>'''Let's now learn about control-flow statements:'''<br><br>'''Logic statements''' are used to create different paths or directions based on the result of testing conditions. In this tutorial, we will only focus on the '''if''' 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>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;">#!/bin/bash<br>clear<br>num1=5<br>num2=10<br>if [ $num1 -gt $num2 ]<br>then<br>&nbsp;&nbsp;&nbsp;echo "Greater Than"<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>
 
# 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;">#!/bin/bash<br>clear<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>
 
# 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: <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? We will learn about if-else and if-elif-else statements in a couple of weeks.<br><br>'''Loop statements''' are used to provide repetition in a shell script. In this tutorial, we will only focus on the '''for''' loop statement.<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>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;">#!/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>
 
# 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>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;">#!/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>
 
# 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/scripts/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 proceed.<br><br>Let's create a Bash shell script that contain '''user-created variables'''.<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)'''.<br><br>
 
  
= LINUX PRACTICE QUESTIONS =
 
  
The purpose of this section is to obtain '''extra practice''' to help with '''quizzes''', your '''midterm''', and your '''final exam'''.
+
'''Part B: Writing Linux Commands Using the sed Utility'''
  
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 to
+
Write a single Linux command to perform the specified tasks for each of the following questions.
simulate a quiz:
 
  
https://ict.senecacollege.ca/~murray.saul/uli101/uli101_week10_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).
+
# Write a Linux sed command to display only lines 5 to 9 for the file: '''~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>
  
  
'''Review Questions:'''
+
'''Part C: Writing Linux Commands Using the awk Utility'''
  
 +
Note the contents from the following tab-delimited file called '''~murray.saul/uli101/stuff.txt''':
 +
(this file pathname exists for checking your work)
  
'''PART A: WRITE BASH SHELL SCRIPT CODE'''
+
<pre>
 +
Line one.
 +
This is the second line.
 +
This is the third.
 +
This is line four.
 +
Five.
 +
Line six follows
 +
Followed by 7
 +
Now line 8
 +
and line nine
 +
Finally, line 10
 +
</pre>
  
'''Write the answer to each question below the question in the space provided.'''
 
  
 +
'''Write the results of each of the following Linux commands for the above-mentioned file:'''
  
# 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 the user for their '''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>
 
  
'''PART B: WALK-THRUS'''
+
# <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 the expected output from running each of the following Bash shell scripts You can assume that these Bash shell script files have execute permissions. Show your work.'''
 
  
:'''Walkthru #1:'''
+
'''Part D: Writing Linux Commands Using the awk Utility'''
  
:'''cat walkthru1.bash'''
 
<pre>
 
#!/usr/bin/bash
 
word1=”counter”
 
word2=”clockwise”
 
echo “The combined word is: $word2$word1”
 
</pre>
 
  
:WRITE OUTPUT FROM ISSUING:
+
Write a single Linux command to perform the specified tasks for each of the following questions.
:'''./walkthru1.bash'''
 
  
  
:'''Walkthru #2:'''
+
# 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: '''~/cars''' 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>
  
:'''cat walkthru2.bash'''
 
<pre>
 
#!/usr/bin/bash
 
echo “result1: $1”
 
echo “result2: $2”
 
echo “result3: $3”
 
echo “result 4:”
 
echo “$*”
 
</pre>
 
  
:WRITE OUTPUT FROM ISSUING:
 
:'''./walkthru2.bash apple orange banana'''
 
<br><br>
 
  
  
 
[[Category:ULI101]]
 
[[Category:ULI101]]

Latest revision as of 07:17, 29 April 2022

USING SED & AWK UTILTIES


Main Objectives of this Practice Tutorial

  • Use the sed command to manipulate text contained in a file.
  • List and explain several addresses and instructions associated with the sed command.
  • Use the sed command as a filter with Linux pipeline commands.
  • Use the awk command to manipulate text contained in a file.
  • List and explain comparison operators, variables and actions associated with the awk command.
  • Use the awk command as a filter with Linux pipeline commands.



Tutorial Reference Material

Course Notes
Linux Command/Shortcut Reference
YouTube Videos
Slides:


Text Manipulation: Commands:


Brauer Instructional Videos:

KEY CONCEPTS

Using the sed Utility

Usage:

Syntax: sed [-n] 'address instruction' filename


How it Works:

  • The sed command reads all lines in the input file and will be exposed to the expression
    (i.e. area contained within quotes) one line at a time.
  • The expression can be within single quotes or double quotes.
  • The expression contains an address (match condition) and an instruction (operation).
  • If the line matches the address, then it will perform the instruction.
  • Lines will display be default unless the –n option is used to suppress default display


Address:

  • Can use a line number, to select a specific line (for example: 5)
  • Can specify a range of line numbers (for example: 5,7)
  • Regular expressions are contained within forward slashes (e.g. /regular-expression/)
  • Can specify a regular expression to select all lines that match a pattern (e.g /^[0-9].*[0-9]$/)
  • If NO address is present, the instruction will apply to ALL lines


Sed.png

Instruction:

  • Action to take for matched line(s)
  • Refer to table on right-side for list of some
    common instructions and their purpose



Using the awk Utility

Usage:

awk [-F] 'selection-criteria {action}’ file-name


How It Works:

  • 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.
  • The –F option can be used to specify the default field delimiter (separator) character
    eg. awk –F”;” (would indicate a semi-colon delimited input file).


Selection Criteria

  • 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 ( > , >= , < , <= , == , != ).
  • 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.
    For example: NR >=1 && NR <= 5


Action (execution):

  • Action to be executed is contained within braces {}
  • 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)
    eg. {print NR,$0} (will print record number, then entire record).

INVESTIGATION 1: USING THE SED UTILITY

ATTENTION: Effective May 9, 2022 - this online tutorial will be required to be completed by Friday in week 11 by midnight
to obtain a grade of 2% towards this course


In this investigation, you will learn how to manipulate text using the sed utility.


Perform the Following Steps:

  1. Login to your matrix account and confirm you are located in your home directory.

  2. Issue a Linux command to create a directory called sed

  3. Issue a Linux command to change to the sed directory and confirm that you are located in the sed directory.

  4. Issue the following Linux command to download the data.txt file
    (copy and paste to save time):
    wget https://ict.senecacollege.ca/~murray.saul/uli101/data.txt

  5. Issue the more command to quickly view the contents of the data.txt file.
    When finished, exit the more command by pressing the letter q
    Issuing the p instruction without using the -n option (to suppress original output) will display lines twice.


    The p instruction with the sed command is used to
    print (i.e. display) the contents of a text file.

  6. Issue the following Linux command:
    sed 'p' data.txt

    NOTE: You should notice that each line appears twice.

    The reason why standard output appears twice is that the sed command
    (without the -n option) displays all lines regardless of an address used.

    We will use pipeline commands to both display stdout to the screen and save to files
    for confirmation of running these pipeline commands when run a checking-script later in this investigation.

  7. Issue the following Linux pipeline command:
    sed -n 'p' data.txt | tee sed-1.txt

    What do you notice? You should see only one line.

    You can specify an address to display lines using the sed utility
    (eg. line #, line #s or range of line #s).

  8. Issue the following Linux pipeline command:
    sed -n '1 p' data.txt | tee sed-2.txt

    You should see the first line of the text file displayed.
    What other command is used to only display the first line in a file?

    Using the sed command to display a range of lines.
  9. Issue the following Linux pipeline command:
    sed -n '2,5 p' data.txt | tee sed-3.txt

    What is displayed? How would you modify the sed command to display the line range 10 to 50?

    The s instruction is used to substitute text
    (a similar to method was demonstrated in the vi editor in tutorial 9).

  10. Issue the following Linux pipeline command:
    sed '2,5 s/TUTORIAL/LESSON/g' data.txt | tee sed-4.txt | more

    What do you notice? View the original contents of lines 2 to 5 in the data.txt file
    in another shell to confirm that the substitution occurred.

    Using the sed command with the -q 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.

  11. Issue the following Linux pipeline command:
    sed '11 q' data.txt | tee sed-5.txt

    What did you notice? How many lines were displayed
    before the sed command exited?

    You can use regular expressions to select lines that match a pattern. In fact,
    the sed command was one of the first Linux commands that used regular expression.

    The rules remain the same for using regular expressions as demonstrated in tutorial 9
    except the regular expression must be contained within forward slashes
    (eg. /regexp/ ).

    Using the sed command using regular expressions with anchors.
  12. Issue the following Linux pipeline command:
    sed -n '/^The/ p' data.txt | tee sed-6.txt

    What do you notice?

  13. Issue the following Linux pipeline command:
    sed -n '/d$/ p' data.txt | tee sed-7.txt

    What do you notice?

    The sed utility can also be used as a filter to manipulate text that
    was generated from Linux commands.

    Using the sed command with pipeline commands.
  14. Issue the following Linux pipeline command:
    who | sed -n '/^[a-m]/ p' | tee sed-8.txt | more

    What did you notice?

  15. Issue the following Linux pipeline command:
    ls | sed -n '/txt$/ p' | tee sed-9.txt

    What did you notice?

  16. Issue the following to run a checking script:
    ~uli101/week11-check-1

    If you encounter errors, make corrections and re-run the checking script
    until you receive a congratulations message, then you can proceed.

In the next investigation, you will learn how to manipulate text using the awk utility.

INVESTIGATION 2: USING THE AWK UTILITY

In this investigation, you will learn how to use the awk utility to manipulate text and generate reports.

Perform the Following Steps:

  1. Change to your home directory and issue a command to confirm
    you are located in your home directory.

  2. Issue a Linux command to create a directory called awk

  3. Issue a Linux command to change to the awk directory and confirm you are located in the awk directory.

    Let's download a database file that contains information regarding classic cars.

  4. Issue the following linux command (copy and paste to save time):
    wget https://ict.senecacollege.ca/~murray.saul/uli101/cars.txt

  5. Issue the cat command to quickly view the contents of the cars.txt file.

    The "print" action (command) is the default action of awk to print
    all selected lines that match a pattern.

    This action (contained in braces) can provide more options
    such as printing specific fields of selected lines (or records) from a database.

    Using the awk command to display matches of the pattern ford.
  6. Issue the following linux command all to display all lines (i.e. records) in the cars.txt database that matches the pattern (or "make") called ford:
    awk '/ford/ {print}' cars.txt

    We will use pipeline commands to both display stdout to the screen and save to files for confirmation of running these pipeline commands when run a checking-script later in this investigation.

  7. Issue the following linux pipeline command all to display records
    in the cars.txt database that contain the pattern (i.e. make) ford:
    awk '/ford/' cars.txt | tee awk-1.txt

    What do you notice? You should notice ALL lines displayed without using search criteria.

    You can use builtin variables with the print command for further processing.
    We will discuss the following variables in this tutorial:

    Using the awk command to print search results by field number.
    $0 - Current record (entire line)
    $1 - First field in record
    $n - nth field in record
    NR - Record Number (order in database)
    NF - Number of fields in current record

    For a listing of more variables, please consult your course notes.

  8. Issue the following linux pipeline command to display the model, year, quantity and price
    in the cars.txt database for makes of chevy:
    awk '/chevy/ {print $2,$3,$4,$5}' cars.txt | tee awk-2.txt

    Notice that a space is the delimiter for the fields that appear as standard output.

    The tilde character ~ is used to search for a pattern or display standard output for a particular field.

  9. Issue the following linux pipeline command to display all plymouths (plym)
    by model name, price and quantity:
    awk '$1 ~ /plym/ {print $2,$3,$4,$5}' cars.txt | tee awk-3.txt

    You can also use comparison operators to specify conditions for processing with matched patterns
    when using the awk command. Since they are used WITHIN the awk expression,
    they are not confused with redirection symbols

    Using the awk command to display results based on comparison operators.
    <     Less than
    <=   Less than or equal
    >     Greater than
    >=   Greater than or equal
    ==   Equal
    !=    Not equal

  10. Issue the following linux pipeline command to display display the car make, model, quantity and price of all vehicles whose prices are less than $5,000:
    awk '$5 < 5000 {print $1,$2,$4,$5}' cars.txt | tee awk-4.txt

    What do you notice?

  11. Issue the following linux pipeline command to display display price,
    quantity, model and car make of vehicles whose prices are less than $5,000:
    awk '$5 < 5000 {print $5,$4,$2,$1}' cars.txt | tee awk-5.txt

  12. Issue the following linux pipeline command to display the car make,
    year and quantity of cars that begin with the letter 'f':
    awk '$1 ~ /^f/ {print $1,$2,$4}' cars.txt | tee awk-6.txt

    Using the awk command to display combined search results based on compound operators.
    Combined pattern searches can be made
    by using compound operator symbols:

    &&     (and)
    ||        (or)

  13. Issue the following linux pipeline command to list all fords
    whose price is greater than $10,000:
    awk '$1 ~ /ford/ && $5 > 10000 {print $0}' cars.txt | tee awk-7.txt

  14. Issue the following linux command (copy and paste to save time):
    wget https://ict.senecacollege.ca/~murray.saul/uli101/cars2.txt

  15. Issue the cat command to quickly view the contents of the cars2.txt file.

  16. Issue the following linux pipeline command to display the year
    and quantity of cars that begin with the letter 'f' for the cars2.txt database:
    awk '$1 ~ /^f/ {print $2,$4}' cars2.txt | tee awk-8.txt

    What did you notice?

    The problem is that the cars2.txt database separates each field by a semi-colon (;) instead of TAB.
    Therefore, it does not recognize the second and fourth fields.

    You need to issue awk with the -F option to indicate that this file's fields are separated (delimited) by a semi-colorn.

  17. Issue the following linux pipeline command to display the year
    and quantity of cars that begin with the letter 'f' for the cars2.txt database:
    awk -F";" '$1 ~ /^f/ {print $2,$4}' cars2.txt | tee awk-9.txt

    What did you notice this time?

  18. Issue the following to run a checking script:
    ~uli101/week11-check-2

    If you encounter errors, make corrections and re-run the checking script until you
    receive a congratulations message, then you can proceed.

LINUX PRACTICE QUESTIONS

The purpose of this section is to obtain extra practice to help with quizzes, your midterm, and your final exam.

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 to simulate a quiz:

https://ict.senecacollege.ca/~murray.saul/uli101/uli101_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 ~murray.saul/uli101/stuff.txt: (this file pathname exists for checking your work)

Line one.
This is the second line.
This is the third.
This is line four.
Five.
Line six follows
Followed by 7
Now line 8
and line nine
Finally, line 10


Write the results of each of the following Linux commands for the above-mentioned file:


  1. sed -n '3,6 p' ~murray.saul/uli101/stuff.txt

  2. sed '4 q' ~murray.saul/uli101/stuff.txt

  3. sed '/the/ d' ~murray.saul/uli101/stuff.txt

  4. sed 's/line/NUMBER/g' ~murray.saul/uli101/stuff.txt


Part B: Writing Linux Commands Using the sed Utility

Write a single Linux command to perform the specified tasks for each of the following questions.


  1. Write a Linux sed command to display only lines 5 to 9 for the file: ~murray.saul/uli101/stuff.txt

  2. Write a Linux sed command to display only lines the begin the pattern “and” for the file: ~murray.saul/uli101/stuff.txt

  3. Write a Linux sed command to display only lines that end with a digit for the file: ~murray.saul/uli101/stuff.txt

  4. 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


Part C: Writing Linux Commands Using the awk Utility

Note the contents from the following tab-delimited file called ~murray.saul/uli101/stuff.txt: (this file pathname exists for checking your work)

Line one.
This is the second line.
This is the third.
This is line four.
Five.
Line six follows
Followed by 7
Now line 8
and line nine
Finally, line 10


Write the results of each of the following Linux commands for the above-mentioned file:


  1. awk ‘NR == 3 {print}’ ~murray.saul/uli101/stuff.txt

  2. awk ‘NR >= 2 && NR <= 5 {print}’ ~murray.saul/uli101/stuff.txt

  3. awk ‘$1 ~ /This/ {print $2}’ ~murray.saul/uli101/stuff.txt

  4. awk ‘$1 ~ /This/ {print $3,$2}’ ~murray.saul/uli101/stuff.txt


Part D: Writing Linux Commands Using the awk Utility


Write a single Linux command to perform the specified tasks for each of the following questions.


  1. Write a Linux awk command to display all records for the file: ~/cars whose fifth field is greater than 10000.

  2. Write a Linux awk command to display the first and fourth fields for the file: ~/cars whose fifth field begins with a number.

  3. Write a Linux awk command to display the second and third fields for the file: ~/cars for records that match the pattern “chevy”.

  4. Write a Linux awk command to display the first and second fields for all the records contained in the file: ~/cars