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Tutorial10: Shell Scripting - Part 1

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=~~INTRODUCTION TO SHELL SCRIPTING~~USING SED & AWK UTILTIES=

===Main Objectives of this Practice Tutorial===

:* ~~Understand~~ Use the ~~process for planning prior~~ '''sed''' command to ~~writing~~ '''manipulate text''' contained in a ~~shell script~~file.

:* ~~Understand~~ List and explain several '''addresses''' and '''instructions''' associated with the ~~purpose of a she-bang line contained at the top of a shell script~~'''sed''' command.

:* ~~Setting permissions for~~ Use the '''sed''' command as a ~~shell script and properly execute a shell script~~'''filter''' with Linux pipeline commands.

:* ~~Understand and use environment and user-defined variables within~~ Use the '''awk''' command to '''manipulate text''' contained in a ~~shell script~~file.

:* ~~Understand~~ List and explain '''comparison operators''', '''variables''' and '''actions''' associated with the ~~purpose of control flow statements used with shell scripts~~'''awk''' command.

:* Use the ~~test~~ '''awk''' command ~~to test various conditions~~as a '''filter''' with Linux pipeline commands. ~~:* Use the if logic statement and the for loop statement within shell scripts.~~

===Tutorial Reference Material===

|- valign="top" style="padding-left:15px;"

|colspan="2" |~~Course Notes~~'''Slides''':<ul><li>Week 11 Lecture 1 Notes: [[Media:ULI101-Week11.1.pdf | PDF]] | [https://~~ict~~matrix.senecacollege.ca/~~~murray~~chris.~~saul~~johnson/~~uli101~~ULI101/ULI101-Week11.1.pptx PPTX]</li><li>Week 11 Lecture 2 Notes: [[Media:ULI101-~~Week10~~Week11.2.pdf | PDF]] | [https://~~ict~~matrix.senecacollege.ca/~~~murray~~jason.~~saul~~carman/~~uli101~~slides/ULI101-~~Week10~~Week11.2.pptx PPTX] </li></ul>

| style="padding-left:15px;" |~~Shell Scripting~~'''Text Manipulation:'''* [https://www.digitalocean.com/community/tutorials/the-basics-of-using-the-sed-stream-editor-to-manipulate-text-in-linux Purposeof using the sed utility]* ~~Planning a Shell Script~~* Executing a Shell Script ~~Variables~~* Environment * User Defined[https://www.digitalocean.com/community/tutorials/how-to-use-the-awk-language-to-manipulate-text-in-linux Purpose of using the awk utility]

| style="padding-left:15px;"|~~Control Flow Statements~~'''Commands:'''* ~~Purpose~~[https://man7.org/linux/man-pages/man1/sed.1p.html sed]* ~~test command~~* if statement* for loop[https://man7.org/linux/man-pages/man1/awk.1p.html awk]

|colspan="1" style="padding-left:15px;" width="30%"|'''Brauer Instructional Videos:'''<ul><li>[https://www.youtube.com/watch?v=~~kxEP-KUhOSg~~npU6S61AIko&list=PLU1b1f-2Oe90TuYfifnWulINjMv_Wr16N&index=~~5 Introduction to Shell Scripting~~14 Using the sed Utility]</li><li>[https://www.youtube.com/watch?v=~~XVTwbINXnk4~~OV3XzjDYgJo&list=PLU1b1f-2Oe90TuYfifnWulINjMv_Wr16N&index=6 13 Using ~~Variables and Control Flow Statements in Shell Scripting~~the awk Utility]</ul>

|}

= KEY CONCEPTS =

~~A shell script is a computer program designed to be run by the Unix shell, a command-line interpreter. 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===~~

~~It is recommended to~~ '''~~plan~~Usage:''' out on a piece of paper the purpose of the shell script. 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. Finally, you can listing the steps to process the INPUT to provide the OUTPUT (including file storage). In the case, you start with the diagram, then generate a list of steps that will help you code your shell script.

~~Once you have planned your shell script by listing the sequence of steps in your script, you need to create a file that will contain your Linux commands.~~'''Syntax: sed [-n] 'address instruction' filename'''

NOTE: Avoid using filenames of already existing Linux Commands to avoid confusion. Using shell script filenames that include the file extension of the shell that the script will run within is recommended.

~~===Using Variables~~ '''How it Works:''' * The sed command reads all lines in ~~Shell Scripts===~~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

x

[[Image:sed.png|right|500px|]]

'''Instruction:'''

*'''Action''' to take for matched line(s)

*Refer to table on right-side for list of some '''common instructions''' and their purpose

===Using ~~Control Flow Statements in Shell Scripts~~the awk Utility===

x

~~=INVESTIGATION 1~~'''Usage: ~~CREATING A SHELL SCRIPT=~~'''

<brspan style="color:blue;font-weight:bold;font-family:courier;">awk [-F] 'selection-criteria {action}’ file-name~~In this section, you will learn how to ...~~

'''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 '''!~'''~~Perform the Following Steps~~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).~~# x~~* 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):'''

In * 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 ~~next investigation~~fields contained in the record (line).* The parameters '''$1''', ~~you will .~~'''$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 21: USING ~~VARIABLES IN SHELL SCRIPTS~~ THE SED UTILITY=

In '''ATTENTION''': Effective '''May 9, 2022''' - this ~~section, you~~ online tutorial will ~~learn how~~ 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:'''

# x'''Login''' to your matrix account and confirm you are located in your '''home''' directory. # Issue a Linux command to create a directory called '''sed''' # Issue a Linux command to change to the '''sed''' directory and confirm that you are located in the '''sed''' directory. # Issue the following Linux command to download the data.txt file ('''copy and paste''' to save time): wget <nowiki>https://ict.senecacollege.ca/~murray.saul/uli101/data.txt</nowiki> # 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[[Image:sed-1.png|thumb|right|300px|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. In # 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 ~~next~~ screen and save to files for confirmation of running these pipeline commands when run a '''checking-script''' later in this investigation. # 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'''). # 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? [[Image:sed-2.png|thumb|right|500px|Using the sed command to display a '''range''' of lines.]]# 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). # 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. [[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. # Issue the following Linux pipeline command: sed '11 q' data.txt | tee sed-5.txt What did you ~~will~~ 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/ ). [[Image:sed-4.png|thumb|right|400px|Using the sed command using regular expressions with '''anchors'''.]]# Issue the following Linux pipeline command: sed -n '/^The/ p' data.txt | tee sed-6.txt What do you notice? # Issue the following Linux pipeline command: sed -n '/d$/ p' data.txt | tee sed-7.txt What do you notice? The '''sed''' utility can also be used as a '''filter''' to manipulate text that was generated from Linux commands. [[Image:sed-5.png|thumb|right|400px|Using the sed command with '''pipeline''' commands.]]# Issue the following Linux pipeline command: who | sed -n '/^[a-m]/ p' | tee sed-8.txt | more What did you notice? # Issue the following Linux pipeline command: ls | sed -n '/txt$/ p' | tee sed-9.txt What did you notice? # 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.

~~=INVESTIGATION 3~~: ~~USING CONTROL FLOW STATEMENTS IN SHELL SCRIPTS =~~ In ~~this section~~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:'''

# xChange to your '''home''' directory and issue a command to '''confirm''' you are located in your ''home'' directory. # Issue a Linux command to create a directory called '''awk''' # 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. # Issue the following linux command ('''copy and paste''' to save time): wget <nowiki>https://ict.senecacollege.ca/~murray.saul/uli101/cars.txt</nowiki> # 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. [[Image:awk-1.png|thumb|right|400px|Using the awk command to display matches of the pattern '''ford'''.]]# Issue the following linux command all to display all lines (i.e. records) in the '''cars.txt''' database that matches the pattern (or "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. # 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: [[Image:awk-2.png|thumb|right|400px|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. # 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. # 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 [[Image:awk-3.png|thumb|right|400px|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 # 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? # 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 # 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 [[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 by using '''compound operator''' symbols: '''&&'''     (and) '''||'''        (or) # 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 # Issue the following linux command ('''copy and paste''' to save time): wget <nowiki>https://ict.senecacollege.ca/~murray.saul/uli101/cars2.txt</nowiki> # Issue the '''cat''' command to quickly view the contents of the '''cars2.txt''' file. # 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. # 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? # 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 =

simulate a quiz:

https://ict.senecacollege.ca/~murray.saul/uli101/~~uli101_week10_practice~~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) <pre>Line one.This is the second line.This is the third.This is line four.Five.Line six followsFollowed by 7Now line 8and line nineFinally, line 10</pre> Write the results of each of the following Linux commands for the above-mentioned file: # xsed -n '3,6 p' ~murray.saul/uli101/stuff.txt # x sed '4 q' ~murray.saul/uli101/stuff.txt # xsed '/the/ d' ~murray.saul/uli101/stuff.txt # xsed '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. # xWrite a Linux sed command to display only lines 5 to 9 for the file: '''~murray.saul/uli101/stuff.txt''' # xWrite a Linux sed command to display only lines the begin the pattern “and” for the file: '''~murray.saul/uli101/stuff.txt''' # xWrite a Linux sed command to display only lines that end with a digit for the file: '''~murray.saul/uli101/stuff.txt''' # xWrite 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) <pre>Line one.This is the second line.This is the third.This is line four.Five.Line six followsFollowed by 7Now line 8and line nineFinally, line 10</pre> '''Write the results of each of the following Linux commands for the above-mentioned file:''' # awk ‘NR == 3 {print}’ ~murray.saul/uli101/stuff.txt # awk ‘NR >= 2 && NR <= 5 {print}’ ~murray.saul/uli101/stuff.txt # awk ‘$1 ~ /This/ {print $2}’ ~murray.saul/uli101/stuff.txt # 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. # Write a Linux awk command to display all records for the file: '''~/cars''' whose fifth field is greater than 10000. # Write a Linux awk command to display the first and fourth fields for the file: '''~/cars''' whose fifth field begins with a number. # Write a Linux awk command to display the second and third fields for the file: '''~/cars''' for records that match the pattern “chevy”. # Write a Linux awk command to display the first and second fields for all the records contained in the file: '''~/cars'''

[[Category:ULI101]]

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