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Tutorial 11 - SED & AWK

7,344 bytes added, 13:58, 14 November 2021

→‎INVESTIGATION 2: 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:'''

# Change 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): cp ~osl640/cars.txt .

# 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 '''car make''', '''model''', '''quantity''' and '''price''' of vehicles whose '''prices are less than $5,000''': awk '$5 < 5000 {print $1,$2,$4,$5}' 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): cp ~osl640/tutorial11/cars2.txt .

# 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: ~osl640/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.

:: Complete the Review Questions sections to get additional practice.

= LINUX PRACTICE QUESTIONS =

Jason Michael Carman

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Tutorial 11 - SED & AWK

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