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Tutorial11: Sed & Awk Utilities

2,196 bytes added, 19:44, 10 May 2021

→‎INVESTIGATION 1: USING THE SED UTILITY

* 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):'''

* 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''' (~~like NR or~~ such as '''NR''' or "record number" ~~�representing~~ representing line number) eg. '''{print NR,$0}''' (will print record number, then entire record)��.

=INVESTIGATION 1: USING THE SED UTILITY=

'''ATTENTION''': Depending on your ULI101 instruction, you may be required to complete this tutorial for marks in the course. Please refer to your instructor's course notes in terms of marked assigned to the course. The due date for successfully completing this tutorial (i.e. '''tutorial 11''') is by '''Friday by midnight''' next week (i.e. '''Week 11'''). If your instructor has NOT assigned marks for completing this tutorial, you can perform it for practice purposes.

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

# 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~~ 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</span~~> <br~~>[[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 ~~or display the~~ ''' (i.e. ''display'') the contents of a text file. # Issue the following ~~linux~~ 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. # Issue the following ~~linux~~ 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''') ~~when using the sed utility~~. # Issue the following ~~linux~~ Linux pipeline command: sed -n '1 p' data.txt | tee sed-2.txt 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? [[Image:sed-2.png|thumb|right|500px|Using the sed command to display a '''range''' of lines.]]# Issue the following ~~linux~~ 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~~ 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~~ 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 rules remain~~ the ~~same for using regular expressions as demonstrated~~sed command was one of the <bru>~~in tutorial9 except the~~ first Linux commands that used regular expression ~~must be contained~~. ~~within~~ The rules remain the same for using regular expressions as demonstrated in '''~~delimiters~~tutorial 9''' ~~such as~~ except the regular expression must be contained within '''forward ~~slash~~ slashes''' (eg. /regexp/</~~" when using the sed utility~~span> ). [[Image:sed-4.png|thumb|right|400px|Using the sed command using regular expressions with '''anchors'''.]]# Issue the following ~~linux~~ Linux pipeline command: sed -n '/^The/ p' data.txt | tee sed-6.txt What do you notice? # Issue the following ~~linux~~ Linux pipeline command: sed -n '/d$/ p' data.txt | tee sed-7.txt What do you notice? The '''sed''' utility can also be used as a '''filter''' to manipulate text that was generated from ~~linux~~ Linux commands. [[Image:sed-5.png|thumb|right|400px|Using the sed command with '''pipeline''' commands.]]# Issue the following ~~linux~~ Linux pipeline command: who | sed -n '/^[a-m]/ p' | tee sed-8.txt | more What did you notice? # Issue the following ~~linux~~ Linux pipeline command: ls | sed -n '/txt$/ p' | tee sed-9.txt What did you notice?

# Issue the following to run a checking script: bash /home/murray.saul/myscripts/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.

# 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): wget <nowiki>https://ict.senecacollege.ca/~murray.saul/uli101/cars.txt</nowiki>

# Issue the '''~~more~~cat''' command to quickly view the contents of the '''cars.txt''' file.~~ When finished, exit the more command by pressing the letter q~~ The "'''print'''" action (command) is the default action of awkto print ~~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 a '''search criteria'''. You can use ~~these~~ ''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''' ('''~~plyms~~plym''') by '''model name''', '''price''' and '''quantity''': awk '$1 ~ /~~plyms~~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): 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: bash /home/murray.saul/myscripts/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.

:: After you complete the Review Questions sections to get additional practice, then work on your '''online assignment 3, section 2: Awk & Sed'''

Msaul

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