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Tutorial11: Sed & Awk Utilities

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 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 several comparison operators and variables 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
Course Notes:


Text Manipulation Man Pages


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.

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)
  • Can specify a regular expression to select all lines that match �(e.g /^[0-9].*[0-9]$/)
  • When using regular expressions, you must use forward slash(es) /
  • If NO address is present, the instruction will apply to ALL lines
 
Common instructions to take action if text matches an address.

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 options '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

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.)
  • There are built-in variables that can be used in the awk expression (for example: NR, NF, FILENAME, etc.)
  • You can use the -F option with the awk command to specify the field delimiter.

INVESTIGATION 1: USING THE SED UTILITY


In this section, 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 (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

  6. The p instruction with the sed command is used to print or display the contents of a text file.
    Issue the following linux command:
    sed 'p' data.txt

    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 if they had been specified as a pattern.

    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 can specify an address (line #, line #s or range of line #s) when using the sed utility.

  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.

  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 2 to 5?

    The s instruction is used to substitute patterns (similar to method demonstratedin vi editor).

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

    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.

    The q instruction terminates or quits the execution of the sed utility as soon as it 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?

    You can use regular expressions to select lines that match a pattern. The rules remain the same for using regular expressions as demonstrated in lab8 except the regular expression must be contained within delimiters such as the forward slash "/" when using the sed utility.

  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.

  14. Issue the following linux pipeline command:
    ls | sed -n '/txt$/ p' | tee sed-8.txt

    What did you notice?

  15. Issue the following linux pipeline command:
    who | sed -n '/^[a-m]/ p' | tee sed-9.txt | more

    What did you notice?

  16. Issue the following to run a checking script:
    bash /home/murray.saul/scripts/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 section, 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.

  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 more 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 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.

  6. Issue the following linux command all to display records in the "cars.txt" database that contain the make "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 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 variables with the "print" action for further processing. We will discuss the following variables in this tutorial:

    $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.

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

  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.

  9. Issue the following linux pipeline command to display all plymouths (plyms) by model name, price and quantity:
    awk '/chevy/ {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

    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 number, quantity and price of all vehicles that are prices 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 the car make, model number, quantity and price of all vehicles that are prices less than $5,000:
    awk '$5 < 5000 {print $1,$2,$4,$5}' cars.txt | tee awk-5.txt

    The symbol tilde ~ is used to match a pattern for a particular field number.

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

    Compound criteria symbols can be used to join search statements together

    Compound Operators:

    &&     (and)
    ||        (or)

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

  14. Issue the following to run a checking script:
    bash /home/murray.saul/scripts/week11-check-2

  15. 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

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