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Tutorial 9 - Regular Expressions

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~~Content under development~~

=USING REGULAR EXPRESSIONS=

= INVESTIGATION 1: SIMPLE & COMPLEX REGULAR EXPRESSIONS =

'''ATTENTION''': The due date for successfully completing this tutorial (i.e. tutorial 89) is by Friday, ~~December 15~~ April 21 @ 11:59 PM (Week 14).

In this investigation, you will learn how to use the '''grep''' command with '''simple and complex regular expressions''' to help search for ''patterns'' contained in text files.

# '''Login''' to your matrix account.

# Issue a Linux command to '''confirm''' you are located in your '''home''' directory. The '''wget''' command is used to download files from the Internet to your shell. This will be useful to download '''text files''' and '''data files''' that we will be using in this tutorial. # Issue the following linux Linux command to '''~~download~~copy''' a text file to your '''home''' directory: ~~wget <nowiki>https://ict.senecacollege.ca/~~cp ~~~murray.saul~~osl640/~~uli101~~tutorial9/textfile1.txt~~</nowiki>~~.

# View the contents of the '''textfile1.txt''' file using the '''more''' command see what data is contained in this file. Although there are several Linux commands that use regular expressions, we will be using the '''grep''' command for this investigation. [[Image:regexps-1.png|thumb|right|250px|Output of '''grep''' command matching simple regular expression "'''the'''" (only lowercase). Notice the pattern matches larger words like "'''their'''" or "'''them'''".]]

#Issue the following Linux command to match the pattern '''the''' within '''textfile1.txt''': grep "the" textfile1.txt Take a few moments to view the output and observe the matched patterns.

# Issue the following Linux command to create the '''regexps''' directory: mkdir ~/regexps

# Change to the '''regexps''' directory and confirm that you have moved to this directory.

# First, issue the following Linux command to ~~download~~ copy another data file called '''numbers1.dat''': ~~wget <nowiki>https://ict.senecacollege.ca/~~cp ~~~murray.saul~~osl640/~~uli101~~tutorial9/numbers1.dat~~</nowiki>~~.

# View the contents of the '''numbers.dat''' file using the '''more''' command and quickly view the contents of this file. You should notice '''valid''' and '''invalid''' numbers contained in this file. When finished, exit the more command.

# Issue the following linux pipeline command to display only '''whole''' numbers (i.e. no '''+''' or '''-''' sign): grep "^[0-9]*$" numbers1.dat | tee faulty.txt You may have noticed that the command '''does not entirely work'''. You may notice an '''empty line''' (which is NOT a whole number). This occurs since the * regular expression symbol represents ZERO or MORE occurrences of a number. You can use an additional numeric character class with the * regular expression symbol to search for one or more occurrences of a number.

# Issue the following Linux pipeline command to display only '''signed''' integers: grep "^[+-][0-9][0-9]*$" numbers1.dat | tee signed.txt What did you notice? Positive and negative numbers display, not '''unsigned''' numbers. [[Image:regexps-8.png|thumb|right|300px|Simultaneous '''anchoring''' of regular expressions using '''character class''' and '''zero or more occurrences''' to display '''signed''' and '''unsigned''' integers.]]

# Issue the following Linux pipeline command to display '''signed''' or '''unsigned integers''': grep "^[+-]*[0-9][0-9]*$" numbers1.dat | tee all.txt Did this command work?

# Issue the following command to check that you created those hard links: ~~~uli101~~osl640/week9-check-1 If you encounter errors, then view the feedback to make corrections, and then re-run the checking script. If you receive a congratulation message that there are no errors, then proceed with this tutorial. You can also use the '''grep''' command using ''regular expression'' as a '''filter''' in pipeline commands.

# Issue the following Linux pipeline command: ls | grep "[0-9].*dat$" What did this pipeline display?

# Issue the following Linux pipeline command: ls | grep "[a-z].*txt$" What did this pipeline display?

= INVESTIGATION 2: EXTENDED REGULAR EXPRESSIONS =

In this investigation, you will learn how to use '''extended regular expressions''' with the '''egrep''' command to further refine your search patterns.

'''Perform the Following Steps:'''

# Make certain that you are located in your '''~/regexps''' directory on your ''Matrix'' account.

# Issue the following Linux command to copy another data file called '''numbers2.dat''': cp ~osl640/tutorial9/numbers2.dat .

# View the contents of the '''numbers2.dat''' file using the '''more''' command and quickly view the contents of this file. You should notice ''valid'' and ''invalid'' numbers contained in this file. When finished, exit the more command. [[Image:eregexps-1.png|thumb|right|300px|'''Weakness''' of '''complex''' regular expressions that do not '''limit''' the number of '''positive''' or '''negative''' signs.]]

# Issue the following Linux command to display '''signed''' or '''unsigned integers''': grep "^[+-]*[0-9][0-9]*$" numbers2.dat You should notice '''multiple''' '''+''' or '''-''' '''signs''' appear prior to some numbers. This occurs since you are searching or one or MORE occurrences of a + or - sign. Using '''extended regular expression''' symbols to specify '''minimum''' and '''maximum''' repetitions: '''{min,max}''' can solve that problem.

# Issue the following Linux command (using extended regular expression symbols) to display '''signed''' or '''unsigned integers''': grep "^[+-]{0.1}[0-9]{1,}$" numbers2.dat '''NOTE: No output will be displayed! Why?''' This is due to the fact that the '''grep command was NOT issued correctly to use extended regular expression symbols'''. You would need to issue either '''grep -E''', or just issue the '''egrep''' command. The egrep command works with '''all''' regular expression symbols, and should be used in the future instead of the older grep command. 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 using '''egrep''' instead of ''grep'': egrep "^[+-]{0,1}[0-9]{1,}$" numbers2.dat | tee better-number1.txt [[Image:eregexps-2.png|thumb|right|300px|Using '''extended''' regular expression symbols (such as '''repetition''') to refine matches of ''signed'' and ''unsigned'' integers.]]You should have noticed that the command worked correctly this time because you used the '''egrep''' command. '''NOTE:''' With extended regular expressions, the '''?''' symbol can be used to represent the '''{0,1}''' repetition symbols and the '''+''' symbol can be used to represent the '''{1,}''' repetition symbols

# Issue the following Linux pipeline command using the repetition shortcuts "+" and "?": egrep "^[+-]?[0-9]+$" numbers2.dat | tee better-number2.txt You should have seen the '''same results''', but less typing was required.

# Issue the following Linux pipeline command to display '''signed''', '''unsigned''', '''whole''', and '''decimal''' numbers: egrep "^[+-]{0,1}[0-9]{1,}[.]{0,1}[0-9]*$" numbers2.dat | tee better-number3.txt Were all signed and unsigned intergers and decimal numbers displayed?

# Issue the follwoing command to check that you correctly issued those ''Linux pipeline commands'': ~osl640/week9-check-2 If you encounter errors, then view the feedback to make corrections, and then re-run the checking script. If you receive a congratulation message that there are no errors, then proceed with this tutorial. You can also use extended regular expression symbols for '''grouping'''. For example, you can search for repetitions of GROUPS of characters (like a word) as opposed to just a single character or a GROUP of numbers as opposed to a single digit.

# Issue the following linux pipeline command to download another data file called '''words.dat''': cp ~osl640/tutorial9/words.dat .

# View the contents of the '''words.dat''' file using the '''more''' command and quickly view the contents of this file. Within this file, you should notice some lines that contain repetitions of words. When finished, exit the more command.

# Issue the following linux pipeline command to display '''two or more occurrences''' of the word "the": egrep -i "(the){2,}" words.dat | tee word-search1.txt more '''NOTE: No output is displayed! Why?''' This is due to the fact that a space should be included at the end of the word "'''the'''". Usually words are separated by spaces; therefore, there were no matches since there were not occurrences of "thethe" as opposed to "'''the the'''" (i.e. no space after repetition of the pattern).

# Reissue the previous pipeline command with the word the followed by a '''space''' within the brackets: egrep -i "(the ){2,}" words.dat | tee word-search2.txt [[Image:eregexps-3.png|thumb|right|330px|Using '''extended''' regular expression symbols (such as '''grouping''') to refine matches of repetition of '''words''' (as opposed to ''characters'').]]The "|" (or) symbol (same symbol as "pipe") can be used within the grouping symbols to allow matching of additional groups of characters. Again, it is important to follow the character groupings with the space character

# Issue the following linux pipeline command to search for '''two or more occurrences''' of the word "'''the '''" or '''two or more occurrences''' of the word "'''and '''": egrep -i "(the |and ){2,}" words.dat | tee word-search3.txt

# Issue the following Linux command to check that you correctly issued those ''Linux pipeline commands'' using the '''tee''' command to create those text files: ~osl640/week9-check-3 If you encounter errors, then view the feedback to make corrections, and then re-run the checking script. If you receive a congratulation message that there are no errors, then proceed with this tutorial. Let's issue a Linux '''pipeline''' command using the '''egrep''' command as a '''filter''' using both '''complex''' and '''extended''' regular expressions.

# Issue the following Linux pipeline command: ls | egrep "[a-z]{1,}.*[0-9]" What did this Linux pipeline command display?

: The '''grep''' and '''egrep''' Linux commands are NOT the only Linux commands that use regular expressions. In the next investigation, you will apply regular expressions to a number of Linux commands that you already learned in this course.

: You can proceed to INVESTIGATION 3

= INVESTIGATION 3: OTHER COMMANDS THAT USE REGULAR EXPRESSIONS =

In this investigation, you will see commands other than '''grep''' or '''egrep''' that can use regular expressions.

'''Perform the Following Steps:'''

# Make certain that you are located in your '''~/regexps''' directory on your ''Matrix'' account.

# Let's look at using regular expressions with the '''man''' command. Issue the following linux command : man ls [[Image:other-re-1.png|thumb|right|300px|Entering '''/sort''' in the '''man''' command can search for the string "'''sort'''".]]

# We want to search for an option that can sort the file listing. Type the following regular expression below and press '''ENTER''': /sort '''FYI:''' The '''grep''' and '''egrep''' Linux commands contain the regular expressions within quotes, but '''most''' other Linux commands specify regular expressions using '''forward slashes''' (e.g. /regular expression   or   /regular expression/).

# Scroll throughout the man pages for the ls command to view matches for the pattern "'''sort'''" (You can press '''SPACE''' or key combination '''alt-b''' to move forward and backwards one screen respectively).

# Press the letter q to '''exit''' the ''man'' pages for '''ls'''. Let's use regular expressions with the '''less''' command.

# Issue the following Linux command to copy another data file called '''large-file.txt''': cp ~osl640/tutorial9/large-file.txt . [[Image:other-re-2.png|thumb|right|300px|Entering '''/uli101''' in the '''less''' command can display all matches of "'''uli101'''" throughout the text file. This is just sample output, you will be searching for '''osl640''' instead.]]

# Issue the following Linux command to view the contents of the '''large-file.txt''': less large-file.txt

#We want to search for a pattern '''osl640''' within this text file. Type the following regular expression and press ENTER: /osl640 You should see the pattern "osl640" throughout the text file.

# Press the letter q to exit the '''less''' command.

# Try the same search techniques with the '''more''' command. Does it work the same for the ''less'' command? [[Image:other-re-3.png|thumb|right|300px|Entering '''/uli101''' in the '''vi''' command can search for the string "'''uli101'''". This is just sample output, you will be searching for '''osl640''' instead.]]Let's learn how to perform a simple '''search and replace''' within the '''vi''' utility by using regular expressions.

# Issue the following Linux command to edit the '''large-file.txt''' file: vi large-file.txt Let's first perform a simple search within this text file.

# Press the '''ESC''' key to make certain you are in '''COMMAND''' mode.

# Type the following and press '''ENTER''': /osl640 You should notice the pattern "'''osl640'''" highlighted for ALL occurrences in this text file. Let's '''search''' for the '''osl640''' pattern, and '''replace''' it in capitals (i.e '''OSL640'''). In vi, to issue a command, you need to enter '''LAST LINE''' MODE then issue a command. Let's issue a command from '''LAST LINE''' MODE to search and replace '''osl640''' to '''OSL640'''. [[Image:other-re-4.png|thumb|right|500px|In l'''ast line''' MODE in the '''vi''' text editor, issuing a command using regular expressions to convert '''uli101''' to '''ULI101'''. This is just sample output, you will be searching for '''osl640''' instead.]]

# Making certain that you are '''COMMAND''' MODE in vi, type the following and press '''ENTER''': :%s/osl640/OSL640/g '''NOTE:''' The letter '''g''' after the replace regular expression represents "'''global'''" and will replace ALL occurrences of osl640 in the text document (as opposed to replacing the first occurrence for every line).

# Type the following (in uppercase letters) and press '''ENTER''': /OSL640 You should notice the pattern "'''OSL640'''" highlighted for ALL occurrences in this text file.

# Navigate throughout the text file to confirm that ALL occurrences of '''osl640''' have been replaced with '''OSL640'''.

# Save changes to your vi editing session and exit by typing the following and pressing ENTER: :x

: After you complete the '''Review Questions''' section to get additional practice.

= LINUX PRACTICE QUESTIONS =

== REVIEW QUESTIONS: SIMPLE & COMPLEX REGULAR EXPRESSIONS ==

Here is a link to the [https://matrix.senecacollege.ca/~osl640/questions/osl640_command_practice_9a.docx MS Word Document of ALL of the questions] displayed below but with extra room to answer on the document to simulate a quiz.

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).

'''Part A: Display Results from Linux Commands using Simple & Complex Regular Expressions'''

Note the contents from the following tab-delimited file called '''~osl640/cars''':

<pre>

Plym fury 77 73 2500

chevy nova 79 60 3000

ford mustang 65 45 10003

volvo gl 78 102 9850

ford ltd 83 15 10507

chevy nova 80 50 3503

fiat 600 65 115 450

honda accord 81 30 6000

ford thundbd 84 10 17000

toyota tercel 82 180 755

chevy impala 65 85 1553

ford bronco 83 25 9505

</pre>

Write the results of each of the following Linux commands using regular expressions for the above-mentioned file.

1. grep plym ~osl640/cars

2. grep -i fury ~osl640/cars

3. grep “^[m-z]” ~osl640/cars

4. grep -i “^[m-z]” ~osl640/cars

5. grep “3$” ~mosl640/cars

6. grep -i “c.*5$” ~osl640/cars

'''Part B: Writing Linux Commands Using Regular Expressions'''

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

7. Write a Linux command to display all lines in the file called '''~/text.txt''' that contains the pattern:

the

8. Write a Linux command to display all lines in the file called '''~/text.txt''' that contains the word:

the

9. Write a Linux command to display all lines in the file called '''~/text.txt''' that begin with a number.

10. Write a Linux command to display all lines in the file called '''~/text.txt''' that end with a letter

(either upper or lowercase).

11. Write a Linux command to display all lines in the file called '''~/text.txt''' that begin and end with a number.

12. Write a Linux command to display all lines in the file called '''~/text.txt''' that contains exactly 3 characters that can be anything.

13. Write a Linux command to display all lines in the file called '''~/text.txt''' that contains exactly 3 numbers.

14. Write a Linux command to display all lines in the file called '''~/text.txt''' that contains 1 or more “C” characters.

== REVIEW QUESTIONS: REGULAR EXPRESSIONS (INCLUDING EXTENDED REGULAR EXPRESSIONS) ==

Here is a link to the [https://matrix.senecacollege.ca/~osl640/questions/osl640_command_practice_9B.docx MS Word Document of ALL of the questions] displayed below but with extra room to answer on the document to simulate a quiz.

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).

'''Part A: Display Results from Linux Commands using Regular Expressions'''

Note the contents from the following tab-delimited file called '''~murray.saul/uli101/numbers.txt''':

<pre>

+123

---34

+++++++++++17

-45

45p8

25.6

11

</pre>

Write the results of each of the following Linux commands using regular expressions for the above-mentioned file.

1. grep "^[-+]" ~osl640/tutorial9/numbers.txt

2. grep "^[-+]*.[0-9]" ~osl640/tutorial9/numbers.txt

3. grep "^[+-]?[0-9]" ~osl640/tutorial9/numbers.txt    (Why?)

4. egrep "^[+-]?[0-9]" ~osl640/tutorial9/numbers.txt

5. egrep "^[+-]?[0-9]+$" ~osl640/tutorial9/numbers.txt

6. egrep "^[+-]?[0-9]+[.]?[0-9]+$" ~osl640/tutorial9/numbers.txt

'''Part B: Writing Linux Commands Using Regular Expressions'''

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

7. Write a Linux command to display all lines in the file called '''~/data.txt''' that begins with 1 or more occurrences of an UPPERCASE letter.

8. Write a Linux command to display all lines in the file called '''~/data.txt''' that ends with 3 or more occurrences of the number 6

9. Write a Linux command to display all lines in the file called '''~/data.txt''' that begins with 2 or more occurrences of the word “the” (upper or lower case).

10. Write a Linux command to display all lines in the file called '''~/data.txt''' that begins with 2 or more occurrences       of the word “the” or the word “but” (upper or lower case).

11. Write a Linux command to display all lines in the file called '''~/data.txt''' that begins with a minimum of 2 occurrences       and a maximum of 4 occurrences of the word “the” or the word “but” (upper or lower case).

[[Category:OSL640]]

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