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Tutorial9: Regular Expressions

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{{Admon/caution|DO NOT USE THIS VERSION OF THE LAB. This page will no longer be updated.|'''New version here:''' https://seneca-ictoer.github.io/ULI101/A-Tutorials/tutorial9 '''Andrew's students please go here:''' http://wiki.littlesvr.ca/wiki/OPS145_Lab_8}}

=USING REGULAR EXPRESSIONS=

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

|colspan="2" |~~Course Notes~~'''Slides:'''<ul><li>Week 9 Lecture 1 Notes: [https://~~ict~~wiki.cdot.senecacollege.ca/~~~murray~~uli101/slides/ULI101-9.1.pdf PDF] | [https://wiki.~~saul~~cdot.senecacollege.ca/uli101/slides/ULI101-~~Week9~~9.1.pptx PPTX]</li><li>Week 9 Lecture 2 Notes: [https://wiki.cdot.senecacollege.ca/uli101/slides/ULI101-9.2.pdf PDF] | [https://~~ict~~wiki.cdot.senecacollege.ca/~~~murray.saul~~uli101/~~uli101~~slides/ULI101-~~Week9~~9.2.pptx PPTX] </li></ul>

| style="padding-left:15px;" |'''Regular Expressions:'''

* [https://techterms.com/definition/regular_expression#:~:text=A%20regular%20expression%20(or%20%22regex,wildcards%2C%20and%20ranges%20of%20characters.&text=A%20regular%20expression%20can%20be,%2C%20such%20as%20%22app%22. Definition]

* [https://en.wikipedia.org/wiki/Regular_expression#:~:text=Regular%20expressions%20are%20used%20in,built%2Din%20or%20via%20libraries. Purpose (WIKI)]

| style="padding-left:15px;"|'''Linux Commands:'''

* [https://ss64.com/bash/egrep.html egrep]

* [https://www.man7.org/linux/man-pages/man1/man.1.html man]

* [https://linux.die.net/man/1/wget wget]

|colspan="1" style="padding-left:15px;" width="30%"|'''Brauer Instructional Videos:'''<ul><li>[https://www.youtube.com/watch?v=-2pwLHcvCsU&list=PLU1b1f-2Oe90TuYfifnWulINjMv_Wr16N&index=12 Using grep Command with Regular Expressions]</li></ul>

|}

= KEY CONCEPTS =

A '''regular expression''' … is a sequence of characters that define a search pattern. Usually such patterns are used by string searching algorithms for "find" or "find and replace" operations on strings, or for input validation. Reference: https://en.wikipedia.org/wiki/Regular_expression===Regular Expressions===

~~===Regular Expressions vs. Filename Expansion===~~ [[Image:re-1.png|thumb|right|350px|'''Filename expansion symbols''' allow the Linux shell to expand filenames as arguments (referred to as “globbing”).]] In a previous tutorial, you learned that '''filename expansion symbols''' allow the Linux shell to expand filenames as arguments (referred to as “globbing”) for file management commands. This is very useful for managing multiple files sharing similar characteristics such as the same file extension. ''Filename Expansion symbols'' are used to search, edit and manipulate text and are used with Linux file management commands such as '''ls''', '''rm''', '''mv''', '''cp''', '''cat''', '''less''', '''more''', '''head''', '''tail''', '''sort''', '''uniq''', '''cut''', '''tr''', and '''wc'''. ~~[[Image:re-2.png|thumb|right|250px|'''Concept''' of matching a simple pattern of text contained within a text file.]]~~A '''regular expression''' is a combination of two types of characters: '''literals''' and '''special characters'''. ~~In combination, these characters define a logical pattern.~~ Strings of text can be compared to this pattern~~ ~~to see if ~~they fit the pattern defined by the expression~~there is a match. ~~Reference: https://www.whoishostingthis.com/resources/regex/~~

This usually refers to text that is contained inside a '''file''' or text as a result of issuing Linux commands using a '''Linux pipeline command'''.

===Literal (Simple) Regular Expressions===

[[Image:re-3.png|thumb|right|200px|~~The simplest~~ A '''simple''' ('''literal''') regular expression is a series of letters and numbers~~, possibly including white space~~ (tabs or ~~space characters~~spaces).]]The simplest regular expression is a series of letters and numbers, ~~possibly including white space~~ (tabs or ~~space characters~~spaces)~~, that have no special meaning~~. ~~Such a~~ A '''simple''' ('''literal''') regular expression consists of ~~``literals''; that is,~~ normal ~~letters~~characters, which used to match ~~only an identical letter in the data being searched~~patterns. Although there are many Linux commands that use regular expressions, the '''grep ''' command is a useful command to learn how to display matches of patterns of strings within text files.

For example:

grep Linux document.txt

When an editor searches for a '''literal regular expression''', it can only score a ``hit'' if it finds exactly that sequence of characters in the data it is searching. Reference: http://osr507doc.xinuos.com/en/OSUserG/_Literal_chars_in_regexps.html

~~ ~~

===Complex / Extended Regular Expressions=== ~~The problem with using literals or simple regular expressions is that only simple or general patterns are matched.~~

'''Complex Regular Expressions''' ~~use symbols to help match text for more~~ The problem with just using '''simple''' ('''literal''') regular expressions is that only ~~precise~~simple ~~(complex) patterns.~~or general<br/u>~~The most common complex regular expression symbols~~ patterns are ~~displayed below:~~matched.

''Complex Regular Expressions'' use symbols to help match text for more precise (complex) patterns. The most common complex regular expression symbols are displayed below: :*'''Anchors: ''' ^ , $ Match lines the begin (^) or end ($) with a pattern.~~ ~~ :*'''Single Character:'''   . Represents a single character that can be any type of character.~~ ~~ :*'''Character Class:''' [ ] , [^ ] Represents a single character but with restrictions.~~ ~~ :*'''Zero or More Occurrence:''' * Zero or more occurrences of previous character.

'''Extended Regular Expressions'''

''Extended Regular Expressions'' consist of additional special characters to “extend” the capability of regular expressions. You must use the '''egrep''' or '''grep -E''' commands in order to properly use extended regular expressions.

:'''Repetition:''' {min,max} Allows for more precise repetitions. Using braces, you can specify the '''minimum''' and/or '''maximum''' number of repetitions.

~~===Extended Regular Expressions===~~ :'''~~Extended Regular Expressions~~Groups:''' ~~consist of additional special characters~~( ) Allows you to ~~“extend” the capability~~ search for repetition for a '''group of ~~regular expressions. You must use the~~ characters''', a '''~~egrep~~word''' , or a '''~~grep -E~~phase''' ~~commands~~. ~~in order~~ You enclose them within brackets ( ) to ~~properly use extended regular expressions with the grep command~~specify a '''group'''.

:'''or Condition:''' | Can be used with '''groups''' to match a variety of character(s), words or phases. The | symbol is used to separate the variety of character(s) within a ''group''.

:*Examples of how to use '''~~Repetition: {min,max}~~extended regular expressions'''~~ Allows for more precise repetitions. Using braces, you can specify ~~with the '''~~minimum~~egrep''' ~~and/or '''maximum''' number of repetitions.~~command are displayed below:

=INVESTIGATION 1:*'''or Condition: |''' Can be used with grouping to match a variety of character(s), words or phases. The | symbol is used to separate the variety of character(s) within a group. SIMPLE & COMPLEX REGULAR EXPRESSIONS=

~~Examples of how to use these complex regular expressions with the '''egrep''' command are displayed below: ~~ <~~table align~~span style="~~left"><tr valign="top~~color:red;">~~<td>[[Image:re-8.png|thumb|right|280px|Example of using~~ '''~~repetition~~ATTENTION'''~~.]]</td><td>[[Image~~:~~re-9.png|thumb|right|250px|Example of using~~ This online tutorial will be required to be completed by '''~~grouping~~Friday in week 10 by midnight'''~~.]]</td><td>[[Image:re-10.png|thumb|right|250px|Example~~ to obtain a grade of ~~using~~ '''~~or condition with grouping~~2%'''~~.]]~~towards this course</tdspan>~~</tr></table>~~ ~~ ~~ ~~=INVESTIGATION 1: SIMPLE & COMPLEX REGULAR EXPRESSIONS=~~

~~ ~~In this ~~section~~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~~ # Issue the following linux Linux command to '''~~wget~~copy''' ~~command is used to download files from the Internet to your shell. This will be useful~~ a text file to ~~download~~ ''your'~~text files~~''' ~~and~~ 'home''~~data files~~'~~'' that we will be using for this tutorial. # Issue~~ directory from the ~~following linux Linux command to download a text file to your~~ ULI101 home directory: ~~wget <nowiki>https://ict.senecacollege.ca/~~cp ~~~murray.saul~~uli101/~~uli101~~tutorialfiles/textfile1.txt<~/~~nowiki>~~~~ # Issue the '''ls''' Linux command to confirm that the text file was downloaded.~~ # View the contents of the '''textfile1.txt''' file using the '''more''' command ~~and quickly view the contents of~~ see what data is contained in this file. Although there are several Linux commands that use regular expressions, we will ~~only~~ 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 ~~pattern~~patterns. # ~~Now, issue~~ Issue the grep Linux command with the -i option to ignore case sensitively: grep -i "the" textfile1.txt What do you notice is different when issuing this command? You will notice that the pattern "'''the'''" is matched including larger words like "'''them'''" and "'''their'''". You can issue the '''grep''' command with the -w option to only match the pattern as a '''word'''. # Issue the following Linux command: grep -w -i "the" textfile1.txt You should now see only strings of text that match the word '''"the"''' (upper or lower case). Matching literal or simple regular expressions can be useful, but are '''limited''' in what pattens they can ~~assist with pattern matching~~match. For example, you may want to search for a pattern located at the '''beginning''' or '''end''' of the string. There are other regular expression symbols that provide more '''precise''' search pattern ~~matches~~matching. These special characters are known as '''complex''' and '''extended''' regular expressions symbols. In For the remainder of this ~~section~~investigation, we will focus on ~~complex~~ '''complex regular expressions''' and then ~~discuss~~ focus on ''extended regular expressions'' in INVESTIGATION 2. <table align="right"><tr valign="top"><td>[[Image:regexps-2.png|thumb|right|280px|Anchoring regular expressions at the '''beginning''' of text.]]</td><td>[[Image:regexps-3.png|thumb|right|250px|Anchoring regular expressions at the '''ending''' of text.]]</td></tr></table># Issue the following Linux command: grep -w -i "^the" textfile1.txt The '''^''' symbol is referred to as an '''anchor'''. In this case, it only matches the word "'''the'''" (both upper or lowercase) at the beginning of the string.

# Issue the following Linux command: grep -w -i "the$" textfile1.txt The '''$''' symbol is used to anchor patterns at the end of the string.

# Issue the following Linux command to anchor the word "'''the'''" '''simultaneously ''' at the beginning and end of the string: grep -w -i "^the$" textfile1.txt What do you notice? Anchoring patterns at both the beginning and ending of strings can greatly assist for more '''precise''' search ~~patterns~~pattern matching. We will now be demonstrate the ~~power~~ '''effectiveness''' of ~~anchoring~~combining ~~combined~~ '''anchors''' with other complex regular expressions symbols. <table align="right"><tr valign="top"><td>[[Image:regexps-4.png|thumb|right|280px|Anchoring regular expressions using '''period''' symbols at the '''beginning''' of text.]]</td><td>[[Image:regexps-5.png|thumb|right|250px|Anchoring regular expressions using '''period''' symbols simultaneously at the '''beginning''' and '''ending''' of text.]]</td></tr></table># Issue the following Linux command to match strings that '''begin with 3 characters''': grep "^..." textfile1.txt What do you notice? Can lines that contain '''less than 3 characters''' be displayed? # Issue the following Linux command to match strings that '''begin and end with 3 characters''': grep "^...$" textfile1.txt What do you notice compared to the previous command? # Issue the following Linux command to match strings that '''begin with 3 digits''': grep "^[0-9][0-9][0-9]" textfile1.txt What did you notice? # Issue the following Linux command to match strings that '''end with 3 uppercase letters''': grep "[A-Z][A-Z][A-Z]$" textfile1.txt ~~Did any lines~~ <table align="right"><tr valign="top"><td>[[Image:regexps-6.png|thumb|right|220px|Anchoring '''3 digits''' at the '''beginning''' and '''ending''' of text.]]</td><td>[[Image:regexps-7.png|thumb|right|250px|Anchoring '''3 alpha-numeric characters''' at the '''beginning''' and '''ending''' of text.]]</td></tr></table>What type of strings match this pattern? # Issue the following Linux command to match strings that '''consist of only 3 digits''': grep "^[0-9][0-9][0-9]$" textfile1.txt What did you notice? # Issue the following Linux command to match strings that '''consist of only 3 alphanumeric digits''': grep "^[a-zA-Z0-9][a-zA-Z0-9][a-zA-Z0-9]$" textfile1.txt What did you notice? The "*" complex regular expression symbol is often confused with the "*" '''filename expansion ''' symbol. In other words, it does NOT represent zero or more of '''any character''', but zero or more '''occurrences''' of the character that comes '''before''' the "*" symbol. # To demonstrate, issue the following Linux command to display '''zero or more occurrences ''' of the letter "'''x'''": grep "x*" textfile1.txt You will most likely notice most lines of the file is displayed. # Let's issue a Linux command to display strings that contain '''more than one occurrence ''' of the letter "'''x'''": grep "xx*" textfile1.txt Why did this work? because the pattern indicates one occurrence of the letter "x", followed by '''zero or MORE occurrences''' of the next letter "x". If you combine the complex regular expression symbols ".*" it will act like zero or more occurrences of any character (i.e. like "*" did in filename expansion).

# Issue the following Linux command to match strings begin and end with a number with nothing or anything inbetween: grep "^[0-9].*[0-9]$" textfile1.txt Using '''simultaneous anchors''' combined with the ".*" symbol(s) can help you to refine your search patterns of strings.

# Issue the following Linux command to display strings that begin with a capital letter, end with a number, and contains a capital X somewhere inbetween: grep "^[A-Z].*X.*[0-9]$" textfile1.txt Let's look at another series of examples involving searching for strings that only contain '''valid numbers'''. 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 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~~uli101/~~uli101~~tutorialfiles/numbers1.dat<~/~~nowiki>~~regexps

# 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 whole numbers: grep "^[0-9][0-9]*$" numbers1.dat | tee whole.txt You should see that this now works.

# Issue the following Linux pipeline command to display ~~whole positive or negative~~ only '''signed''' integers: grep "^[+-][0-9][0-9]*$" numbers1.dat | tee signed.txt What did you notice?Positive and negative numbers display, not '''unsigned''' numbers. [[Image:regexps-8.png|thumb|right|300px|Simultaneous '''anchoring''' of regular expressions using '''character class''' and '''zero or more occurrences''' to display '''signed''' and '''unsigned''' integers.]]# Issue the following Linux pipeline command to display ~~only whole numbers (with~~ '''signed''' or ~~without a positive or negative sign)~~'''unsigned integers''': grep "^[+-]*[0-9][0-9]*$" numbers1.dat | tee all.txt Did this command work? # Issue the following command to check that you created those hard links: ~~bash /home/murray.saul/scripts~~~uli101/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? : Although very useful, '''complex''' regular expressions do NOT entirely solve our problem of displaying '''valid''' unsigned and signed numbers (not to mention displaying decimal numbers). In the next investigation, you will learn how to use '''extended''' regular expressions that will completely solve this issue.

:~~Proceed~~ You can proceed to INVESTIGATION 2.

=INVESTIGATION 2: EXTENDED REGULAR EXPRESSIONS =

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

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

# Issue the following ~~linux pipeline~~ Linux command to ~~download~~ copy another data file called '''numbers2.dat''': ~~wget <nowiki>https://ict.senecacollege.ca/~~cp ~~~murray.saul~~uli101/~~uli101~~tutorialfiles/numbers2.dat<~/~~nowiki>~~ # 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 ~~more~~ ''invalid '' numbers contained in this file. When finished, exit the more command. ~~# Issue~~ [[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 pipeline~~ Linux command to display ~~only whole numbers (with~~ '''signed''' or ~~without a positive or negative sign)~~'''unsigned integers''': grep "^[+-]*[0-9][0-9]*$" numbers2.dat You should notice '''multiple''' '''+''' or '''-''' '''signs''' appear prior to some numbers. This occurs since you are searching or one or MORE occurrences of a + or - sign. Using '''extended regular expression''' symbols to specify '''minimum''' and '''maximum''' repetitions: '''{min,max}''' can solve that problem. # Issue the following ~~linux pipeline~~ Linux command (using extended regular expression symbols) to display ~~only whole numbers (with~~ '''signed''' or ~~without a positive or negative sign)~~'''unsigned integers''': grep "^[+-]{0.,1}[0-9]{1,}$" numbers2.dat '''NOTE:No output will be displayed! Why?''' ~~most likely, there were '''NO results'''.~~ 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 ~~more simply)~~ 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. ~~# Reissue the above pipeline command using~~ We will use '''~~egrep~~pipeline commands''' ~~instead~~ to both display stdout to the screen and save to files for confirmation of running these pipeline commands when run a ''~~grep~~'checking-script''':later in this investigation. <~~span style="color:blue;font-weight:bold;font-family:courier;"~~br># Issue the following Linux pipeline command using '''egrep''' instead of ''grep'': egrep "^[+-]{0,1}[0-9]{1,}$" numbers2.dat | tee better-number1.txt ~~You should have noticed that the command worked correctly this time because you used the~~ [[Image:eregexps-2.png|thumb|right|300px|Using '''~~egrep~~extended''' ~~command. ~~regular expression symbols (such as '''~~NOTE:~~repetition''' ~~In extended regular expressions, the~~ ) to refine matches of ''signed'?'and '' ~~symbol can be used to represent the~~ unsigned''~~'{0,1}~~integers.]]You should have noticed that the command worked correctly this time because you used the '''egrep''' ~~repetition symbols~~command. ~~and the~~ '''+NOTE:''' With extended regular expressions, the '''?''' symbol can be used to represent the '''{0,1,}''' repetition symbols~~ # Reissue~~ and the ~~above pipeline command using~~ '''~~egrep~~+''' ~~instead of~~ symbol can be used to represent the '''{1,}'~~grep~~'':repetition symbols <~~span style="color:blue;~~br># Issue the following Linux pipeline command using the repetition shortcuts ~~egrep~~ "^[+~~-]?[0-9]+$~~" ~~numbers2.dat | tee better~~ and "?": <brspan style="color:blue;font-weight:bold;font-family:courier;">~~You should have seen the same results, but the extended regular expression required less typing~~egrep "^[+-]?[0-9]+$" numbers2.dat | tee better-number2.txt ~~# Issue the following linux pipeline command to display signed, unsigned, whole, and decimal numbers: ~~egrep "^[+-]{0,1}[0-9]{1~~# Issue the following Linux pipeline command to display '''signed''',~~}[.]{0~~'''unsigned''',~~1}[0-9]*$" numbers2.dat | tee better-number3.txt~~'''whole''', and '''decimal''' numbers: <~~br># Issue the following Linux command to check that you correctly issued<br~~span style="color:blue;font-weight:bold;font-family:courier;">egrep "^[+-]{0,1}[0-9]{1,}[.]{0,1}[0-9]*$" numbers2.dat | tee better-number3.txt~~those ''Linux pipeline commands'' using the '''tee''' command to create those text files:~~ <~~span style="color:blue;font-weight:bold;font-family:courier;"~~br>~~bash /home/murray.saul/scripts/week9-check-2~~Were all signed and unsigned intergers and decimal numbers displayed?<~~/span~~br> # Issue the follwoing command to check that you correctly issued ~~If you encounter errors, then view the feedback to make corrections, and then re-run the checking script.~~those ''Linux pipeline commands'': ~~If you receive a congratulation message that there are no errors, then proceed with this tutorial.<br~~~uli101/week9-check-2<br/span>~~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~~ If you encounter errors, then view the feedback to ~~just a single character or a GROUP of numbers as opposed to a single digit~~make corrections, and then re-run the checking script. ~~ # Issue the following linux pipeline command to download another data file called '''words~~If you receive a congratulation message that there are no errors, then proceed with this tutorial.~~dat~~ You can also use extended regular expression symbols for '''grouping':''. For example, you can search for repetitions of GROUPS of characters (like a word)<~~span style="color:blue;font-weight:bold;font-family:courier;">wget <nowiki~~br>~~https://ict.senecacollege.ca/~murray~~as opposed to just a single character or a GROUP of numbers as opposed to a single digit.~~saul/uli101/words.dat~~<~~/nowiki><br~~br> # ~~View the contents of~~ Issue the following linux pipeline command to copy another data file called '''~~numbers2~~words.dat''' ~~file using the '''more''' command and quickly view the contents of this file.~~: <~~br>You should notice valid and more invalid numbers contained in this file. When finished, exit the more command~~span style="color:blue;font-weight:bold;font-family:courier;">cp ~uli101/tutorialfiles/words.dat ~/ # ~~Issue~~ View the ~~following linux pipeline command to display two or more occurrences~~ contents of the ~~word "the":~~'''words.dat''' file using the '''more''' command and quickly view the contents of this file. ~~egrep -i "(the){2~~Within this file,}" you should notice some lines that contain repetitions of words.~~dat | tee word-search1~~When finished, exit the more command.~~txt more~~ # Issue the following linux pipeline command to display '''~~'NOTE:~~two or more occurrences''' ~~You should NOT see any output due to~~ of the word "the ~~fact that a~~ ":<ubr>~~space~~<~~/u> should be included at the end of the word~~ span style="~~'''~~color:blue;font-weight:bold;font-family:courier;">egrep -i "(the~~'''~~){2,}"words.dat | tee word-search1.txt more ~~Usually words are separated by spaces; therefore, there were no matches since there were not occurrences~~ ~~of "thethe" as opposed to "~~'''~~the the~~NOTE: No output is displayed! Why?'''~~" (i.e. no space after repetition of the pattern).~~ ~~# Reissue~~ This is due to the ~~previous pipeline command including~~ fact that a space ~~in brackets:~~<br/u>~~~~egrep -i "(the ){2~~Usually words are separated by spaces; therefore,~~}" words.dat | tee word-search2.txt~~there were no matches since there were not occurrences ~~ The~~ of "thethe" as opposed to "|'''the the'''" (ori.e. no space after repetition of the pattern) ~~symbol 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~~ Reissue the ~~following linux~~ previous pipeline command ~~to search for 2 or more occurrences of~~ with the word "the followed by a '''~~the~~space'''" within the brackets:<~~u>or the word "'''and'''":<br~~br>egrep -i "(the ~~|and~~ ){2,}" words.dat | tee word-~~search3~~search2.txt ~~# Issue the following Linux command to check that you correctly issued those~~ [[Image:eregexps-3.png|thumb|right|330px|Using ''~~Linux pipeline commands~~'extended' ~~using the~~ ''regular expression symbols (such as '~~tee~~''grouping''' ~~command~~ ) to ~~create those text files: ~~bash~~ "|"</~~home/murray.saul/scripts/week9-check-3 <br~~span> (or) symbol (same symbol as "pipe") can be used within the grouping symbols to allow matching of additional groups of characters. ~~If you encounter errors~~Again, ~~then view~~ it is important to follow the ~~feedback to make corrections, and then~~ 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: ~uli101/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~~ -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 ~~tutorial~~course.~~ 

:~~Proceed~~ You can proceed to INVESTIGATION 3

=INVESTIGATION 3: OTHER COMMANDS ~~THAT USE~~ USING REGULAR EXPRESSIONS = In this ~~section~~investigation, you will see ~~how regular expressions can be used with other Linux utilities~~ 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~~ Linux commands contain the regular expressions within quotes,~~ ~~but '''most ''' other Linux commands specify regular expressions using ~~forward slashes~~ '''forward slashes''' (e.g. ~~'''~~/regular expression</~~'''~~ span>   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 '''~~more~~less''' command. # Issue the following ~~linux~~ Linux command to ~~view the contents of the~~ copy another data file called '''~~textfile1~~large-file.txt''' ~~(downloaded in a previous section)~~: ~~more textfile1~~cp ~uli101/tutorialfiles/large-file.txt~/ ~~#We want to search for a pattern~~ [[Image:other-re-2.png|thumb|right|300px|Entering '''/uli101''' in the '''less''' command can display all matches of "'''uli101''' ~~within this~~ " throughout the text file.~~ Type~~ ]]# Issue the following ~~regular expression and press ENTER~~Linux command to view the contents of the '''large-file.txt''': ~~/uli101~~less large-file.txt~~ What did you notice?~~ #~~Search~~ We want to search for ~~the next occurrence of the~~ a pattern '''uli101''' ~~by '''re-typing'''~~within this text file. Type the following regular expression and ~~pressing~~ press ENTER: /uli101 ~~you~~ You should ~~now~~ see the ~~'''second occurrence''' of this~~ pattern ~~within~~ "uli101" throughout the text file. # Press the letter q to exit the '''~~more~~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'''".]]Let's learn how to perform a simple '''search and replace''' within the '''vi''' utility by using regular expressions. # Issue the following ~~linux~~ Linux command to edit the '''~~textfile1~~large-file.txt''' file: vi ~~textfile1~~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''': /uli101 You should ~~move to the '''first occurrence''' of~~ notice the pattern: "'''uli101'''" highlighted for ALL occurrences in this text file. Let's '''search ''' for the '''uli101''' pattern, ~~but~~ and '''replace ''' it in capitals (i.e '''ULI101'''). In vi, ~~in order~~ to ~~perform and~~ issue a command, you need to ~~go into last line mode, and~~ enter '''LAST LINE''' MODE then issue a command ~~to apply to the entire text file, followed by~~ . Let's issue a ~~regular expression~~ command from '''LAST LINE''' MODE to search ~~for~~ and ~~a regular expression~~ replace '''uli101''' to ~~replace (i.e.~~ '''~~/search/replace/~~ULI101'''). [[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'''.]]# ~~Type~~ Making certain that you are '''COMMAND''' MODE in vi, type the following and press '''ENTER''': :%s/uli101/ULI101/g ~~You should have noticed that the first occurrence of uli101 has been changed to ULI101. # Navigate throughout the text file to see if the other occurrences have been replaced. You should notice they haven~~'~~t for~~ ''NOTE:''' The letter '''g''' after the ~~other two occurrences. In order to~~ replace ~~for ALL occurrences, you need to add the letter g (meaning~~ regular expression represents "'''global'''"~~) at the end~~ and will replace ALL occurrences of uli101 in the ~~last forward slash~~ text document (~~e.g /'''search/replace/g'''~~as opposed to replacing the first occurrence for every line). # ~~Making certain that you are command mode in vi, type~~ Type the following (in uppercase letters) and press '''ENTER''': ~~:%s/uli101~~/ULI101/g You should notice the pattern "'''ULI101'''" highlighted for ALL occurrences in this text file. # Navigate throughout the text file to confirm that ALL occurrences of '''uli101 ''' have been replaced with '''ULI101'''.

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

~~: After you complete the Review Questions sections to get additional practice, then work on your '''online assignment 3'''.~~

~~ ~~

= LINUX PRACTICE QUESTIONS =

simulate a quiz:

https://~~ict~~wiki.cdot.senecacollege.ca/~~~murray.saul~~uli101/~~uli101~~files/uli101_command_practice_9a.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).

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

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

<pre>

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

1. grep plym ~~~murray.saul/~~uli101/cars 2. grep -i fury ~~~murray.saul/~~uli101/cars 3. grep “^[m-z]” ~~~murray.saul/~~uli101/cars 4. grep -i “^[m-z]” ~~~murray.saul/~~uli101/cars 5. grep “3$” ~~~murray.saul/~~uli101/cars 6. grep -i “c.*5$” ~~~murray.saul/~~uli101/cars

simulate a quiz:

https://~~ict~~wiki.cdot.senecacollege.ca/~~~murray.saul~~uli101/~~uli101~~files/uli101_command_practice_9b.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).

'''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>

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

1. grep "^[-+]" ~~~murray.saul/~~uli101/numbers.txt 2. grep "^[-+]*.[0-9]" ~~~murray.saul/~~uli101/numbers.txt 3. grep "^[+-]?[0-9]" ~~~murray.saul/~~uli101/numbers.txt    (Why?) 4. egrep "^[+-]?[0-9]" ~~~murray.saul/~~uli101/numbers.txt 5. egrep "^[+-]?[0-9]+$" ~~~murray.saul/~~uli101/numbers.txt 6. egrep "^[+-]?[0-9]+[.]?[0-9]+$" ~~~murray.saul/~~uli101/numbers.txt

_________________________________________________________________________________ Author: Murray Saul License: LGPL version 3Link: https://www.gnu.org/licenses/lgpl.html _________________________________________________________________________________

[[Category:ULI101]]

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