Changes

:* Explain Define the purpose of term '''Regular Expressions'''

:* List various several Linux commands that can use regular expressions<br>

|colspan="2" |Course Notes'''Slides:'''<ul><li>Week 9 Lecture 1 Notes:<br>[https://ictwiki.cdot.senecacollege.ca/~murrayuli101/slides/ULI101-9.1.pdf PDF] | [https://wiki.saulcdot.senecacollege.ca/uli101/slides/ULI101-Week99.1.pptx PPTX]</li><li>Week 9 Lecture 2 Notes:<br> [https://wiki.cdot.senecacollege.ca/uli101/slides/ULI101-9.2.pdf PDF] | [https://ictwiki.cdot.senecacollege.ca/~murray.saululi101/uli101slides/ULI101-Week99.2.pptx PPTX]<br></li></ul>

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

| style="padding-left:15px;"|'''Linux Commands :'''* [https://ss64.com/bash/egrep.html egrep]

|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>

Usually such patterns are used by string searching algorithms for "find" or "find and replace" operations on strings, or for input validation. </i>A '''regular expression''' is a combination of two types of characters: '''literals''' and '''special characters'''.<br>Reference: https://enStrings of text can be compared to this pattern to see if there is a match.wikipedia.org</wiki/Regular_expressioni>

===Regular Expressions vs. Filename Expansion=== <table align="right"><tr valign="top"><td>[[Image:re-1.png|thumb|right|350px|'''Filename expansion symbols''' allow the Linux shell This usually refers to expand filenames as arguments (referred to as “globbing”).]]</td>text that is <tdu>[[Image:re-2.png|thumb|right|250px|'''Concept''' of matching a simple pattern of text contained within a text file.]]</td></tableu>In inside a previous lesson, 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''' and '''more'''. This can represent text contained in files or text as a result <br>of issuing Linux commands using a pipeline. <i>A '''regular expression''' is a combination of two types of characters: '''literals''' and '''special charactersLinux pipeline command'''.<br>In combination, these characters define a logical pattern. Strings of text can be compared to this pattern<br>to see if they fit the pattern defined by the expression.</i> Reference: https://www.whoishostingthis.com/resources/regex/

[[Image:re-3.png|thumb|right|250px200px|The simplest A '''simple''' ('''literal''') regular expression is a series of letters and numbers, possibly including white space (tabs or space charactersspaces).]]The simplest regular expression is a series of letters and numbers, possibly including white space (tabs or space charactersspaces), that have no special meaning. Such a <br>A '''simple''' ('''literal''') regular expression consists of ``literals''; that is, normal letterscharacters, which used to match only an identical letter in the data being searchedpatterns.<br><br>For example:"This is a Although there are many Linux commands that use regular expression"<br><br><i>When an editor searches for a expressions, the '''literal regular expressiongrep''', it can only score command is a ``hit'' if it finds exactly that sequence useful command to learn how to display matches of patterns of characters in the data it is searchingstrings within text files.</ibr> <br>ReferenceFor example:<span style="color:blue;font-weight: httpbold;font-family://osr507doccourier;">grep Linux document.xinuos.comtxt</en/OSUserG/_Literal_chars_in_regexps.htmlspan><br><br>

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

For example, the pattern “'''theComplex Regular Expressions'''” would be matched for larger word containing that pattern like <br><br>The problem with just using '''theresimple''', ('''theyliteral''', '''either''', '''them''', '''their''', etc.) regular expressions is that only <u>simple<br/u>Another problem is that you may want to search for pattern at a specific location within the string of text (like at the beginning or end)<u>general</u> patterns are matched.

There are other regular expression tools to provide more precise matches. These tools are '''complex''' and '''extended''' regular expressions.  '''Complex Regular Expressions''' use symbols to help match text for more <u>precise</u> (complex) patterns.<br>The most common complex regular expression symbols are displayed below:<br><br>:*'''Anchors: ''' '''<span style="color:blue;font-family:courier;font-weight:bold;">^''' </span> , '''<span style="color:blue;font-family:courier;font-weight:bold;">$</span><br>Match lines the begin (^) or end ($) with a pattern.<br>:'''Single Character:*'''Characters &nbsp; <span style="color:blue;font-family:courier;font-weight:bold;">.</span><br>Represents a single character that can be any type of character.'''<br>:*'''Character Class [ ]:''' <span style="color:blue;font-family:courier;font-weight:bold;">[ ]</span> , '''<span style="color:blue;font-family:courier;font-weight:bold;">[^ ]'''</span><br>Represents a single character but with restrictions.<br>:*'''Zero or More Occurrence *:''' <span style="color:blue;font-family:courier;font-weight:bold;">*</span><br>Zero or more occurrences of previous character.<br><br>

:Examples of how to use these '''complex regular expressions with the grep command ''' are displayed below:

<table align="left"><tr valign="top"><td>[[Image:re-4.png|thumb|right|220px200px|Example of using '''anchors'''.]]</td><td>[[Image:re-5.png|thumb|right|200px175px|Example of matching by '''character(s)'''.]]</td><td>[[Image:re-6.png|thumb|right|220px|Example of using '''character class'''.]]</td><td>[[Image:re-7.png|thumb|right|200px|Example of matching '''zero or more occurrence of preceding character'''.]]</td></tr></table><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br>

'''Extended Regular Expressions''' consist of additional special characters the “extend” the capability of regular expressions.

:'''Grouping ( )Groups:'''<span style="color:blue;font-family:courier;font-weight:bold;">( )</span><br>Perhaps Allows you want to search for repetition for a '''group of characters''', a '''word''', or a '''phase'''.<br>You can enclose them within brackets <span style="font-family:courier;font-weight:bold;">( ) </span> to specify a '''group'''.

:Examples of how to use '''extended regular expressions'''or Condition |with the '''egrep''' command are displayed below:<br><br>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).

Examples <table align="left"><tr valign="top"><td>[[Image:re-8.png|thumb|right|280px|Example of using '''repetition'''.]]</td><td>[[Image:re-9.png|thumb|right|250px|Example of using '''groups'''.]]</td><td>[[Image:re-10.png|thumb|right|250px|Example of how to use these complex regular expressions using '''or''' condition with the grep command are displayed below:'''groups'''.]]</td></tr></table><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br>

<table align="left"><tr valignINVESTIGATION 1: SIMPLE &amp; COMPLEX REGULAR EXPRESSIONS="top"><td>[[Image:re-8.png|thumb|right|280px|Example of using '''repetition'''.]]</td><td>[[Image:re-9.png|thumb|right|250px|Example of using '''grouping'''.]]</td><td>[[Image:re-10.png|thumb|right|250px|Example of using '''or condition with grouping'''.]]</td></tr></table><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br>

<span style=INVESTIGATION 1"color: SIMPLE &ampred; COMPLEX REGULAR EXPRESSIONS=">'''ATTENTION''': This online tutorial will be required to be completed by '''Friday in week 10 by midnight''' to obtain a grade of '''2%''' towards this course</span><br><br>

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

# Issue a Linux command to '''confirm''' you are located in your '''home ''' directory.<br><br>The # Issue the following linux Linux command to '''wgetcopy''' command is used to download files from the Internet a text file to ''your shell.'' '''home''' directory from the ULI101 home directory:<br>This will be useful to download text files that we will be using for this tutorial.<br><br># Issue the following linux command ('''copy and paste''' to save time):<br><span stylespan style="color:blue;font-weight:bold;font-family:courier;">wget <nowiki>https://ict.senecacollege.ca/~murray.saulcp ~uli101/uli101tutorialfiles/textfile1.txt<~/nowiki></span><br><br># Issue View the contents of the '''lstextfile1.txt''' command to confirm that file using the text file was downloaded'''more''' command see what data is contained in this file.<br><br># View the contents of Although there are several Linux commands that use regular expressions,<br>we will be using the '''textfile1.txtgrep''' file using the command for this investigation.<br><br>[[Image:regexps-1.png|thumb|right|250px|Output of '''moregrep''' command and quickly view matching simple regular expression "'''the contents of this file'''" (only lowercase). When finished, Notice the pattern matches larger words like "'''exittheir''' the more command.<br><br>Although there are several Linux commands that use regular expressions, we will only be using the " or "'''grepthem''' command for this section.<br><br>".]]#Issue the following linux pipeline Linux command to match the pattern '''the ''' within '''textfile1.txt''':<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "the" textfile1.txt | more</span><br><br># Now, issue Take a few moments to view the grep linux pipeline command with output and observe the '''-i''' option to ignore case sensitively:matched patterns.<br><span br># Issue the grep Linux command with the <span style="color:blue;font-weight:bold;font-family:courier;">grep -i "the" textfile1.txt | more</span>option to ignore case sensitively:<br><br>What do you notice is different with this pipeline command?<brspan style="color:blue;font-weight:bold;font-family:courier;"><grep -i "the" textfile1.txt</span><br><br>What do you notice is different when issuing this command?<br><br>You will notice that the pattern "the'''the'''" is matched including larger words that contain the pattern like "'''them'''" and "the'''their'''". <br>You can use issue the -w option '''grep''' command with the grep command in order to just match only words for a pattern.<br><br># Issue the following linux pipeline command:<br><span style="color:blue;fontspan style="font-weight:bold;font-family:courier;">grep -w -i "the" textfile1.txt | more</span><br><br>You should now see </span> option to only strings of text that match the word pattern as a '''"the"word'''.<br><br>Matching literal or simple regular expressions can be useful, but are limited in what they can assist with pattern matching.# Issue the following Linux command:<br>For Example, you may want to search for pattern at a specific location within the string of text (like at <span style="color:blue;font-weight:bold;font-family:courier;">grep -w -i "the beginning or end of the string)" textfile1.txt</span><br><br>There are other regular expression tools to provide more precise matches. These tools are You should now see only strings of text that match the word '''complexthe''' and '''extended(upper or lower case).<br><br>Matching literal or simple regular expressions can be useful, but are '''limited''' regular expressions. We will now look at complex regular expression symbols now, and we will discuss ''extended regular expressions''''''Italic text'''' in the next section of this tutorial.<br>in what pattens they can match. For example, you may want to<br># Issue search for a pattern located at the following Linux pipeline command:<'''beginning''' or '''end''' of the string.<br><span style="color:blue;font-weight:bold;font-family:courier;"br>There are other regular expression symbols that provide more '''precise''' search pattern matching.<br>grep -w -i "^the" textfile1.txt | more</span><br><br>The These special characters are known as '''complex'''^and ''' symbol is an anchorextended''' regular expressions symbols. In this case, it only matches the <ubr>word</ubr> "For the" (both upper or lowercase) at the beginning of strings.<br>The remainder of this investigation, we will focus on '''$complex regular expressions''' symbol is used to anchor patterns at the end of strings.and then<br>focus on ''extended regular expressions'' in INVESTIGATION 2.<br># Issue the following Linux pipeline command:<br><span styletable align="right"><tr valign="colortop"><td>[[Image:blue;font-weight:bold;font-family:courier;">grep -w -i "the$" textfile1regexps-2.txt png|thumb|right|280px| more<Anchoring regular expressions at the '''beginning''' of text.]]</spantd><brtd>[[Image:regexps-3.png|thumb|right|250px|Anchoring regular expressions at the '''ending''' of text.]]</td><br>What do you notice?<br/tr><br/table># Issue the following Linux pipeline command to anchor the work "the" simultaneously at the beginning and the end of the string::<br><span style="color:blue;font-weight:bold;font-family:courier;">grep -w -i "^the$" textfile1.txt | more</span><br><br>What do you notice?The '''^''' symbol is referred to as an '''anchor'''.<br>In this case, it only matches<br>Anchoring patterns at both the word "'''the'''" (both upper or lowercase) at the <u>beginning</u> and <u>endingbeginning</u> of strings can greatly assist for more robust search patterns.<br>We will now be demonstrating '''simultaneous anchoring''' with other complex regular expressions symbolsthe string.<br><br># Issue the following Linux command to match strings that begin with 3 characters:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^...-w -i "the$" textfile1.txt | more</span><br><br>What do you notice?<br><brThe '''$''' symbol is used to anchor patterns at the <u>end</u> of the string.<br><br># Issue the following Linux command to match strings that begin and end with 3 characters:anchor the <u>word</u> "'''the'''"<br>'''simultaneously''' at the <span u>beginning</u> and <u>end</u> of the string:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep -w -i "^...the$" textfile1.txt | more</span><br><br>What do you notice?<br><br># Issue Anchoring patterns at both the following command to match strings that begin with 3 digits:<bru>beginning</u>and <span style="color:blue;font-weight:bold;font-family:courier;">grep "^[0-9][0-9][0-9]" textfile1.txt | more</spanu>ending</u>of strings can greatly assist<br><br># Issue the following command to match strings that end with 3 uppercase letters:for more '''precise''' search pattern matching.<br><span style="color:blue;font-weight:bold;font-family:courier;"br>We will now be demonstrate the '''effectiveness''' of <u>grep "[A-Z][A-Z][A-Z]$" textfile1.txt | more</spancombining</u><br><br'''anchors''' with <u># Issue the following command to match strings that consist of only 3 digits:other<br/u>complex regular expressions symbols.<span stylebr><br><table align="color:blue;font-weight:bold;font-family:courier;right">grep <tr valign="top"^><td>[0-9][0-9][0Image:regexps-9]$" textfile14.txt png|thumb|right|280px| more</span><br><br>The Anchoring regular expressions using '''period'*''symbols at the ' complex regular expression symbol is often confused with filename expansion. In other words, it does NOT represent zero or more of '''any characterbeginning''', but zero or or occurrences of the character that comes before the * symboltext.]]<br/td><brtd># To demonstration, issue [[Image:regexps-5.png|thumb|right|250px|Anchoring regular expressions using '''period''' symbols simultaneously at the following command to display zero or more occurrences '''beginning''' and '''ending''' of the letter x:text.]]</td><br/tr><span style="color:/table># Issue the following Linux command to match strings that '''begin with 3 characters''':<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "x*^..." textfile1.txt | more</span><br><br>You will most likely What do you notice most ? Can lines of the file is that contain '''less than 3 characters''' be displayed.?<br><br># Let's issue a Issue the following Linux command to display match strings that contain more than one occurrence of the letter x:'''begin <bru>and<span /u> end with 3 characters''':<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "xx*^...$" textfile1.txt | more</span><br><br>Why did this workWhat do you notice compared to the previous command? because the pattern indicates one occurrence of the letter x, followed by zero or MORE occurrences of the letter x.<br><br>If you combine # Issue the complex regular expression symbols .* it will act like zero or more occurrence of any character (like * did in filename expansion).following Linux command to match strings that '''begin with 3 digits''':<br><br># Issue the following command to match strings begin and end with a number with nothing or anything inbetween:<br><span style="color:blue;font-weightspan style="color:blue;font-weight:bold;font-family:courier;">grep "^[0-9].*[0-9]$[0-9]" textfile1.txt | more</span><br><br>Using What did you notice?<br><br># Issue the following Linux command to match strings that '''simultaneous anchorsend with 3 uppercase letters''' combined with the .* symbol(s) can help you to refine your search patterns of strings.:<br><br># Issue the following linux pipeline command to display strings that begin with a capital letter, ends with a number, and contains a capital X somewhere inbetweenspan style="color:<br><span style="color:blue;blue;font-weight:bold;font-family:courier;">grep "^[A-Z].*X.*[0A-Z][A-9Z]$" textfile1.txt | more</span><br><br>Let's look at another series of examples involving <table align="right"><tr valign="top"><td>[[Image:regexps-6.png|thumb|right|220px|Anchoring '''filtering3 digits''' with numbers so only strings containing valid numbers are at the '''beginning''' and '''ending''' of text.]]</td><td>[[Image:regexps-7.png|thumb|right|250px|Anchoring '''3 alpha-numeric characters''' at the '''beginning''' and '''ending''' of text.]]</td></tr></table>What type of strings match this pattern?<br><br># Issue the following Linux command to match strings that '''consist of only 3 digits''':<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[0-9][0-9][0-9]$" textfile1.txt</span><br><br>What did you notice?<br><br># Issue the following Linux command to match strings that '''consist of only 3 alphanumeric digits''':<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[a-zA-Z0-9][a-zA-Z0-9][a-zA-Z0-9]$" textfile1.txt</span><br><br>What did you notice?<br><br>The <span style="font-weight:bold;font-family:courier;">"*"</span> complex regular expression symbol is often confused with the "*" '''filename expansion''' symbol.<br>In other words, it does NOT represent zero or more of '''any character''', but zero or more '''occurrences'''<br>of the character that comes '''before''' the <span style="font-weight:bold;font-family:courier;">"*"</span> symbol.<br><br># To demonstrate, issue the following Linux command to display '''zero or more occurrences''' of the letter "'''x'''":<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "x*" textfile1.txt</span><br><br>You will most likely notice most lines of the file is displayed.<br><br># Let's issue a Linux command to display strings that contain '''more than one occurrence''' of the letter "'''x'''":<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "xx*" textfile1.txt</span><br><br>Why did this work? because the pattern indicates one occurrence of the letter "x",<br>followed by '''zero or MORE occurrences''' of the <u>next</u> letter "x".<br><br>If you combine the complex regular expression symbols <span style="font-weight:bold;font-family:courier;">".*"</span> it will act like<br>zero or more occurrences of <u>any</u> character (i.e. like <span style="font-weight:bold;font-family:courier;">"*"</span> did in filename expansion).<br><br># Issue the following Linux command to match strings begin and end with a number with nothing or anything inbetween:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[0-9].*[0-9]$" textfile1.txt</span><br><br>Using '''simultaneous anchors''' combined with the <span style="font-weight:bold;font-family:courier;">".*"</span> symbol(s) can help you to refine your search patterns of strings.<br><br># Issue the following Linux command to display strings that begin with a capital letter,<br>end with a number, and contains a capital X somewhere inbetween:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[A-Z].*X.*[0-9]$" textfile1.txt</span><br><br>Let's look at another series of examples involving searching for strings that only contain '''valid numbers'''.<br>We will use '''pipeline commands''' to both display stdout to the screen and save to files<br>for confirmation of running these pipeline commands when run a '''checking-script''' later in this investigation.<br><br>

# First, issue the following linux Linux command to download copy another data file called '''numbers1.dat''':<br><span style="color:blue;font-weight:bold;font-family:courier;">wget <nowiki>https://ict.senecacollege.ca/cp ~murray.saululi101/uli101tutorialfiles/numbers1.dat<~/nowiki>regexps</span><br><br># View the contents of the '''numbers.dat''' file using the '''more''' command and quickly view the contents of this file. <br>You should notice '''valid ''' and '''invalid ''' numbers contained in this file. When finished, exit the more command.<br><br># Issue the following linux pipeline command to display only '''whole ''' numbers(i.e. no '''+''' or '''-''' sign):<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[0-9]*$" numbers1.dat | tee faulty.txt | more</span><br><br>You may have noticed that the command '''does not entirely work'''. You may notice an '''empty line '''<br>(which is NOT a whole number). This occurs since the * regular expression symbol represents <br>ZERO or MORE occurrences of a number. You can use an additional numeric character class <br>with the * regular expression symbol to search for one or more occurrences of a number.<br><br># Issue the following linux Linux pipeline command to display only whole numbers:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[0-9][0-9]*$" numbers1.dat | tee whole.txt | more</span><br><br>You should see that this now works.<br><br># Issue the following linux Linux pipeline command to display whole positive or negative <u>only</u> '''signed''' integers:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[+-][0-9][0-9]*$" numbers1.dat | tee signed.txt | more</span><br><br>What did you notice?Positive and negative numbers display, not '''unsigned''' numbers.<br><br>[[Image:regexps-8.png|thumb|right|300px|Simultaneous '''anchoring''' of regular expressions using '''character class''' and '''zero or more occurrences''' to display '''signed''' and '''unsigned''' integers.]]# Issue the following linux Linux pipeline command to display only whole numbers (with '''signed''' or without a positive or negative sign)'''unsigned integers''':<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[+-]*[0-9][0-9]*$" numbers1.dat | tee all.txt | more</span><br><br>Did this command work?<br><br># Issue the following Linux command to check that you created those hard links: <br><span style="color:blue;font-weight:bold;font-family:courier;">bash /home/murray.saul/scripts~uli101/week9-check-1</span><br><br>If you encounter errors, then view the feedback to make corrections, and then re-run the checking script.<br>If you receive a congratulation message that there are no errors, then proceed with this tutorial.<br><br>You can also use the '''grep''' command using ''regular expression'' as a '''filter''' in pipeline commands.<br><br># Issue the following Linux pipeline command:<br><span style="color:blue;font-weight:bold;font-family:courier;">ls | grep "[0-9].*dat$"</span><br><br>What did this pipeline display?<br><br># Issue the following Linux pipeline command:<br><span style="color:blue;font-weight:bold;font-family:courier;">ls | grep "[a-z].*txt$"</span><br><br>What did this pipeline display?<br><br> : Although very useful, '''complex''' regular expressions do NOT <u>entirely</u> solve our problem of displaying<br> '''valid''' unsigned and signed numbers (not to mention displaying decimal numbers).<br><br>In the next investigation, you will learn how to use '''extended''' regular expressions that will completely solve this issue.<br>

Proceed : You can proceed to Investigation INVESTIGATION 2.<br>

<br>In this sectioninvestigation, you will learn how to use '''extended regular expressions''' with the '''egrep''' command<br>to help further refine your search when using regular expressionspatterns.

# Make certain that you are located in your '''~/regexps''' directory on your ''Matrix'' account.<br><br># Issue the following linux pipeline Linux command to download copy another data file called '''numbers2.dat''':<br><span style="color:blue;font-weight:bold;font-family:courier;">wget <nowiki>https:/cp ~uli101/ict.senecacollege.ca/~murray.saul/uli101tutorialfiles/numbers2.dat<~/nowiki></span><br><br># View the contents of the '''numbers2.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.<br><br># 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''':<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[+-]*[0-9][0-9]*$" numbers2.dat | more</span><br><br>You should notice '''multiple + ''' '''+''' or '''- ''' '''signs are appearing as well. This occurs since ''' appear <u>prior</u> to some numbers.<br>This occurs since you are searching or one or MORE occurrences of a + or - sign.<br><br>Using '''extended regular expression''' symbols to specify '''minimum and maximum repetitions '''{min,max}and '''maximum''' repetitions: '''{min,max}''' can solve this that problem.<br><br># Issue the following linux pipeline Linux command (using extended regular expression symbols) <br>to display only whole numbers (with '''signed''' or without a positive or negative sign)'''unsigned integers''':<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[+-]{0.,1}[0-9]{1,}$" numbers2.dat | more</span><br><br>'''NOTE:No output will be displayed! Why?''' most likely, there were '''NO results'''. <br><br>This is due to the fact that the '''grep command was NOT issued correctly to use extended regular expression symbols'''. <br>You would need to issue either '''grep -E''' (, or more simply) just issue the '''egrep''' command. The egrep command works with <br>'''all ''' regular expression symbols, and should be used in the future <u>instead </u> of the older grep command.<br><br># Reissue the above pipeline command using We will use '''egreppipeline commands''' instead of ''grepto both display stdout to the screen and save to files<br>for confirmation of running these pipeline commands when run a '''checking-script''':later in this investigation.<br><span style="colorbr># Issue the following Linux pipeline command using '''egrep''' instead of ''grep'':<br><span style="color:blue;font-weight:bold;font-family:courier;">egrep "^[+-]{0,1}[0-9]{1,}$" numbers2.dat | moretee better-number1.txt</span><br><br>You should have noticed that the command worked correctly this time because you used the [[Image:eregexps-2.png|thumb|right|300px|Using '''egrepextended''' regular expression symbols (such as '''repetition''') to refine matches of ''signed'' and ''unsigned'' commandintegers.]]You should have noticed that the command worked correctly this time because you used the '''egrep''' command.<br><br># Issue '''NOTE:''' With extended regular expressions, the following linux pipeline command '''?''' symbol can be used to display signed, unsigned, wholerepresent the '''{0, 1}''' repetition symbols and decimal numbers:<br><span style="color:blue;font-weight:bold;the '''+''' symbol can be used to represent the '''{1,}''' repetition symbols<br><br># Issue the following Linux pipeline command using the repetition shortcuts <span style="font-familyweight:courierbold;font-family:courier;">egrep "^[+"</span> and <span style="font-]{0,1}[0weight:bold;font-9]{1,}[.]{0,1}[0-9]*$" numbers2.dat | more</span>family:courier;">"?"</span>:<br><br>You can also use extended regular expression symbols for '''grouping'''. For example, you can search for repetitions of GROUPS of characters<brspan style="color:blue;font-weight:bold;font-family:courier;">(like a word) as opposed to just a single character or a GROUP of numbers as opposed to a single digitegrep "^[+-]?[0-9]+$" numbers2.<dat | tee better-number2.txt</span><br><br>You should have seen the '''same results''', but less typing was required.<br><br># Issue the following linux Linux pipeline command to download another data file called display '''signed''', '''unsigned''words.dat', '''whole''', and '''decimal''' numbers:<br><span style="color:<br><span style="color:blue;font-weight:bold;font-family:courier;">wget <nowiki>https://ictegrep "^[+-]{0,1}[0-9]{1,}[.senecacollege.ca/~murray]{0,1}[0-9]*$" numbers2.saul/uli101/wordsdat | tee better-number3.dat</nowiki>txt</span><br><br># View the contents of Were all signed and unsigned intergers and decimal numbers displayed?<br><br># Issue the follwoing command to check that you correctly issued<br>those ''Linux pipeline commands'numbers2.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;">~uli101/week9-check-2</span><br><br># Issue If you encounter errors, then view the following linux pipeline command feedback to display two or more occurrences of make corrections, and then re-run the word "the":checking script.<br>If you receive a congratulation message that there are no errors, then proceed with this tutorial.<span style="color:blue;font-weight:bold;font-family:courier;"br><br>egrep -i "(the){2,}" wordsYou can also use extended regular expression symbols for '''grouping'''.dat | more</span><br>For example, you can search for repetitions of GROUPS of characters (like a word)<br>'''NOTE:''' You should NOT see any output due as opposed to just a single character or a GROUP of numbers as opposed to the fact that a single digit.<ubr>space</ubr> should be included at # Issue the end of the word "following linux pipeline command to copy another data file called '''thewords.dat'''". Usually words are separated by spaces:<br><span style="color:blue;font-weight:bold;font-family:courier; 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).>cp ~uli101/tutorialfiles/words.dat ~/</span><br><br># Reissue View the contents of the previous pipeline '''words.dat''' file using the '''more''' command including a space in brackets:and quickly view the contents of this file.<br>Within this file, you should notice some lines that contain repetitions of words. When finished, exit the more command.<br><span style="color:blue;font-weight:bold;font-family:courier;"br>egrep -i "(# Issue the ){2,}following linux pipeline command to display '''two or more occurrences''' of the word " words.dat | more</span>the":<br><br>The span style="|color:blue;font-weight:bold;font-family:courier;">egrep -i " (orthe) symbol can be used within the grouping {2,}" words.dat | tee word-search1.txt symbols to allow matching of additional groups of characters.<brmore</span>Again, it is important to follow the character groupings with the space character<br><br># Issue the following linux pipeline command to search for 2 or more occurrences of the word "'''the''NOTE: No output is displayed! Why?'''" <ubr>or<br>This is due to the fact that a <u>space</u> should be included at the end of the word "'''andthe'''":.<br><span style="color:blue;font-weight:bold;font-family:courierUsually words are separated by spaces;therefore, there were no matches since there were not occurrences<br>of "thethe" as opposed to "'''the the'''">egrep -i "(the |and ){2,}" words(i.e. no space after repetition of the pattern).<br><br># Reissue the previous pipeline command with the word the followed by a '''space''' within the brackets:<br><span style="color:blue;font-weight:bold;font-family:courier;">egrep -i "(the ){2,}" words.dat | tee word-search2.txt</span><br><br>[[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 <span style="font-weight:bold;font-family:courier;">"|"</span> (or) symbol (same symbol as "pipe") can be used within the grouping symbols to allow matching of additional groups of characters.<br>Again, it is important to follow the character groupings with the space character<br><br># Issue the following linux pipeline command to search for '''two or more occurrences''' of the word "'''the '''" <u>or</u> '''two or more occurrences''' of the word "'''and '''":<br><span style="color:blue;font-weight:bold;font-family:courier;">egrep -i "(the |and ){2,}" words.dat | tee word-search3.txt</span><br><br># Issue the following Linux command to check that you correctly issued<br>those ''Linux pipeline commands'' using the '''tee''' command to create those text files:<br><span style="color:blue;font-weight:bold;font-family:courier;">~uli101/week9-check-3</span><br><br>If you encounter errors, then view the feedback to make corrections, and then re-run the checking script.<br>If you receive a congratulation message that there are no errors, then proceed with this tutorial.<br><br>Let's issue a Linux '''pipeline''' command using the '''egrep''' command as a '''filter'''<br>using <u>both</u> '''complex''' and '''extended''' regular expressions.<br><br># Issue the following Linux pipeline command:<br><span style="color:blue;font-weight:bold;font-family:courier;">ls | egrep "[a-z]{1,}.*[0-9]"</span><br><br>What did this Linux pipeline command display?<br><br>: The '''grep''' and '''egrep''' Linux commands are NOT the only Linux commands that use regular expressions.<br>In the next investigation, you will apply regular expressions to a number of Linux commands<br>that you already learned in this course.dat | more</span><br><br>

Proceed : You can proceed to Investigation INVESTIGATION 3<br><br>

=INVESTIGATION 3: OTHER COMMANDS THAT USE USING REGULAR EXPRESSIONS =<br>In this sectioninvestigation, you will see how regular expressions can be used with other Linux utilities commands other than '''grep''' or '''egrep'''that can use regular expressions.

# Make certain that you are located in your '''~/regexps''' directory on your ''Matrix'' account.<br><br># Let's look at using regular expressions with the '''man ''' command.<br>Issue the following linux command :<br><span style="color:blue;font-weight:bold;font-family:courier;">man ls</span><br><br>[[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.<br>Type the following regular expression below and press '''ENTER''':<br><span style="color:blue;font-weight:bold;font-family:courier;">/sort</span><br><br>'''FYI:''' The '''grep''' and '''egrep''' linux Linux commands contain the regular expressions within quotes,<br>but '''most ''' other Linux commands specify regular expressions using forward slashes<br>'''forward slashes''' (e.g. '''<span style="font-weight:bold;font-family:courier;">/regular expression</''' span> &nbsp; or '''&nbsp; <span style="font-weight:bold;font-family:courier;">/regular expression'''/</span>).<br><br># Scroll throughout the man pages for the ls command to view matches for the pattern "'''sort'''"<br>(You can press '''SPACE''' and or key combination '''&lt;ALT&gt;&lt;alt-b&gt;''' to move forward and backwards per page one screen respectively).<br><br># Press the letter <span style="color:blue;font-weight:bold;font-family:courier;">q</span> to '''exit ''' the ''man '' pages for '''ls'''.<br><br>#Let's use regular expressions with the '''moreless''' command.<br><br># Issue the following linux Linux command to view the contents of the copy another data file called '''textfile1large-file.txt''' (downloaded in a previous section):<br><span style="color:blue;font-weight:bold;font-family:courier;">more textfile1cp ~uli101/tutorialfiles/large-file.txt~/</span><br><br>#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.<br>Type ]]# Issue the following regular expression and press ENTERLinux command to view the contents of the '''large-file.txt''':<br><span style="color:blue;font-weight:bold;font-family:courier;">/uli101less large-file.txt</span><br><br>What did you notice?<br><br>#Search We want to search for the next occurrence of the a pattern '''uli101''' by '''re-typing''' within this text file.<br>Type the following regular expression and pressing press ENTER:<br><span style="color:blue;font-weight:bold;font-family:courier;">/uli101</span><br><br>you You should now see the '''second occurrence''' of this pattern within "uli101" throughout the text file.<br><br># Press the letter <span style="color:blue;font-weight:bold;font-family:courier;">q</span> to exit the '''moreless''' command.<br><br>#Try the same search techniques with the '''more''' command.<br><br>Does it work the same for the ''less'' command?<br><br>[[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 <br>by using regular expressions.<br><br># Issue the following linux Linux command to edit the '''textfile1large-file.txt''' file:<br><span style="color:blue;font-weight:bold;font-family:courier;">vi textfile1large-file.txt</span><br><br>Let's first perform a simple search within this text file.<br><br># Press the '''ESC''' key to make certain you are in '''COMMAND''' mode.<br><br># Type the following and press '''ENTER''':<br><span style="color:blue;font-weight:bold;font-family:courier;">/uli101</span><br><br>You should move to the '''first occurrence''' of notice the pattern: "'''uli101'''" highlighted for ALL occurrences in this text file.<br><br>Let's '''search ''' for the '''uli101''' pattern, but and '''replace ''' it in capitals (i.e '''ULI101''').<br><br>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 .<br>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''').<br><br>[[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,<br>type the following and press '''ENTER''':<br><span style="color:blue;font-weight:bold;font-family:courier;">:%s/uli101/ULI101/g</span><br><br>You should have noticed that the first occurrence of uli101 has been changed to ULI101.<br><br># Navigate throughout the text file to see if the other occurrences have been replaced.<br><br>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).<br><br># Making certain that you are command mode in vi, type Type the following (in uppercase letters) and press '''ENTER''':<br><span style="color:blue;font-weight:bold;font-family:courier;">:%s/uli101/ULI101/g</span><br><br>You should notice the pattern "'''ULI101'''" highlighted for ALL occurrences in this text file.<br><br># Navigate throughout the text file to confirm that ALL occurrences of '''uli101 ''' have been <u>replaced </u> with '''ULI101'''.<br><br># Save changes to your vi editing session and exit by typing the following and pressing ENTER:<br><span style="color:blue;font-weight:bold;font-family:courier;">:wxx</span># After you complete the Review Questions sections to get additional practice, then work on your<br>online assignment 3.<br><br>

https://ictwiki.cdot.senecacollege.ca/~murray.saululi101/uli101files/uli101_command_practice_9a.docx

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

1. <span style="font-family:courier;font-weight:bold">grep plym ~murray.saul/uli101/cars</span><br>2. <span style="font-family:courier;font-weight:bold">grep -i fury ~murray.saul/uli101/cars</span><br>3. <span style="font-family:courier;font-weight:bold">grep “^[m-z]” ~murray.saul/uli101/cars</span><br>4. <span style="font-family:courier;font-weight:bold">grep -i “^[m-z]” ~murray.saul/uli101/cars</span><br>5. <span style="font-family:courier;font-weight:bold">grep “3$” ~murray.saul/uli101/cars</span><br>6. <span style="font-family:courier;font-weight:bold">grep -i “c.*5$” ~murray.saul/uli101/cars</span><br>

https://ictwiki.cdot.senecacollege.ca/~murray.saululi101/uli101files/uli101_command_practice_9b.docx

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

1. <span style="font-family:courier;font-weight:bold">grep "^[-+]" ~murray.saul/uli101/numbers.txt</span><br>2. <span style="font-family:courier;font-weight:bold">grep "^[-+]*.[0-9]" ~murray.saul/uli101/numbers.txt</span><br>3. <span style="font-family:courier;font-weight:bold">grep "^[+-]?[0-9]" ~murray.saul/uli101/numbers.txt</span><br> &nbsp; &nbsp;(Why?)<br>4. <span style="font-family:courier;font-weight:bold">egrep "^[+-]?[0-9]" ~murray.saul/uli101/numbers.txt</span><br>5. <span style="font-family:courier;font-weight:bold">egrep "^[+-]?[0-9]+$" ~murray.saul/uli101/numbers.txt</span><br>6. <span style="font-family:courier;font-weight:bold">egrep "^[+-]?[0-9]+[.]?[0-9]+$" ~murray.saul/uli101/numbers.txt</span><br>

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