View source for Tutorial9: Regular Expressions

=USING REGULAR EXPRESSIONS=
<br>
===Main Objectives of this Practice Tutorial===

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

:* Explain the difference between '''Regular Expressions''' and '''Filename Expansion'''

:* Explain the purpose of '''Literal (Simple)''' Regular Expressions

:* Understand and use common symbols for '''Complex''' Regular Expressions and their purpose

:* Understand and use command symbols for '''Extended''' Regular Expressions and their purpose

:* List various Linux commands (other than '''grep''' or '''egrep''') that use regular expressions

===Tutorial Reference Material===

{|width="100%" cellspacing="0" cellpadding="10"

|- valign="top"

|colspan="2" style="font-size:16px;font-weight:bold;border-bottom: thin solid black;border-spacing:0px;"|Course Notes<br>

|colspan="2" style="font-size:16px;font-weight:bold;border-bottom: thin solid black;border-spacing:0px;padding-left:15px;"|Linux Command/Shortcut Reference<br>

|colspan="1" style="font-size:16px;font-weight:bold;border-bottom: thin solid black;border-spacing:0px;padding-left:15px;"|YouTube Videos<br>

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

|colspan="2" |Course Notes:<ul><li>[https://ict.senecacollege.ca/~murray.saul/uli101/ULI101-Week9.pdf PDF] | [https://ict.senecacollege.ca/~murray.saul/uli101/ULI101-Week9.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)]<br><br>


|  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://man7.org/linux/man-pages/man1/more.1.html more] / [https://www.man7.org/linux/man-pages/man1/less.1.html less]
* [https://man7.org/linux/man-pages/man1/vi.1p.html vi] / [http://linuxcommand.org/lc3_man_pages/vim1.html vim]
* [https://man7.org/linux/man-pages/man1/sed.1p.html sed]
* [https://man7.org/linux/man-pages/man1/awk.1p.html awk]
* [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 =

<i>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. </i><br>Reference:  https://en.wikipedia.org/wiki/Regular_expression

===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 to expand filenames as arguments (referred to as “globbing”).]]</td><td>[[Image:re-2.png|thumb|right|250px|'''Concept''' of matching a simple pattern of text contained within a text file.]]</td></table>In 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''', '''more''', '''head''', '''tail''', '''sort''', '''uniq''', '''cut''', '''tr''', and '''wc'''.<br><br>

<i>A '''regular expression''' is a combination of two types of characters: '''literals''' and '''special characters'''.<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/

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

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

[[Image:re-3.png|thumb|right|250px|The simplest regular expression is a series of letters and numbers, possibly including white space (tabs or space characters).]]The simplest regular expression is a series of letters and numbers, possibly including white space (tabs or space characters), that have no special meaning. Such a regular expression consists of ``literals''; that is, normal letters, which match only an identical letter in the data being searched.<br><br>For example:
"This is a regular expression"<br><br>
<i>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.</i> <br>Reference: http://osr507doc.xinuos.com/en/OSUserG/_Literal_chars_in_regexps.html

===Complex 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 “'''the'''” would be matched for larger word containing that pattern like '''there''', '''they''', '''either''', '''them''', '''their''', etc.<br>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).

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:

:*'''Anchors: ''' <span style="font-family:courier;font-weight:bold;">^</span> , <span style="font-family:courier;font-weight:bold;">$</span><br>Match lines the begin (^) or end ($) with a pattern.<br><br>
:*'''Single Character:''' &nbsp; <span style="font-family:courier;font-weight:bold;">.</span><br>Represents a single character that can be any type of character.<br><br>
:*'''Character Class:'''  <span style="font-family:courier;font-weight:bold;">[ ]</span> , <span style="font-family:courier;font-weight:bold;">[^ ]</span><br>Represents a single character but with restrictions.<br><br>
:*'''Zero or More Occurrence:'''  <span style="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|220px|Example of using '''anchors'''.]]</td><td>[[Image:re-5.png|thumb|right|200px|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===
 
'''Extended Regular Expressions''' consist of additional special characters<br> to “extend” the capability of regular expressions:


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

:*'''Grouping: ( )'''<br>Perhaps you want to search for repetition for a group of characters, a word, or a phase.<br>You can enclose them within brackets ( ) to specify a group.

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

Examples of how to use these complex regular expressions with the '''egrep''' command are displayed below:<br><br>

<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 '''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>

=INVESTIGATION 1: SIMPLE &amp; COMPLEX REGULAR EXPRESSIONS=

<br>
In this section, 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.


'''Perform the Following Steps:'''

# '''Login''' to your matrix account.<br><br>
# Issue a command to '''confirm''' you are located in your '''home''' directory.<br><br>The '''wget''' command is used to download files from the Internet to your shell.<br>This will be useful to download '''text files''' and '''data files''' that we will be using for this tutorial.<br><br>
# Issue the following linux command to download a text file to your home directory:<br><span style="color:blue;font-weight:bold;font-family:courier;">wget <nowiki>https://ict.senecacollege.ca/~murray.saul/uli101/textfile1.txt</nowiki></span><br><br>
# Issue the '''ls''' command to confirm that the text file was downloaded.<br><br>
# View the contents of the '''textfile1.txt''' file using the '''more''' command and quickly view the contents of this file.<br><br>Although there are several Linux commands that use regular expressions,<br>we will only be using the '''grep''' command for this investigation.<br><br>
#Issue the following linux pipeline command to match the pattern the within '''textfile1.txt''':<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "the" textfile1.txt</span><br><br>Take a few moments to view the output and observe the matched pattern.<br><br>
# Now, issue the grep linux pipeline command with the '''-i''' option to ignore case sensitively:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep -i "the" textfile1.txt</span><br><br>What do you notice is different with this pipeline command?<br><br>You will notice that the pattern "'''the'''" is matched including larger words like "'''them'''" and "'''their'''".<br>You can issue the '''grep''' command with the -w option to only match the pattern as a '''word'''.<br><br>
# Issue the following linux pipeline command:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep -w -i "the" textfile1.txt</span><br><br>You should now see only strings of text that match the word '''"the"''' (upper or lower case).<br><br>Matching literal or simple regular expressions can be useful, but are '''limited'''<br>in what they can assist with pattern matching. For example, you may want to<br>search for a pattern located at the '''beginning''' or '''end''' of the string.<br><br>There are other regular expression symbols that provide more '''precise''' pattern matches.<br>These special characters are known as '''complex''' and '''extended''' regular expressions symbols.<br> In this section, we will focus on '''complex regular expressions''' and then discuss<br>'''extended regular expressions''' in '''investigation 2'''.<br><br>
# Issue the following Linux pipeline command:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep -w -i "^the" textfile1.txt</span><br><br>The '''^''' symbol is referred to as an '''anchor'''. In this case, it only matches<br>the word "'''the'''" (both upper or lowercase) at the <u>beginning</u> of the string.<br>The '''$''' symbol is used to anchor patterns at the end of strings.<br><br>
# Issue the following Linux pipeline command:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep -w -i "the$" textfile1.txt</span><br><br>What do you notice?<br><br>
# Issue the following Linux pipeline command to anchor the '''word''' "the" simultaneously<br>at the <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$" textfile1.txt </span><br><br>What do you notice?<br><br>Anchoring patterns at both the <u>beginning</u> and <u>ending</u> of strings can greatly assist<br>for more robust search patterns.<br><br>We will now be demonstrating the usefulness of  '''simultaneous anchoring'''<br>with other complex regular expressions symbols.<br><br>
# Issue the following command to match strings that begin with 3 characters:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^..." textfile1.txt</span><br><br>What do you notice? Can lines that contain '''less than 3 characters''' be displayed?<br><br>
# Issue the following command to match strings that begin and end with 3 characters:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^...$" textfile1.txt</span><br><br>What do you notice compared to the previous command?<br><br>
# Issue the following command to match strings that begin with 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 command to match strings that end with 3 uppercase letters:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "[A-Z][A-Z][A-Z]$" textfile1.txt</span><br><br>Did any lines match this pattern?<br><br>
# Issue the following command to match strings that consist of only 3 digits:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[0-9][0-9][0-9]$" textfile1.txt</span><br><br>What did you notice?<br><br>The <span style="font-weight:bold;font-family:courier;">"*"</span> complex regular expression symbol is often confused with filename expansion.<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 "*" symbol.<br><br>
# To demonstration, issue the following 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 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 letter "x".<br><br>If you combine the complex regular expression symbols ".*" it will act like<br>zero or more occurrences of any character (i.e. like "*" did in filename expansion).<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-weight:bold;font-family:courier;">grep "^[0-9].*[0-9]$" textfile1.txt</span><br><br>Using '''simultaneous anchors''' combined with the ".*" symbol(s) can help you to refine your search patterns of strings.<br><br>
# Issue the following linux pipeline command to display strings that begin with a capital letter,<br>end with a number, and contains a capital X somewhere inbetween:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[A-Z].*X.*[0-9]$" 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>
# Issue the following Linux command to create the '''regexps''' directory: <span style="color:blue;font-weight:bold;font-family:courier;">mkdir ~/regexps</span><br><br>
# Change to the '''regexps''' directory and confirm that you have moved to this directory.<br><br>
# First, issue the following linux command to download another data file called '''numbers1.dat''':<br><span style="color:blue;font-weight:bold;font-family:courier;">wget <nowiki>https://ict.senecacollege.ca/~murray.saul/uli101/numbers1.dat</nowiki></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 command to display only whole numbers:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[0-9]*$" numbers1.dat | tee faulty.txt</span><br><br>You may have noticed that the command does not entirely work. You may notice an empty line<br>(which is NOT a whole number). This occurs since the * regular expression symbol represents<br>ZERO or MORE occurrences of a number. You can use an additional numeric character class<br>with the * regular expression symbol to search for one or more occurrences of a number.<br><br>
# Issue the following linux command to display only whole numbers:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[0-9][0-9]*$" numbers1.dat | tee whole.txt</span><br><br>You should see that this now works.<br><br>
# Issue the following linux command to display whole positive or negative integers:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[+-][0-9][0-9]*$" numbers1.dat | tee signed.txt</span><br><br>What did you notice?<br><br>
# Issue the following linux command to display only whole numbers (with or without a positive or negative sign):<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[+-]*[0-9]*$" numbers1.dat | tee all.txt</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/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>

:Proceed to INVESTIGATION 2.

=INVESTIGATION 2: EXTENDED REGULAR EXPRESSIONS =

In this section, you will learn how to use '''extended regular expressions''' to help refine your search when using regular expressions.


'''Perform the Following Steps:'''

# Make certain that you are located in your '''~/regexps''' directory on your ''Matrix'' account.<br><br>
# Issue the following linux pipeline command to download another data file called '''numbers2.dat''':<br><span style="color:blue;font-weight:bold;font-family:courier;">wget <nowiki>https://ict.senecacollege.ca/~murray.saul/uli101/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 the following linux pipeline command to display only whole numbers (with or without a positive or negative sign):<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[+-]*[0-9][0-9]*$" numbers2.dat</span><br><br>You should notice '''multiple''' '''+''' or '''-''' '''signs''' appear <u>prior</u> to some numbers.<br>This occurs since you are searching or one or MORE occurrences of a + or - sign.<br><br>Using '''extended regular expression''' symbols to specify '''minimum''' and '''maximum''' repetitions: '''{min,max}''' can solve that problem.<br><br>
# Issue the following linux pipeline command (using extended regular expression symbols)<br>to display only whole numbers (with or without a positive or negative sign):<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[+-]{0.1}[0-9]{1,}$" numbers2.dat</span><br><br>'''NOTE:''' 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) 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.<br><br>
# Reissue the above pipeline command using '''egrep''' instead of ''grep'':<br><span style="color:blue;font-weight:bold;font-family:courier;">egrep "^[+-]{0,1}[0-9]{1,}$" numbers2.dat | tee better-number1.txt</span><br><br>You should have noticed that the command worked correctly this time because you used the '''egrep''' command.<br><br>'''NOTE:''' In extended regular expressions, the '''?''' symbol can be used to represent the '''{0,1}''' repetition symbols<br>and the '''+''' symbol can be used to represent the '''{1,}''' repetition symbols<br><br>
# Reissue the above pipeline command using '''egrep''' instead of ''grep'':<br><span style="color:blue;font-weight:bold;font-family:courier;">egrep "^[+-]?[0-9]+$" numbers2.dat | tee better-number2.txt</span><br><br>You should have seen the same results, but the extended regular expression required less typing.<br><br>
# Issue the following linux pipeline command to display signed, unsigned, whole, and decimal numbers:<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</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;">bash /home/murray.saul/scripts/week9-check-2</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 extended regular expression symbols for '''grouping'''.<br>For example, you can search for repetitions of GROUPS of characters (like a word)<br>as opposed to just a single character or a GROUP of numbers as opposed to a single digit.<br><br>
# Issue the following linux pipeline command to download another data file called '''words.dat''':<br><span style="color:blue;font-weight:bold;font-family:courier;">wget <nowiki>https://ict.senecacollege.ca/~murray.saul/uli101/words.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 the following linux pipeline command to display two or more occurrences of the word "the":<br><span style="color:blue;font-weight:bold;font-family:courier;">egrep -i "(the){2,}" words.dat | tee word-search1.txt  more</span><br><br>'''NOTE:''' You should NOT see any output due to the fact that a <u>space</u> should be included at the end of the word "'''the'''".<br>Usually words are separated by spaces; therefore, there were no matches since there were not occurrences<br>of "thethe" as opposed to "'''the the'''" (i.e. no space after repetition of the pattern).<br><br>
# Reissue the previous pipeline command including a space in 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>The "|" (or) symbol 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 2 or more occurrences of the word "'''the'''" <u>or</u> 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;">bash /home/murray.saul/scripts/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>

:Proceed to INVESTIGATION 3

=INVESTIGATION 3: OTHER COMMANDS THAT USE REGULAR EXPRESSIONS =

In this section, you will see how regular expressions can be used with other Linux utilities other than '''grep''' or '''egrep'''.


'''Perform the Following Steps:'''

# 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>
# 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 commands contain the regular expressions within quotes,<br>but most other Linux commands specify regular expressions using forward slashes<br>(e.g. '''/regular expression/''' or '''/regular expression''').<br><br>
# Scroll throughout the man pages for the ls command to view matches for the pattern "'''sort'''"<br>(You can press '''SPACE''' or key combination '''alt-b''' to move forward and backwards 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 '''more''' command.<br>Issue the following linux command to view the contents of the '''textfile1.txt''' (downloaded in a previous section):<br><span style="color:blue;font-weight:bold;font-family:courier;">more textfile1.txt</span><br><br>
#We want to search for a pattern '''uli101''' within this text file.<br>Type the following regular expression and press ENTER:<br><span style="color:blue;font-weight:bold;font-family:courier;">/uli101</span><br><br>What did you notice?<br><br>
#Search for the next occurrence of the pattern '''uli101''' by '''re-typing''' the following regular expression and pressing ENTER:<br><span style="color:blue;font-weight:bold;font-family:courier;">/uli101</span><br><br>you should now see the '''second occurrence''' of this pattern within the text file.<br><br>
# Press the letter <span style="color:blue;font-weight:bold;font-family:courier;">q</span> to exit the '''more''' command.<br><br>
#Let's learn how to perform a simple '''search and replace''' within the '''vi''' utility by using regular expressions.<br>Issue the following linux command to edit the '''textfile1.txt''' file:<br><span style="color:blue;font-weight:bold;font-family:courier;">vi textfile1.txt</span><br><br>Let's first perform a simple search within this text file.<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 the pattern: '''uli101'''.<br><br>Let's search for the '''uli101''' pattern, but replace it in capitals (i.e '''ULI101''').<br><br>In vi, in order to perform and command, you need to go into last line mode, and then issue a command to apply to the entire text file, followed by a regular expression to search for and a regular expression to replace (i.e. '''/search/replace/''').<br><br>
# Type the following and press ENTER:<br><span style="color:blue;font-weight:bold;font-family:courier;">:%s/uli101/ULI101</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 the other two occurrences. In order to replace for ALL occurrences, you need to add the letter g (meaning "'''global'''") at the end of the last forward slash (e.g /'''search/replace/g''').<br><br>
# Making certain that you are command mode in vi, type the following and press ENTER:<br><span style="color:blue;font-weight:bold;font-family:courier;">:%s/uli101/ULI101/g</span><br><br>
# Navigate throughout the text file to confirm that ALL occurrences of uli101 have been replaced 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;">:wx</span><br><br>
: After you complete the Review Questions sections to get additional practice, then work on your<br>'''online assignment 3'''.
<br><br>

= LINUX PRACTICE QUESTIONS =

The purpose of this section is to obtain '''extra practice''' to help with '''quizzes''', your '''midterm''', and your '''final exam'''.
<br><br>
==REVIEW QUESTIONS: SIMPLE &amp; COMPLEX REGULAR EXPRESSIONS==

Here is a link to the MS Word Document of ALL of the questions displayed below but with extra room to answer on the document to
simulate a quiz:

https://ict.senecacollege.ca/~murray.saul/uli101/uli101_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 &amp; Complex Regular Expressions'''

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



'''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<br>
8.	Write a Linux command to display all lines in the file called '''~/text.txt''' that contains the word:
the<br>
9.	Write a Linux command to display all lines in the file called '''~/text.txt''' that begin with a number.<br>
10.	Write a Linux command to display all lines in the file called '''~/text.txt''' that end with a letter
(either upper or lowercase).<br>
11.	Write a Linux command to display all lines in the file called '''~/text.txt''' that begin and end with a number.<br>
12.	Write a Linux command to display all lines in the file called '''~/text.txt''' that contains exactly 3 characters that can be anything.<br>
13.	Write a Linux command to display all lines in the file called '''~/text.txt''' that contains exactly 3 numbers.<br>
14.	Write a Linux command to display all lines in the file called '''~/text.txt''' that contains 1 or more “C” characters.<br>

<br><br>

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

Here is a link to the MS Word Document of ALL of the questions displayed below but with extra room to answer on the document to
simulate a quiz:

https://ict.senecacollege.ca/~murray.saul/uli101/uli101_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).
<br><br>
'''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.	<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>


'''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<br> &nbsp; &nbsp; &nbsp; of the word “the” <u>or</u> 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<br> &nbsp; &nbsp; &nbsp; and a maximum of 4 occurrences of the word “the” or the word “but” (upper or lower case).


 


[[Category:ULI101]]