View source for Tutorial 9 - Regular Expressions

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

:* Define the term '''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 several Linux commands that can use regular expressions
<br>

===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 =

===Regular Expressions===

<i>A '''regular expression''' is a combination of two types of characters: '''literals''' and '''special characters'''.<br>Strings of text can be compared to this pattern to see if there is a match.</i>

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'''.
<br><br>

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

[[Image:re-3.png|thumb|right|200px|A '''simple''' ('''literal''') regular expression is a series of letters and numbers (tabs or spaces).]]
The simplest regular expression is a series of letters and numbers, (tabs or spaces).<br>A '''simple''' ('''literal''') regular expression consists of normal characters, which used to match patterns.<br><br>
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.<br><br>
For example:
<span style="color:blue;font-weight:bold;font-family:courier;">grep Linux document.txt</span><br><br>

=== Complex / Extended Regular Expressions ===

'''Complex Regular Expressions'''
<br><br>
The problem with just using '''simple''' ('''literal''') regular expressions is that only <u>simple</u> or <u>general</u> patterns are matched. 

''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:''' &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 '''complex regular expressions''' are displayed below:

<table align="left"><tr valign="top"><td>[[Image:re-4.png|thumb|right|200px|Example of using '''anchors'''.]]</td><td>[[Image:re-5.png|thumb|right|175px|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>

 
'''Extended Regular Expressions'''

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


:'''Repetition:''' <span style="color:blue;font-family:courier;font-weight:bold;">{min,max}</span><br>Allows for more precise repetitions. Using braces, you can specify<br>the '''minimum''' and/or '''maximum''' number of repetitions.

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

:'''or Condition:'''  <span style="color:blue;font-family:courier;font-weight:bold;">|</span><br>Can be used with '''groups''' 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 '''extended 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 '''groups'''.]]</td><td>[[Image:re-10.png|thumb|right|250px|Example of using '''or''' condition with '''groups'''.]]</td></tr></table>
<br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br>
= INVESTIGATION 1: SIMPLE & COMPLEX REGULAR EXPRESSIONS =

= INVESTIGATION 2: EXTENDED REGULAR EXPRESSIONS =

= INVESTIGATION 3: OTHER COMMANDS THAT USE REGULAR EXPRESSIONS =

= LINUX PRACTICE QUESTIONS =