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=USING REGULAR EXPRESSIONS=
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= INVESTIGATION 1: SIMPLE & COMPLEX REGULAR EXPRESSIONS =
<span style="color:red;">'''ATTENTION''': The due date for successfully completing this tutorial (i.e. tutorial 89) is by Friday, December 15 April 21 @ 11:59 PM (Week 14).</span><br>
In this investigation, 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.
# Make certain that you are located in your '''~/regexps''' directory on your ''Matrix'' account.<br><br>
# Issue the following Linux command to copy another data file called '''numbers2.dat''':<br><span style="color:blue;font-weight:bold;font-family:courier;">cp ~osl640/tutorial9/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 ''invalid'' numbers contained in this file. When finished, exit the more command.<br><br>[[Image:eregexps-1.png|thumb|right|300px|'''Weakness''' of '''complex''' regular expressions that do not '''limit''' the number of '''positive''' or '''negative''' signs.]]
# Issue the following Linux command to display '''signed''' or '''unsigned integers''':<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[+-]*[0-9][0-9]*$" numbers2.dat</span><br><br>You should notice '''multiple''' '''+''' or '''-''' '''signs''' appear <u>prior</u> to some numbers.<br>This occurs since you are searching or one or MORE occurrences of a + or - sign.<br><br>Using '''extended regular expression''' symbols to specify '''minimum''' and '''maximum''' repetitions: '''{min,max}''' can solve that problem.<br><br>
Write the results of each of the following Linux commands using regular expressions for the above-mentioned file.
1. <span style="font-family:courier;font-weight:bold">grep "^[-+]" ~murray.saulosl640/uli101tutorial9/numbers.txt</span><br>2. <span style="font-family:courier;font-weight:bold">grep "^[-+]*.[0-9]" ~murray.saulosl640/uli101tutorial9/numbers.txt</span><br>3. <span style="font-family:courier;font-weight:bold">grep "^[+-]?[0-9]" ~murray.saulosl640/uli101tutorial9/numbers.txt</span><br> (Why?)<br>4. <span style="font-family:courier;font-weight:bold">egrep "^[+-]?[0-9]" ~murray.saulosl640/uli101tutorial9/numbers.txt</span><br>5. <span style="font-family:courier;font-weight:bold">egrep "^[+-]?[0-9]+$" ~murray.saulosl640/uli101tutorial9/numbers.txt</span><br>6. <span style="font-family:courier;font-weight:bold">egrep "^[+-]?[0-9]+[.]?[0-9]+$" ~murray.saulosl640/uli101tutorial9/numbers.txt</span><br>
11. Write a Linux command to display all lines in the file called '''~/data.txt''' that begins with a minimum of 2 occurrences<br> and a maximum of 4 occurrences of the word “the” or the word “but” (upper or lower case).
[[Category:OSL640]]
