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→INVESTIGATION 1: SIMPLE & COMPLEX REGULAR EXPRESSIONS
# 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 | more</span><br><br>Why did this work? 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 the complex regular expression symbols .* it will act like zero or more occurrence of any character (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]$" textfile1.txt | more</span><br><br>Using simultaneous anchors combined with the .* symbol(s) can help you to refine your search patterns of strings.<br><br>
# Issue the following linux pipeline command to display strings that begin with a capital letter, ends with a number, and contains a capital X somewhere inbetween:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[A-Z].*X.*[0-9]$" textfile1.txt | more</span><br><br>Let's look at another series of examples involving '''error-checking ''' with numbers so only strings containing valid numbers are displayed.<br><br>
# First, issue the following linux command to download another data file called numbers.dat:<br><span style="color:blue;font-weight:bold;font-family:courier;">wget <nowiki>https://ict.senecacollege.ca/~murray.saul/uli101/numbers.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. You should notice valid and invalid numbers contained in this file. When finished, exit the more command.<br><br>