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→INVESTIGATION 1: SIMPLE & COMPLEX REGULAR EXPRESSIONS
# 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$" textfile1.txt </span><br><br>What do you notice?<br><br>Anchoring patterns at both the <u>beginning</u> and <u>ending</u> of strings can greatly assist for more robust search patterns.<br><br>We will now be demonstrating the usefulness of '''simultaneous anchoring''' with other complex regular expressions symbols.<br><br>
# Issue the following command to match strings that begin with 3 characters:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^..." textfile1.txt</span><br><br>What do you notice? Can lines that contain '''less than 3 characters''' be displayed?<br><br>
# Issue the following command to match strings that begin and end with 3 characters:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^...$" textfile1.txt</span><br><br>What do you noticecompared 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>Did only notice lines containing only 3 digits appear?<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]$" textfile1.txt</span><br><br>
# Issue the following command to match strings that consist of only 3 digits:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[0-9][0-9][0-9]$" textfile1.txt</span><br><br>The '''*''' complex regular expression symbol is often confused with filename expansion. In other words, it does NOT represent zero or more of '''any character''', but zero or or occurrences of the character that comes before the * symbol.<br><br>
