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→INVESTIGATION 1: SIMPLE & COMPLEX REGULAR EXPRESSIONS
# Issue the following Linux pipeline command to display whole positive or negative integers:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[+-][0-9][0-9]*$" numbers1.dat | tee signed.txt</span><br><br>What did you notice? Positive and negative numbers display, not not '''unsigned''' numbers.<br><br>[[Image:regexps-8.png|thumb|right|300px|Simultaneous '''anchoring''' of regular expressions using '''character class''' and '''zero or more occurrences''' to display '''signed''' and '''unsigned''' integers.]]
# Issue the following Linux pipeline command to display only whole numbers<br>(with or without a positive or negative sign):<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[+-]*[0-9][0-9]*$" numbers1.dat | tee all.txt</span><br><br>Did this command work?<br><br>
# Issue the following command to check that you created those hard links: <br><span style="color:blue;font-weight:bold;font-family:courier;">bash /home/murray.saul/myscripts/week9-check-1</span><br><br>If you encounter errors, then view the feedback to make corrections, and then re-run the checking script. If you receive a congratulation message that there are no errors, then proceed with this tutorial.<br><br>You can also use the '''grep''' command using ''regular expression'' as a '''filter''' in pipeline commands.<br><br># Issue the following Linux pipeline command:<br><span style="color:blue;font-weight:bold;font-family:courier;">ls | grep "[1-5].*txt$" numbers1.dat | tee signed.txt</span><br><br>What did this pipeline display?<br><br>
: Although very useful, '''complex''' regular expressions do NOT entirely solve our problem of displaying only '''valid''' unsigned and signed numbers.<br>In the next investigation, you will learn how to use '''extended''' regular expressions that will completely solve this issue.<br>