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→INVESTIGATION 2: EXTENDED REGULAR EXPRESSIONS
# Make certain that you are located in your '''~/regexps''' directory on your ''Matrix'' account.<br><br>
# Issue the following Linux command to download another data file called '''numbers2.dat''':<br><span style="color:blue;font-weight:bold;font-family:courier;">wget <nowiki>https://ict.senecacollege.ca/~murray.saul/uli101/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 more 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 only whole numbers (with or without a positive or negative sign):<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[+-]*[0-9][0-9]*$" numbers2.dat</span><br><br>You should notice '''multiple''' '''+''' or '''-''' '''signs''' appear <u>prior</u> to some numbers.<br>This occurs since you are searching or one or MORE occurrences of a + or - sign.<br><br>Using '''extended regular expression''' symbols to specify '''minimum''' and '''maximum''' repetitions: '''{min,max}''' can solve that problem.<br><br>
# Issue the following Linux command (using extended regular expression symbols)<br>to display only whole numbers (with or without a positive or negative sign):<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[+-]{0.1}[0-9]{1,}$" numbers2.dat</span><br><br>'''NOTE:''' most likely, there were '''NO results'''.<br><br>This is due to the fact that the '''grep command was NOT issued correctly to use extended regular expression symbols'''.<br>You would need to issue either '''grep -E''' (or more simply) issue the '''egrep''' command. The egrep command works with<br>'''all''' regular expression symbols, and should be used in the future instead of the older grep command.<br><br>
