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→INVESTIGATION 2: EXTENDED REGULAR EXPRESSIONS
# 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>
# 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]*$" numbers2.dat | more</span><br><br>You should notice multiple + or - signs are appearing as well. This occurs since you are searching or one or MORE occurrences of a + or - sign.<br>Using '''extended regular expression''' symbols can solve this problem.<br><br>
# Issue the following linux command (using extended regular expression symbols) to display only whole numbers (with or without a positive or negative sign):<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[+-]{0.1}[0-9]{1,}$" numbers2.dat | more</span><br><br>NOTE: most likely, there were NO results. This is due to the fact that the grep command was NOT issued correctly to use extended regular expression symbols. You would need to issue either '''grep -E''' (or more simply) issue the '''egrep''' command. The egrep command works with all regular expression symbols, and should be used in the future instead of the older grep command.<br><br>
# Issue the corrected command:<br><span style="color:blue;font-weight:bold;font-family:courier;">egrep "^[+-]{0,1}[0-9]{1,}$" numbers2.dat | more</span><br><br>Did the command work this time?<br><br>
