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Tutorial9: Regular Expressions

7 bytes added, 12:58, 14 July 2023
INVESTIGATION 1: SIMPLE & COMPLEX REGULAR EXPRESSIONS
# Issue the following Linux command to create the '''regexps''' directory: <span style="color:blue;font-weight:bold;font-family:courier;">mkdir ~/regexps</span><br><br>
# Change to the '''regexps''' directory and confirm that you have moved to this directory.<br><br>
# First, issue the following Linux command to copy another data file called '''numbers1.dat''':<br><span style="color:blue;font-weight:bold;font-family:courier;">cp ~uli101/tutorialfiles/numbers1.dat ~/regexps</span><br><br>
# View the contents of the '''numbers.dat''' file using the '''more''' command and quickly view the contents of this file.<br>You should notice '''valid''' and '''invalid''' numbers contained in this file. When finished, exit the more command.<br><br>
# Issue the following linux pipeline command to display only '''whole''' numbers (i.e. no '''+''' or '''-''' sign):<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "^[0-9]*$" numbers1.dat | tee faulty.txt</span><br><br>You may have noticed that the command '''does not entirely work'''. You may notice an '''empty line'''<br>(which is NOT a whole number). This occurs since the * regular expression symbol represents<br>ZERO or MORE occurrences of a number. You can use an additional numeric character class<br>with the * regular expression symbol to search for one or more occurrences of a number.<br><br>

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