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# 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/scriptsmyscripts/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>
: 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>
# Issue the following Linux pipeline command using the repetition shortcuts <span style="font-weight:bold;font-family:courier;">"+"</span> and <span style="font-weight:bold;font-family:courier;">"?"</span>:<br><span style="color:blue;font-weight:bold;font-family:courier;">egrep "^[+-]?[0-9]+$" numbers2.dat | tee better-number2.txt</span><br><br>You should have seen the same results, but the extended regular expression required less typing.<br><br>
# Issue the following Linux pipeline command to display '''signed''', '''unsigned''', '''whole''', and '''decimal''' numbers:<br><span style="color:blue;font-weight:bold;font-family:courier;">egrep "^[+-]{0,1}[0-9]{1,}[.]{0,1}[0-9]*$" numbers2.dat | tee better-number3.txt</span><br><br>Were all signed and unsigned intergers and decimal numbers displayed?<br><br>
# Issue the follwoing command to check that you correctly issued<br>those ''Linux pipeline commands'': <br><span style="color:blue;font-weight:bold;font-family:courier;">bash /home/murray.saul/scriptsmyscripts/week9-check-2</span><br><br>If you encounter errors, then view the feedback to make corrections, and then re-run the checking script.<br>If you receive a congratulation message that there are no errors, then proceed with this tutorial.<br><br>You can also use extended regular expression symbols for '''grouping'''.<br>For example, you can search for repetitions of GROUPS of characters (like a word)<br>as opposed to just a single character or a GROUP of numbers as opposed to a single digit.<br><br>
# Issue the following linux pipeline command to download another data file called '''words.dat''':<br><span style="color:blue;font-weight:bold;font-family:courier;">wget <nowiki>https://ict.senecacollege.ca/~murray.saul/uli101/words.dat</nowiki></span><br><br>
# View the contents of the '''words.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>
# Reissue the previous pipeline command including a space in brackets:<br><span style="color:blue;font-weight:bold;font-family:courier;">egrep -i "(the ){2,}" words.dat | tee word-search2.txt</span><br><br>[[Image:eregexps-3.png|thumb|right|330px|Using '''extended''' regular expression symbols (such as '''grouping''') to refine matches of repetition of '''words''' (as opposed to ''characters'').]]The <span style="font-weight:bold;font-family:courier;">"|"</span> (or) symbol (same symbol as "pipe") can be used within the grouping symbols to allow matching of additional groups of characters.<br>Again, it is important to follow the character groupings with the space character<br><br>
# Issue the following linux pipeline command to search for 2 or more occurrences of the word "'''the '''" <u>or</u> the word "'''and '''":<br><span style="color:blue;font-weight:bold;font-family:courier;">egrep -i "(the |and ){2,}" words.dat | tee word-search3.txt</span><br><br>
# Issue the following Linux command to check that you correctly issued<br>those ''Linux pipeline commands'' using the '''tee''' command to create those text files:<br><span style="color:blue;font-weight:bold;font-family:courier;">bash /home/murray.saul/scriptsmyscripts/week9-check-3</span><br><br>If you encounter errors, then view the feedback to make corrections, and then re-run the checking script.<br>If you receive a congratulation message that there are no errors, then proceed with this tutorial.<br><br>
: The '''grep''' and '''egrep''' Linux commands are NOT the only Linux commands that use regular expressions.<br>In the next investigation, you will apply regular expressions to a number of Linux commands that you already learned in this course.
#Let's learn how to perform a simple '''search and replace''' within the '''vi''' utility by using regular expressions.<br>Issue the following Linux command to edit the '''large-file.txt''' file:<br><span style="color:blue;font-weight:bold;font-family:courier;">vi large-file.txt</span><br><br>Let's first perform a simple search within this text file.<br><br>
# Press the '''ESC''' key to make certain you are in '''COMMAND''' mode.<br><br>
# Type the following and press '''ENTER''':<br><span style="color:blue;font-weight:bold;font-family:courier;">/uli101</span><br><br>You should move to the '''first occurrence''' of the pattern: '''uli101'''.<br><br>Let's search for the '''uli101''' pattern, but replace it in capitals (i.e '''ULI101''').<br><br>In vi, to issue a command, you need to enter '''LAST LINE''' mode then issue a command.<br>Let's issue a command from LAST LINE mode to search and replace '''uli101''' to '''ULI101'''.<br><br>[[Image:other-re-4.png|thumb|right|500px|In l'''ast line''' MODE in the '''vi''' text editor, issuing a command using regular expressions to convert '''uli101''' to '''ULI101'''.]]
# Making certain that you are command mode in vi, type the following and press ENTER:<br><span style="color:blue;font-weight:bold;font-family:courier;">:%s/uli101/ULI101/g</span><br><br>
# Navigate throughout the text file to confirm that ALL occurrences of uli101 have been replaced with ULI101.<br><br>
