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→INVESTIGATION 1: SIMPLE & COMPLEX REGULAR EXPRESSIONS
#Issue the following linux pipeline command to match the pattern the within '''textfile1.txt''':<br><span style="color:blue;font-weight:bold;font-family:courier;">grep "the" textfile1.txt</span><br><br>Take a few moments to view the output and observe the matched pattern.<br><br>
# Now, issue the grep linux pipeline command with the '''-i''' option to ignore case sensitively:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep -i "the" textfile1.txt</span><br><br>What do you notice is different with this pipeline command?<br><br>You will notice that the pattern "'''the'''" is matched including larger words like "'''them'''" and "'''their'''".<br>You can issue the '''grep''' command with the -w option to only match the pattern as a '''word'''.<br><br>
# Issue the following linux pipeline command:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep -w -i "the" textfile1.txt</span><br><br>You should now see only strings of text that match the word '''"the"''' (upper or lower case).<br><br>Matching literal or simple regular expressions can be useful, but are '''limited'''<br>in what they can assist with pattern matching. For example, you may want to<br>search for a pattern located at the '''beginning''' or '''end''' of the string.<br><br>There are other regular expression symbols that provide more '''precise''' pattern matches.<br>These special characters are known as '''complex''' and '''extended''' regular expressions symbols.<br> In this section, we will focus on '''complex regular expressions''' and then discuss <br>''extended regular expressions''' in '''investigation 2'''.<br><br>
# Issue the following Linux pipeline command:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep -w -i "^the" textfile1.txt</span><br><br>The '''^''' symbol is an anchor. In this case, it only matches the <u>word</u> "the" (both upper or lowercase) at the beginning of strings.<br>The '''$''' symbol is used to anchor patterns at the end of strings.<br><br>
# Issue the following Linux pipeline command:<br><span style="color:blue;font-weight:bold;font-family:courier;">grep -w -i "the$" textfile1.txt</span><br><br>What do you notice?<br><br>
