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→INVESTIGATION 3: OTHER COMMANDS THAT USE REGULAR EXPRESSIONS
= INVESTIGATION 3: OTHER COMMANDS THAT USE REGULAR EXPRESSIONS =
In this investigation, you will see commands other than '''grep''' or '''egrep''' that can use regular expressions.
'''Perform the Following Steps:'''
# Make certain that you are located in your '''~/regexps''' directory on your ''Matrix'' account.<br><br>
# Let's look at using regular expressions with the '''man''' command.<br>Issue the following linux command :<br><span style="color:blue;font-weight:bold;font-family:courier;">man ls</span><br><br>[[Image:other-re-1.png|thumb|right|300px|Entering '''/sort''' in the '''man''' command can search for the string "'''sort'''".]]
# We want to search for an option that can sort the file listing.<br>Type the following regular expression below and press '''ENTER''':<br><span style="color:blue;font-weight:bold;font-family:courier;">/sort</span><br><br>'''FYI:''' The '''grep''' and '''egrep''' Linux commands contain the regular expressions within quotes, but '''most''' other Linux commands specify regular expressions using<br>'''forward slashes''' (e.g. <span style="font-weight:bold;font-family:courier;">/regular expression</span> or <span style="font-weight:bold;font-family:courier;">/regular expression/</span>).<br><br>
# Scroll throughout the man pages for the ls command to view matches for the pattern "'''sort'''"<br>(You can press '''SPACE''' or key combination '''alt-b''' to move forward and backwards one screen respectively).<br><br>
# Press the letter <span style="color:blue;font-weight:bold;font-family:courier;">q</span> to '''exit''' the ''man'' pages for '''ls'''.<br><br>Let's use regular expressions with the '''less''' command.<br><br>
# Issue the following Linux command to download another data file called '''large-file.txt''':<br><span style="color:blue;font-weight:bold;font-family:courier;">wget <nowiki>https://ict.senecacollege.ca/~murray.saul/uli101/large-file.txt</nowiki></span><br><br>[[Image:other-re-2.png|thumb|right|300px|Entering '''/uli101''' in the '''less''' command can display all matches of "'''uli101'''" throughout the text file.]]
# Issue the following Linux command to view the contents of the '''large-file.txt''':<br><span style="color:blue;font-weight:bold;font-family:courier;">less large-file.txt</span><br><br>
#We want to search for a pattern '''uli101''' within this text file.<br>Type the following regular expression and press ENTER:<br><span style="color:blue;font-weight:bold;font-family:courier;">/uli101</span><br><br>You should see the pattern "uli101" throughout the text file.<br><br>
# Press the letter <span style="color:blue;font-weight:bold;font-family:courier;">q</span> to exit the '''less''' command.<br><br>
# Try the same search techniques with the '''more''' command.<br><br>Does it work the same for the ''less'' command?<br><br>[[Image:other-re-3.png|thumb|right|300px|Entering '''/uli101''' in the '''vi''' command can search for the string "'''uli101'''".]]Let's learn how to perform a simple '''search and replace''' within the '''vi''' utility<br>by using regular expressions.<br><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 notice the pattern "'''uli101'''" highlighted for ALL occurrences in this text file.<br><br>Let's '''search''' for the '''uli101''' pattern, and '''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,<br>type the following and press '''ENTER''':<br><span style="color:blue;font-weight:bold;font-family:courier;">:%s/uli101/ULI101/g</span><br><br>'''NOTE:''' The letter '''g''' after the replace regular expression represents "'''global'''" and will replace ALL occurrences of uli101 in the text document (as opposed to replacing the first occurrence for every line).<br><br>
# Type the following (in uppercase letters) and press '''ENTER''':<br><span style="color:blue;font-weight:bold;font-family:courier;">/ULI101</span><br><br>You should notice the pattern "'''ULI101'''" highlighted for ALL occurrences in this text file.<br><br>
# Navigate throughout the text file to confirm that ALL occurrences of '''uli101''' have been <u>replaced</u> with '''ULI101'''.<br><br>
# Save changes to your vi editing session and exit by typing the following and pressing ENTER:<br><span style="color:blue;font-weight:bold;font-family:courier;">:x</span><br><br>
: After you complete the '''Review Questions''' section to get additional practice.
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= LINUX PRACTICE QUESTIONS =