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Tutorial 9 - Regular Expressions

306 bytes removed, 21:30, 25 October 2021

→‎INVESTIGATION 1: SIMPLE & COMPLEX REGULAR EXPRESSIONS

# '''Login''' to your matrix account.

# Issue a Linux command to '''confirm''' you are located in your '''home''' directory. The '''wget''' command is used to download files from the Internet to your shell. This will be useful to download '''text files''' and '''data files''' that we will be using in this tutorial. # Issue the following linux Linux command to '''~~download~~copy''' a text file to your '''home''' directory: ~~wget <nowiki>https://ict.senecacollege.ca/~~cp ~~~murray.saul~~osl640/~~uli101~~tutorial9/textfile1.txt~~</nowiki>~~.

# View the contents of the '''textfile1.txt''' file using the '''more''' command see what data is contained in this file. Although there are several Linux commands that use regular expressions, we will be using the '''grep''' command for this investigation. [[Image:regexps-1.png|thumb|right|250px|Output of '''grep''' command matching simple regular expression "'''the'''" (only lowercase). Notice the pattern matches larger words like "'''their'''" or "'''them'''".]]

#Issue the following Linux command to match the pattern '''the''' within '''textfile1.txt''': grep "the" textfile1.txt Take a few moments to view the output and observe the matched patterns.

# Issue the following Linux command to create the '''regexps''' directory: mkdir ~/regexps

# Change to the '''regexps''' directory and confirm that you have moved to this directory.

# First, issue the following Linux command to ~~download~~ copy another data file called '''numbers1.dat''': ~~wget <nowiki>https://ict.senecacollege.ca/~~cp ~~~murray.saul~~osl640/~~uli101~~tutorial9/numbers1.dat~~</nowiki>~~.

# View the contents of the '''numbers.dat''' file using the '''more''' command and quickly view the contents of this file. You should notice '''valid''' and '''invalid''' numbers contained in this file. When finished, exit the more command.

# Issue the following linux pipeline command to display only '''whole''' numbers (i.e. no '''+''' or '''-''' sign): grep "^[0-9]*$" numbers1.dat | tee faulty.txt You may have noticed that the command '''does not entirely work'''. You may notice an '''empty line''' (which is NOT a whole number). This occurs since the * regular expression symbol represents ZERO or MORE occurrences of a number. You can use an additional numeric character class with the * regular expression symbol to search for one or more occurrences of a number.

# Issue the following Linux pipeline command to display only '''signed''' integers: grep "^[+-][0-9][0-9]*$" numbers1.dat | tee signed.txt What did you notice? Positive and negative numbers display, not '''unsigned''' numbers. [[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 '''signed''' or '''unsigned integers''': grep "^[+-]*[0-9][0-9]*$" numbers1.dat | tee all.txt Did this command work?

# Issue the following command to check that you created those hard links: ~~~uli101~~osl640/week9-check-1 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. You can also use the '''grep''' command using ''regular expression'' as a '''filter''' in pipeline commands.

# Issue the following Linux pipeline command: ls | grep "[0-9].*dat$" What did this pipeline display?

# Issue the following Linux pipeline command: ls | grep "[a-z].*txt$" What did this pipeline display?

Jason Michael Carman

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Tutorial 9 - Regular Expressions

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