Reading 03: Filtering Text

Readings

The readings for Monday, February 6 are:

1. The Linux Command Line:

   • Chapter 19 - Regular Expressions
   • Chapter 20 - Text Processing

2. RegexOne

   Work through the Lessons in the Interactive Tutorial.

Optional Resources:

• Linux Command Line Tutorial - Regular Expressions

• Regular Expressions - User Guide

• Digital Ocean Tutorials:

  • Using Grep & Regular Expressions to Search for Text Patterns in Linux

  • The Basics of Using the Sed Stream Editor to Manipulate Text in Linux

• Advanced Bash Scripting - Text Processing Commands

• The Unix School - Awk & Sed

• Sed - An Introduction and Tutorial

• Grep - An introduction to grep and egrep

• USEFUL ONE-LINE SCRIPTS FOR SED

Questions

In your reading03/README.md file, describe what command(s) you would use to accomplish the following:

1. Convert all the input text to upper case:

   $ echo "All your base are belong to us" | ...
   ALL YOUR BASE ARE BELONG TO US
   

2. Find and replace all instances of monkeys to gorillaz:

   $ echo "monkeys love bananas" | ...
   gorillaz love bananas
   

3. Remove any leading whitespace from a string of text:

   $ echo "     monkeys love bananas" | ...
   monkeys love bananas
   

4. Parse the /etc/passwd file for the shell of the root user:

   $ cat /etc/passwd | ...
   /bin/bash
   

   Hint: You may need to read up on the format of /etc/passwd

5. Find and replace all instances of /bin/bash, /bin/csh, and /bin/tcsh to /usr/bin/python in /etc/passwd:

   $ cat /etc/passwd | ... | grep python
   root:x:0:0:root:/root:/usr/bin/python
   mysql:x:27:27:MySQL Server:/var/lib/mysql:/usr/bin/python
   xguest:x:500:501:Guest:/home/xguest:/usr/bin/python
   condor:x:108172:40:Condor Batch System:/afs/nd.edu/user37/condor:/usr/bin/python
   lukew:x:522:40:Luke Westby temp access:/var/tmp/lukew:/usr/bin/python
   

6. Find all the records in /etc/passwd that have a number that begins with a 4 and ends with a 7:

   $ cat /etc/passwd | ...
   rtkit:x:499:497:RealtimeKit:/proc:/sbin/nologin
   qpidd:x:497:495:Owner of Qpidd Daemons:/var/lib/qpidd:/sbin/nologin
   uuidd:x:495:487:UUID generator helper daemon:/var/lib/libuuid:/sbin/nologin
   mailnull:x:47:47::/var/spool/mqueue:/sbin/nologin
   

7. Given two text files, show all the lines that are present in both files.

8. Given two text files, show which lines are different.

Feedback

If you have any questions, comments, or concerns regarding the course, please provide your feedback at the end of your response.

Submission

To submit your assignment, please commit your work to the reading03 folder in your assignments GitLab repository:

$ cd path/to/repository                   # Go to assignments repository
$ cd reading03                            # Go to reading directory
...
$ $EDITOR README.md                       # Edit README.md
$ git add README.md                       # Mark changes for commit
$ git commit -m "reading03: README.md"    # Record changes
...
$ git push                                # Send changes to GitLab