UNIX

Regular expressions are a powerful tool for text processing and pattern matching. They provide a concise way to search, match, and manipulate text data in a variety of applications. In regular expressions, a pattern is defined using a specific syntax and is used to match against text data. The first part of using regular expressions is learning the syntax and understanding the different features and options that can be used to define patterns. The second part involves applying these patterns to text data to search, match, and manipulate the data as needed. Regular expressions are a valuable asset for any individual or organization that works with large amounts of text data, and with the right understanding and practice, they can be used effectively to streamline text processing tasks.

Part A: Learning the Regular Expression Syntax

Then please follow the steps to learn how to edit a small file via vi, grep, egrep.

Before you start, use vi to write the following text to file.txt:

Hello World

Hello, how are you today?

This is a simple test

(1) Search for lines containing the word "Hello" in file.txt.

egrep "Hello" file.txt

grep -E "Hello" file.txt

Search for all instances of the word "Hello" or "World" in the current file in vi.

Open the file with vi, then type the following:

/\(Hello\|World\)

Search for all instances of the word "Hello" at the beginning of a line in the current file in vi:

Question : what command you should use

Search for lines ending with the word "Hello" in file.txt:

grep -E "Hello$" file.txt

Question: Attach screenshot of all the above.

Part B: Extract phone number from a file.

Use vi to write the following content to file phone_numbers.txt.

John: 123-456-7890

Jane: (555) 555-5555

Bob: 555-555-5555

The following grep command will extract all the phone numbers from the text file:.

grep -Eo '[0-9]{3}-[0-9]{3}-[0-9]{4}|\([0-9]{3}\)\ [0-9]{3}-[0-9]{4}' phone_numbers.txt

- Question : Attach screenshot of above.

Part C: Create your regex.

(1) Given a text file that contains a list of URLs, write a grep command that can extract only valid URLs from the file. A valid URL should start with http:// or https://, followed by one or more word characters (letters and numbers), and end with a .com, .org, .net, or .edu extension..

Question : what command you should use

Given a text file that contains a list of email addresses, write a grep command that can extract only valid email addresses from the file. A valid email address should contain a word character, followed by an @ symbol, then another word character, followed by a ., and ending with a two to six letter word character.

Question : what command you should use

Hint: you can use grep -E "Your regex" text_file.txt

You can create a file with the following content to test your command:

http://google.com

https://yahoo.org

https://abc.com

ABC(at)hmail.com

abc.def(at)hawtmail.com

invalid_email