Some programmers wonder why they even need to learn regular expressions. Here are some use cases:

• While searching for some text at times, there are cases where we don't know the value of the text upfront. We just know some rules or patterns of the text. For example, searching for a MAC address in a log message, searching for IP address in a web server access log, or searching for a 10-digit mobile number that may be optionally preceded by 0 or +<2 digit country code>.
• Sometimes, the length of the text we are trying to extract is unknown, for example, searching URLs that start with http:// or https:// in a CSV file.
• Sometimes, we need to split a given text on delimiters of a variable type and length and generate tokens.
• Sometimes, we need to extract text that falls between two or more search patterns.
• Often, we need to validate the various forms of user inputs, such as bank account number, passwords, usernames, credit card info, phone number, date of birth, and so on.
• There are situations where you only want to capture all the repeated words from a line.
• To convert input text into certain predefined formats, such as inserting a comma after every three digits or removing commas inside parentheses only.
• To do a global search replace while skipping all the escaped characters.