In PHP regular expressions, how can you extract the domain abc.com from the string https://info@abc.com?

Introduction / Context:
String processing and regular expressions are very common tasks in PHP applications, especially for validating and parsing email addresses, URLs, and log lines. Extracting a domain name from a mixed string that contains protocol and user information is a typical example. Interview questions like this check whether the candidate understands how to build capturing groups with preg_match() and how to use character classes to capture only the needed portion.

Given Data / Assumptions:

• The input string looks like https://info@abc.com and contains a protocol prefix, a user part, and a domain part.
• We want to extract the domain abc.com, which appears after the @ symbol.
• We are allowed to use PHP regular expression functions such as preg_match().
• The question focuses on the idea of using a capturing group to isolate the domain portion.

Concept / Approach:
The core idea is to design a regular expression that looks for the @ character and then captures everything that follows up to a delimiter such as a slash or the end of the string. In PHP, preg_match() can apply this pattern to the string and return matches in an array, where the first capturing group contains the domain. The exact pattern can vary, but it generally uses a group with a character class that excludes slashes or whitespace, ensuring that only the domain name is captured. This approach is efficient and avoids complex manual parsing.

Step-by-Step Solution:
Step 1: Identify that the domain we want begins immediately after the @ symbol in the string https://info@abc.com. Step 2: Construct a regular expression that matches the @ symbol and then captures one or more characters that are not slashes or spaces, for example /@([^\\/]+)/. Step 3: In this pattern, @ matches the literal at symbol, and the group ([^\\/]+) captures one or more characters that are not a slash or backslash, which in the example corresponds to abc.com. Step 4: Call preg_match($pattern, $string, $matches) in PHP, where $pattern is the chosen regular expression and $string is the full input. Step 5: After a successful match, $matches[1] contains the value abc.com, which is the domain we wanted to extract. Step 6: This demonstrates a general strategy for extracting domains from similar strings using capturing groups in PHP regular expressions.

Verification / Alternative check:
You can test this approach by running a short PHP script that defines $string as https://info@abc.com, applies preg_match(), and prints $matches[1]. The result should be abc.com. Trying the same pattern on other strings that follow a similar structure confirms that the capturing group isolates the domain part. Minor adjustments to the pattern can handle more complex cases, but the underlying method remains the same.

Why Other Options Are Wrong:
Option b is wrong because md5() produces a one way hash; it cannot be reversed to obtain the domain. Option c is incorrect because exploding on every character and manually rebuilding the domain is unnecessary and fragile compared to using regex or string functions. Option d is wrong because PHP does not provide a built in get_domain() function that automatically extracts domains from arbitrary strings.

Common Pitfalls:
A common pitfall is writing overly strict or overly loose patterns that fail on valid inputs or match too much. Another issue is forgetting to escape special characters like the slash in regular expressions. When working with user provided URLs or email addresses, developers should also consider validation and normalisation rather than relying on simple splits. Nonetheless, understanding how to use preg_match() with capturing groups is a fundamental skill, and extracting abc.com from https://info@abc.com is a straightforward example.

Final Answer:
You can extract abc.com by using preg_match() with a pattern that matches @ and captures the following characters into a group, for example /@([^\\/]+)/, then reading the first capturing group from the matches array.