Discuss advanced techniques for working with regular expressions in Perl.

When working with regular expressions in Perl, there are several advanced techniques and features that can greatly expand your capabilities and allow you to handle complex pattern matching tasks. Here are some advanced techniques for working with regular expressions in Perl:

1. Anchors:

* Anchors are special characters that match a specific position within a string.
* The caret (^) anchor matches the beginning of a line or string.
* The dollar ($) anchor matches the end of a line or string.
* Anchors are useful for ensuring that a pattern matches only at specific positions within the input.
* Example: `/^start/` matches "start" only if it occurs at the beginning of a line or string.
2. Word Boundaries:

* The \b metacharacter represents a word boundary.
* It matches the position between a word character (\w) and a non-word character (\W).
* Word boundaries are helpful for matching whole words rather than partial matches.
* Example: `/\bword\b/` matches the word "word" as a whole word, not as part of another word.
3. Capture Groups and Backreferences:

* Capture groups, denoted by parentheses (), allow you to capture and store parts of a matched pattern for later use.
* Backreferences, represented by $1, $2, etc., refer to the captured substrings.
* They enable you to reuse and manipulate specific parts of a match within the same regular expression or in replacement strings.
* Example: `/(abc)(def)\1\2/` matches "abcdefabcdef" and utilizes capture groups for repetition.
4. Quantifiers:

* Quantifiers allow you to specify the number of times a pattern should repeat.
* The asterisk () matches zero or more occurrences of the preceding pattern.
* The plus sign (+) matches one or more occurrences.
* The question mark (?) matches zero or one occurrence.
* Curly braces ({}) allow you to specify a specific range or exact number of occurrences.
* Quantifiers provide flexibility in matching patterns with varying repetition.
* Example: `/a{2,4}/` matches "aa", "aaa", or "aaaa".
5. Lookahead and Lookbehind Assertions:

* Lookahead (?=pattern) and lookbehind (?<=pattern) assertions allow you to match patterns based on what precedes or follows the current position.
* They are non-capturing and only check for the existence or absence of a pattern without including it in the match.
* Lookahead assertions enable you to match patterns based on specific conditions.
* Example: `/(\d+)(?=[a-z]+)/` matches one or more digits only if they are followed by lowercase letters.
6. Modifiers:

* Perl provides several modifiers that affect the behavior of regular expressions.
* The /i modifier makes the matching case-insensitive.
* The /m modifier allows ^ and $ to match the beginning and end of lines (instead of the whole string).
* The /s modifier allows the dot (.) to match newline characters.
* Modifiers allow you to customize how patterns are matched and enhance the flexibility of regular expressions.
7. Advanced Character Classes:

* Perl supports advanced character classes for more specific matching.
* \d matches any digit (equivalent to [0-9]).
* \D matches any non-digit character.
* \s matches any whitespace character.
* \S matches any non-whitespace character.
* \w matches any word character (alphanumeric or underscore).
* \W matches any non-word character.
* Advanced character classes provide shortcuts for common matching requirements.

These advanced techniques and features in Perl's regular