Renowned mathematician Stephen Kleene built a model in the year 1956 using finite automata for simple algebra. He described regular languages using his mathematical notation called regular sets. Computer programmers started using regular expressions in the 1970s when the Unix operating system and some of its text editors and text processing utilities such as ed, sed, emacs, lex, vi, grep, awk, and so on were built. Regular expressions gained more popularity with the arrival of Perl and Tcl scripting languages in the 1980s and 1990s. Since then, all the popular programming languages, such as Java, Python, Ruby, R, PHP, and .NET have built very good support of regular expressions.
- Preface
- Getting Started with Regular Expressions
- Introduction to regular expressions
- Summary
- Understanding the Core Constructs of Java Regular Expressions
- Understanding the core constructs of regular expressions
- Quantifiers
- Basic quantifiers
- Greedy versus reluctant (lazy) matching using quantifiers
- Possessive quantifiers
- Boundary constructs
- Character classes
- Escaping special regex metacharacters and escaping rules inside the character classes
- Predefined shorthand character classes
- Unicode support in Java regular expressions
- Commonly used Unicode character properties
- Negation of the preceding regex directives
- Unicode scripts support
- Double escaping in a Java String when defining regular expressions
- Embedded regular expression mode modifiers
- The placement of embedded modes in a Java regular expression
- Disabling mode modifiers
- Summary
- Working with Groups, Capturing, and References
- Regular Expression Programming Using Java String and Scanner APIs
- Introduction to the Java String API for regular expressions' evaluation
- Using regular expressions in Java Scanner API
- Summary
- Introduction to Java Regular Expression APIs - Pattern and Matcher Classes
- Exploring Zero-Width Assertions, Lookarounds, and Atomic Groups
- Understanding the Union, Intersection, and Subtraction of Character Classes
- Regular Expression Pitfalls, Optimization, and Performance Improvements
- Common pitfalls and ways to avoid them while writing regular expressions
- Do not forget to escape regex metacharacters outside a character class
- Avoid escaping every non-word character
- Avoid unnecessary capturing groups to reduce memory consumption
- However, don't forget to use the required group around alternation
- Use predefined character classes instead of longer versions
- Use the limiting quantifier instead of repeating a character or pattern multiple times
- Do not use an unescaped hyphen in the middle of a character class
- The mistake of calling matcher.goup() without a prior call to matcher.find(), matcher.matches(), or matcher.lookingAt()
- Do not use regular expressions to parse XML / HTML data
- How to test and benchmark your regular expression performance
- Catastrophic or exponential backtracking
- Optimization and performance enhancement tips
- Use a compiled form of regular expressions
- Use a negated character class instead of the greedy and slow .* or .+
- Avoid unnecessary grouping
- Use lazy quantifiers strategically instead of greedy quantifiers that cause excessive backtracking
- Make use of possessive quantifiers to avoid backtracking
- Extract common repeating substrings out of alternation
- Use atomic group to avoid backtracking and fail fast
- Summary
- Common pitfalls and ways to avoid them while writing regular expressions
A bit of history of regular expressions
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