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Test regular expressions with real-time matching, flags, and highlighted results.
A regular expression is a sequence of characters that defines a search pattern for matching, finding, and replacing text. Regex is used in programming, text editors, and command-line tools for pattern-based string operations.
g=global, i=case-insensitive, m=multiline, s=dotall, u=unicode
\d+).. Any character\d Digit [0-9]\w Word char\s Whitespace^ Start of line$ End of line* 0 or more+ 1 or more? 0 or 1{n} Exactly n[abc] Character set(group) CaptureFormula
/pattern/flags → match array | nullpattern = Sequence of characters and metacharacters defining the search
flags = Modifiers: g (global), i (case-insensitive), m (multiline), s (dotall), u (unicode)
match array = Array of matched strings; null if no match found
Worked Example
Match all email addresses
Did you know? Regular expressions were invented by mathematician Stephen Cole Kleene in 1951 as a notation for regular languages in automata theory. Ken Thompson later implemented them in the QED text editor (1968), which became the ancestor of grep and modern regex engines.
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