Regular Expressions 101

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An explanation of your regex will be automatically generated as you type.
Detailed match information will be displayed here automatically.
  • All Tokens
  • Common Tokens
  • General Tokens
  • Anchors
  • Meta Sequences
  • Quantifiers
  • Group Constructs
  • Character Classes
  • Flags/Modifiers
  • Substitution
  • A single character of: a, b or c
    [abc]
  • A character except: a, b or c
    [^abc]
  • A character in the range: a-z
    [a-z]
  • A character not in the range: a-z
    [^a-z]
  • A character in the range: a-z or A-Z
    [a-zA-Z]
  • Any single character
    .
  • Alternate - match either a or b
    a|b
  • Any whitespace character
    \s
  • Any non-whitespace character
    \S
  • Any digit
    \d
  • Any non-digit
    \D
  • Any word character
    \w
  • Any non-word character
    \W
  • Non-capturing group
    (?:...)
  • Capturing group
    (...)
  • Zero or one of a
    a?
  • Zero or more of a
    a*
  • One or more of a
    a+
  • Exactly 3 of a
    a{3}
  • 3 or more of a
    a{3,}
  • Between 3 and 6 of a
    a{3,6}
  • Start of string
    ^
  • End of string
    $
  • A word boundary
    \b
  • Non-word boundary
    \B

Regular Expression
No Match

/
/

Test String

Code Generator

Generated Code

// include the latest version of the regex crate in your Cargo.toml extern crate regex; use regex::Regex; fn main() { let regex = Regex::new(r"^function (\w+)\(").unwrap(); let string = "function Date(Y, M, D, h, m, s, ms) { // 1397 var length = arguments.length; // 1398 var date; // 1399 if (this instanceof NativeDate) { // 1400 var seconds = s; // 1401 var millis = ms; // 1402 if (hasSafariSignedIntBug && length >= 7 && ms > maxSafeUnsigned32Bit) { // 1403 // work around a Safari 8/9 bug where it treats the seconds as signed // 1404 var msToShift = Math.floor(ms / maxSafeUnsigned32Bit) * maxSafeUnsigned32Bit; // 1405 var sToShift = Math.floor(msToShift / 1e3); // 1406 seconds += sToShift; // 1407 millis -= sToShift * 1e3; // 1408 } // 1409 date = length === 1 && $String(Y) === Y ? // isString(Y) // 1410 // We explicitly pass it through parse: // 1411 new NativeDate(DateShim.parse(Y)) : // 1412 // We have to manually make calls depending on argument // 1413 // length here // 1414 length >= 7 ? new NativeDate(Y, M, D, h, m, seconds, millis) : // 1415 length >= 6 ? new NativeDate(Y, M, D, h, m, seconds) : // 1416 length >= 5 ? new NativeDate(Y, M, D, h, m) : // 1417 length >= 4 ? new NativeDate(Y, M, D, h) : // 1418 length >= 3 ? new NativeDate(Y, M, D) : // 1419 length >= 2 ? new NativeDate(Y, M) : // 1420 length >= 1 ? new NativeDate(Y instanceof NativeDate ? +Y : Y) : // 1421 new NativeDate(); // 1422 } else { // 1423 date = NativeDate.apply(this, arguments); // 1424 } // 1425 if (!isPrimitive(date)) { // 1426 // Prevent mixups with unfixed Date object // 1427 defineProperties(date, { constructor: DateShim }, true); // 1428 } // 1429 return date; // 1430 }"; // result will be a tuple containing the start and end indices for the first match in the string let result = regex.captures(string); let (start, end) = match result { Some((s, e)) => (s, e), None => { // ... } }; println!("{}", &string[start, end]); }

Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Rust, please visit: https://docs.rs/regex/latest/regex/