Regex Hunter
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Anchors & boundaries

Match positions, not characters — pin your pattern to the start, the end, or the seams between words.

Read the rules: Anchors & boundaries in the Guide →Drill it: Anchor's away →

Builds on Quantifiers

What you'll learn

Start & end Exact length Word boundaries Non-boundaries

Steps · 13

  1. 01Zero-width huntersBriefing
  2. 02Anchored to the startHunt
  3. 03Anchored to the endHunt
  4. 04Both ends — exact matchHunt
  5. 05Exact lengthHunt
  6. 06Counting with bracesHunt
  7. 07Word boundariesHunt
  8. 08Whole word onlyHunt
  9. 09The non-boundaryHunt
  10. 10Starts with a capitalHunt
  11. 11Ends with a digitHunt
  12. 12Golf: ends in "ing"Hunt
  13. 13Positions, masteredBriefing

Regex anchors and word boundaries

Most of a regular expression matches characters: a letter, a digit, a dot. Anchors match a position instead. They sit between characters and use up nothing, so they tell the pattern where it may match, not what it matches.

The two main anchors are ^ for the start of the text and $ for the end. Put ^ in front and the match has to begin at the first character. Put $ at the back and it has to finish at the last one. Use both and the pattern must cover the whole text, which is how you check that an input is exactly a code, a number or a date and nothing more.

A word boundary, \b, is the seam between a word character (a letter, digit or underscore) and anything else, including the edge of the text. It lets you find a whole word without catching it inside longer words. Its opposite, \B, matches wherever \b doesn't, usually inside a word. In a hunt, anchors are often the shortest way to spare words that contain the right letters in the wrong place.

Examples

  1. /^re/

    Catches

    • redo
    • remix
    • return

    Spares

    • fire
    • pure
    • tree

    The caret ties re to the first two letters, so a word that only contains or ends with it is spared.

  2. /^v\d+$/

    Catches

    • v1
    • v12
    • v2026

    Spares

    • v1.2
    • xv1
    • v

    With both anchors, the whole text must be a v and then digits, so a dot, an extra letter in front or a bare v fails the match.

  3. /\bpen\b/

    Catches

    • pen
    • a pen
    • pen pal

    Spares

    • open
    • pencil
    • happen

    Boundaries on both sides find pen as a word of its own and skip it when other letters touch it.

  4. /\Bair\B/

    Catches

    • chairs
    • repairs
    • fairy

    Spares

    • air
    • airy
    • chair

    \B on both sides demands word characters before and after, so air at the start or end of a word is spared.

Common mistakes

  • Anchoring one end only. ^\d+ still matches 12abc because nothing stops the match before the letters; add $ when the whole text must fit.
  • Expecting \b to know every alphabet. In JavaScript only A-Z, a-z, 0-9 and _ are word characters, so \bcaf\b matches inside café, and the hyphen in co-op counts as a boundary.
  • Losing the backslash in a string. Inside a JavaScript string, "\b" is a backspace character, so build the pattern as new RegExp("\\bpen\\b") or write the literal /\bpen\b/.

Read the rules: Anchors & boundaries in the Guide →Drill it: Anchor's away →

Read more: Regex anchors: ^, $ and multiline mode explained →