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

/
/
gm

Test String

Code Generator

Generated Code

const regex = /(^\s+_[A-Za-z]+\._)/gm; // Alternative syntax using RegExp constructor // const regex = new RegExp('(^\\s+_[A-Za-z]+\\._)', 'gm') const str = `was from an authentic copy, and a careful comparison of the text with the earlier one shows that in the meantime the play "underwent revision, received some slight augmentation, and in some few places must have been entirely rewritten." A marked instance of this rewriting--the only one of considerable length--is in ii. 6. 6-37, where the first quarto reads thus (spelling and pointing being modernized):-- _Jul._ Romeo. _Rom._ My Juliet, welcome. As do waking eyes Closed in Night's mists attend the frolick Day, So Romeo hath expected Juliet, And thou art come. _Jul._ I am, if I be Day, Come to my Sun: shine forth and make me fair. _Rom._ All beauteous fairness dwelleth in thine eyes. _Jul._ Romeo, from thine all brightness doth arise. _Fri._ Come, wantons, come, the stealing hours do pass, Defer embracements till some fitter time. Part for a while, you shall not be alone Till holy Church have joined ye both in one. _Rom._ Lead, holy Father, all delay seems long. _Jul._ Make haste, make haste, this lingering doth us wrong. For convenient comparison I quote the later text here:-- _Juliet._ Good even to my ghostly confessor. _Friar Laurence._ Romeo shall thank thee, daughter, for us both. _Juliet._ As much to him, else is his thanks too much. _Romeo._ Ah, Juliet, if the measure of thy joy Be heap'd like mine and that thy skill be more To blazon it, then sweeten with thy breath This neighbour air, and let rich music's tongue Unfold the imagin'd happiness that both Receive in either by this dear encounter. _Juliet._ Conceit, more rich in matter than in words, Brags of his substance, not of ornament. They are but beggars that can count their worth; But my true love is grown to such excess I cannot sum up half my sum of wealth. _Friar Laurence._ Come, come with me, and we will make short work; For, by your leaves, you shall not stay alone Till holy church incorporate two in one. The "omission, mutilation, or botching" by which some German editors would explain all differences between the earlier and later texts will not suffice to account for such divergence as this. "The two dialogues do not differ merely in expressiveness and effect; they embody different conceptions of the characters;" and yet we cannot doubt that both were written by Shakespeare. `; // Reset `lastIndex` if this regex is defined globally // regex.lastIndex = 0; let m; while ((m = regex.exec(str)) !== null) { // This is necessary to avoid infinite loops with zero-width matches if (m.index === regex.lastIndex) { regex.lastIndex++; } // The result can be accessed through the `m`-variable. m.forEach((match, groupIndex) => { console.log(`Found match, group ${groupIndex}: ${match}`); }); }

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 JavaScript, please visit: https://developer.mozilla.org/en/docs/Web/JavaScript/Guide/Regular_Expressions