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

/
/
g

Test String

Code Generator

Generated Code

const regex = /(\${1,2})[^]*?[^\\]\1|[^\$]+/g; // Alternative syntax using RegExp constructor // const regex = new RegExp('(\\${1,2})[^]*?[^\\\\]\\1|[^\\$]+', 'g') const str = `some text outside \$ \\\$2+\\\$ \$ which includes \$\\\$\$ Now some \$\${}\$\$ \$\\{\\}\$inline mathjax \$2+2\$ And in new lines \$\$ 2+2 \$\$ \$ 2+2\\\\ 3+3\\\\ 4+4\\\\ \$ more inline \$2+2\\\$ \\\$2+2\$ \$2+2\$, \$3+4\$ separated \$2+2\$ by some text \$ 2+2 \$ again double newlines \$2+2\$ \$2+2\$ Dollar again \$ \\\$42 \$ \$\$ \\\$42 \$\$ \$\$ \\frac{4}{2}+ \\frac{4}{2} \$\$ And some more tests: \\> a) \$\\dr{1}{2}+\\left(\\dr23-\\dr34\\right)\$<<< \\> b) \$\\dr{1}{5}+\\left(\\dr23-\\dr12\\right)\$<<< \\> c) \$\\dr{1}{2}+\\left(\\dr{3}{4}-\\dr32\\right)\$<<< \\> d) \$\\left(\\dr{3}{10}-\\dr{5}{2}\\right)+\\dr7{20}\$<<< \\> e) \$\\dr{2}{3}+\\left(\\dr{3}{2}-\\dr14\\right)\$<<< \\> f) \$\\left(\\dr{14}{5}-\\dr7{10}\\right)+\\dr{11}{10}\$.<<< \$\$ a^{\\rr mn}=\\sq[n]{a^m}. \$\$ \$\$ \\begin{align} &a^x\\cdot a^y=a^{x+y}\\\\ &\\dr{a^x}{a^y}=a^{x-y}\\\\ &(a^x)^y=a^{xy}\\\\ &(ab)^x=a^xb^x\\\\ &\\left(\\dr ab\\right)^x=\\dr{a^x}{b^x}. \\end{align} \$\$ \$\$ \\sq[4]{5\\sq5}=(5\\sq5)^{\\rr14}=(5\\.5^{\\rr12})^{\\rr14}= (5^{1+\\rr12})^{\\rr14}=(5^{\\rr32})^{\\rr14}=5^{\\rr38}. \$\$ Hope that's it. `; // 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