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

Substitution

Processing...

Code Generator

Language

Generated Code

const regex = new RegExp('<span class="italics">([^<]*?)</span>', 'g') const str = `What I am trying to do is to change all instances of <span class="italics">italicised text here</span> to <em>italicised text here</em> where the text in the middle changes throughout the document. I can't just find replace, because there are 598 instances of <span class="italics">, and 700 cases of </span>. Also, I want to learn how to do the find replace with leaving the stuff in the middle alone. Do I use (.+?) at some point? I've been googling but unable to figure it out. Thank you in advance for your help! Okay, your string finds the 598 I need to replace in my document, what can I add to the ([\\S\\s]*?) to get it to replace the span tags and leave the text between the span tags alone? For example, if it's <span class="italics">The New York Times</span> and <span class="italics">The Hitchhiker's Guide to the Galaxy</span>, is it possible to change those to <em">The New York Times</em> and <em>The Hitchhiker's Guide to the Galaxy</em> in one go, or do I have to do them individually?`; const subst = `<em>\1</em>`; // The substituted value will be contained in the result variable const result = str.replace(regex, subst); console.log('Substitution result: ', result);

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