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
Processing...

Test String

Substitution
Processing...

Code Generator

Language

Generated Code

const regex = /\n(?=\d{4}-)/gm; // Alternative syntax using RegExp constructor // const regex = new RegExp('\\n(?=\\d{4}-)', 'gm') const str = `2022-09-21 05:45:24.8603 Debug Sensor SetState Started 2022-09-21 05:45:26.7529 Info Updater SensorDeploymentLogs no value returned from SensorDeployment 2022-09-21 12:37:47.1286 Error TaskAwaiter RunPeriodic <RegisterPeriodicTask>b__1 failed System.Threading.Tasks.TaskCanceledException: A task was canceled. at async Task<HttpResponseMessage> System.Net.Http.HttpClient.FinishSendAsyncBuffered(Task<HttpResponseMessage> sendTask, HttpRequestMessage request, CancellationTokenSource cts, bool disposeCts) at async Task<TResponse> Microsoft.CommunicationWebClient.SendAsync<TResponse>(byte[] requestBytes, int offset, int count) at async Task<TResponse> Microsoft.CommunicationWebClient.SendWithRetryAsync<TResponse>(byte[] requestBytes, int offset, int count) at async Task<TResponse> Microsoft.CommunicationWebClient.SendAsync<TResponse>(IRequestWithResponse<TResponse> request) at async Task<TResponse> 2022-09-21 12:42:53.2810 Info Updater Sensor no value returned from SensorDeployment`; const subst = `\n--- SPLIT ---\n`; // 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