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

/
/
gmx

Test String

Substitution

Processing...

Code Generator

Language

Generated Code

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Example { public static void main(String[] args) { final String regex = "([ :]) # look for : and space as possible leading characters\n" + "([\\\"]?) # if there's a quote, disregard it\n" + "([0-9]{4}) # find the year\n" + "- # find the 1st dash\n" + "( # Group (4)\n" + " (\n" + " ((0[13578] | (10|12)) # look for 31 day months\n" + " - # followed by the 2nd dash\n" + " (0[1-9]|[1-2][0-9]|3[0-1]) # and accept days up to 31\n" + " ) \n" + " | # OR... \n" + " (02 # look for Feb\n" + " - # followed by the 2nd dash\n" + " (0[1-9]|[1-2][0-9])) # and accept up to 29 days\n" + " | # OR...\n" + " ((0[469]|11)) # look for 30 day months\n" + " - # followed by the 2nd dash\n" + " ((0[1-9]|[1-2][0-9]|30)) # and accept up to 30 days\n" + " )\n" + ") # closes (4)\n" + "([\\\"]?)([ \\\"]?)(\\s)"; final String string = "This regex changes YYYY-MM-DD to \"[[YYYY-MM-DD]]\" for Obsidian\n" + "WORKS ON:\n" + "today: 2025-03-14\n" + "birthdays: 1966-06-19\n" + "Good Dates: 2022-12-31 and 2025-02-08\n" + "old-dates: 1492-01-01 old dates could be an issue, depends on how you use your vault!\n" + "no space after colon is ok:2023-07-08\n" + "standing alone and quoted is fine: \"2021-02-28\"\n" + "IGNORES:\n" + "my template version number has dots for separators (skip): 2025.12.02\n" + "No leading whitespace is questionable?2023-06-08\n" + "existing links (no leading : or space):\n" + " - [[2025-01-01]]\n" + "- [2025-01-01](https:123.com)\n" + " - \"[[2023-11-30]]\"\n" + " - [[\"2024-06-05\"]]\n" + "Not YYYY-MM-DD dates:- 2022-1-1 Euro date: 2022-31-12 or slashes: 2021/09/15\n" + "Bad date for month: 2022-02-30 2022-04-31 2022-06-31 2022-11-31 2022-03-32\n" + "Don't match serial numbers: 2015-12-3135-89\n"; final String subst = "$1\"[[$3-$4]]\"$18"; final Pattern pattern = Pattern.compile(regex, Pattern.MULTILINE | Pattern.COMMENTS); final Matcher matcher = pattern.matcher(string); // The substituted value will be contained in the result variable final String result = matcher.replaceAll(subst); System.out.println("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 Java, please visit: https://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html