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

# coding=utf8 # the above tag defines encoding for this document and is for Python 2.x compatibility import re regex = r""" ([ :]) # look for : and space as possible leading characters ([\"]?) # if there's a quote, disregard it ([0-9]{4}) # find the year - # find the 1st dash ( # Group (4) ( ((0[13578] | (10|12)) # look for 31 day months - # followed by the 2nd dash (0[1-9]|[1-2][0-9]|3[0-1]) # and accept days up to 31 ) | # OR... (02 # look for Feb - # followed by the 2nd dash (0[1-9]|[1-2][0-9])) # and accept up to 29 days | # OR... ((0[469]|11)) # look for 30 day months - # followed by the 2nd dash ((0[1-9]|[1-2][0-9]|30)) # and accept up to 30 days ) ) # closes (4) ([\"]?)([ \"]?)(\s) """ test_str = ("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") subst = "$1\"[[$3-$4]]\"$18" # You can manually specify the number of replacements by changing the 4th argument result = re.sub(regex, subst, test_str, 0, re.MULTILINE | re.VERBOSE) if result: print (result) # Note: for Python 2.7 compatibility, use ur"" to prefix the regex and u"" to prefix the test string and substitution.

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 Python, please visit: https://docs.python.org/3/library/re.html