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]
  • Character class intersection
    [\w&&[^\d]]
  • 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

Code Generator

Language

Generated Code

import re regex = re.compile(r"^[ \t]*([0]|([-+]?(\d*\.)?\d+)(cm|mm|in|px|pt|pc|Q|em|ex|ch|rem|vw|vh|vmin|vmax|%)){1}([\t ]+([0]|([-+]?(\d*\.)?\d+)(cm|mm|in|px|pt|pc|Q|em|ex|ch|rem|vw|vh|vmin|vmax|%))){0,3}[\t ]*$", flags=re.MULTILINE) test_str = ("0\n" " 0 \n" "0px\n" " 0px 0px 0px 0\n" "0 0\n" " 0cm 0px 0ch 0% \n" " 0 0 \n" "0 0 0\n" " 0 0 0 \n" "0 0 0 0\n" "2px 0\n" "+2px\n" "-3px\n" "0 2px\n" " 3cm \n" "0px\n" "0px 0px 0px\n" " 1px \n" " 2px 2px \n" " 3px 3px 3px \n" " 4px 4px 4px 4px \n" "+4px -4px -4px +4px \n" "-1px \n" " -2px -2px \n" " -3px -3px -3px \n" " -4px -4px -4px -4px \n" "1% \n" " 2% 2vh \n" " 3vw 3vh 3% \n" " 4cm 4pt -4vmin 4vmax \n\n" "# Errors - must not match\n" " \n" "00\n" "0 0px 00 \n" "1px-2px \n" " 2px2px \n" " 3pxf 3px 3px sdsd\n" " 4px-4px 4px 4px \n" "4px4px4px4px \n" "4px 4px 4px 4-px \n" "-4px-4px-4px-4px \n" "--3px\n" "+-3px\n" "-4px-4px -4px- 4px \n" "-4\n" "+5\n" "+0px -0\n" "+0") matches = regex.finditer(test_str) for match_num, match in enumerate(matches, start=1): print(f"Match {match_num} was found at {match.start()}-{match.end()}: {match.group()}") for group_num, group in enumerate(match.groups(), start=1): print(f"Group {group_num} found at {match.start(group_num)}-{match.end(group_num)}: {group}")

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