Regular Expressions 101

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Function

  • Match
  • Substitution
  • List
  • Unit Tests (14)
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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

Code Generator

Language

Generated Code

import re regex = re.compile(r""" <link(?=[^<>]*?opensearch)(?:[^h]+|h(?!ref))*+href=["']?\K([^<>'"\s]+(?:\/(?!>)|\b))(?=[^<>]*>) """, flags=re.IGNORECASE | re.MULTILINE | re.VERBOSE) test_str = ("This should succeed:\n" "<link rel=\"search\" type=\"application/opensearchdescription+xml\" href=\"http://example.com/tsr-opensearch/\" title=\"\" />\n" "<link rel=\"search\" type=\"application/opensearchdescription+xml\" href=\"http://www.example.com/search.xml\" title=\"\" />\n" "<link rel=\"search\" type=\"application/opensearchdescription+xml\" href=\"/search.xml\" title=\"\" />\n" "<link rel=\"search\" type=\"application/opensearchdescription+xml\" href=\"search.xml\" title=\"\" />\n" "<link rel=\"search\" type=\"application/opensearchdescription+xml\" href=\".search.xml\" title=\"\" />\n" "<link rel=\"search\" type=\"application/opensearchdescription+xml\" href=\"./search.xml\" title=\"\" />\n" "<link rel=\"search\" type=\"application/opensearchdescription+xml\" href=\".search.xml\" title=\"\" />\n" "<link rel=\"search\" type=\"application/opensearchdescription+xml\" href='http://www.example.com/search.xml' title=\"\" />\n" "<link rel=\"search\" type=\"application/opensearchdescription+xml\" href=http://www.example.com/search.xml title=\"\" />\n" "<link rel=\"search\" type=\"application/opensearchdescription+xml\" href=http://www.example.com/search.xml>\n" "<link rel=\"search\" type=\"application/opensearchdescription+xml\" href=http://www.example.com/search.xml />\n" "<link rel=\"search\" type=\"application/opensearchdescription+xml\" href=http://www.example.com/search.xml />\n" "<link rel=\"search\" type=\"application/opensearchdescription+xml\" href=http://www.example.com/search.xml/>\n" "<link rel=\"search\" type=\"application/opensearchdescription+xml\" href=http://www.example.com/dsfdsf/search.xml />\n" "<link rel=\"search\" type=\"application/opensearchdescription+xml\" href=http://www.example.com/search.xml/ />\n" "<link rel=\"search\" type=\"application/opensearchdescription+xml\" href=http://www.example.com/search.xml/ />\n" "<link rel=\"search\" type=\"application/opensearchdescription+xml\" href=http://href.example.com/search.xml/ />\n" "<link rel=\"search\" type=\"application/opensearchdescription+xml\" hre href=http://href.example.com/search.xml/ />\n" "<link rel=\"search\" type=\"application/opensearchdescription+xml\" ref=\"adfsf\" href=http://href.example.com/search.xml/ />\n\n" "Should fail:\n" "<link rel=\"stylesheet\" type=\"text/css\" href=\"theme.css\">\n" "<link rel=\"search\" type=\"application/opensearchdescription+xml\" href= http://www.example.com/search.xml />\n" "<link rel=\"search\" type=\"application/opensearchdescription+xml\" href= http://www.example.com/search.xml>\n" "link rel=\"search\" type=\"application/opensearchdescription+xml\" href=http://www.example.com/search.xml>\n" "link rel=\"search\" type=\"application/opensearchdescription+xml\" href=http://www.example.com/search.xml />\n" "<link rel=\"search\" type=\"application/opensearchdescription+xml\" href=http://www.example.com/search.xml") 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