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

/
/
gm

Test String

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"^chr(1?[0-9]|2[0-2]|X|Y)" test_str = ("chr1 3009844 3009908 DXX 42 -\n" "chr2 3000386 3000450 DXX 15 -\n" "chr3 3000386 3000450 DXX 15 -\n" "chr4 3000386 3000450 DXX 15 -\n" "chr5 3000386 3000450 DXX 15 -\n" "chr6 3000386 3000450 DXX 15 -\n" "chr7 3000386 3000450 DXX 15 -\n" "chr8 3000386 3000450 DXX 15 -\n" "chr9 3000386 3000450 DXX 15 -\n" "chr10 3000386 3000450 DXX 15 -\n" "chr11 3000386 3000450 DXX 15 -\n" "chr12 3000386 3000450 DXX 15 -\n" "chr13 3000386 3000450 DXX 15 -\n" "chr14 3000386 3000450 DXX 15 -\n" "chr15 3000386 3000450 DXX 15 -\n" "chr16 3000386 3000450 DXX 15 -\n" "chr17 3000386 3000450 DXX 15 -\n" "chr18 3000386 3000450 DXX 15 -\n" "chr19 3000386 3000450 DXX 15 -\n" "chrX 3000386 3000450 DXX 15 -\n" "chrY 3000386 3000450 DXX 15 -\n" "chr1_GL456210_random 3000386 3000450 DXX 15 -\n" "chr1_GL456211_random 3000386 3000450 DXX 15 -\n" "chr1_GL456212_random 3000386 3000450 DXX 15 -\n" "chr1_GL456221_random 3000386 3000450 DXX 15 -\n" "chr4_GL456216_random 3000386 3000450 DXX 15 -\n" "chr4_JH584292_random 3000386 3000450 DXX 15 -\n" "chr4_JH584295_random 3000386 3000450 DXX 15 -\n" "chr5_GL456354_random 3000386 3000450 DXX 15 -\n" "chr5_JH584296_random 3000386 3000450 DXX 15 -\n" "chr5_JH584297_random 3000386 3000450 DXX 15 -\n" "chr5_JH584299_random 3000386 3000450 DXX 15 -\n" "chrX_GL456233_random 3000386 3000450 DXX 15 -") matches = re.finditer(regex, test_str, re.MULTILINE) for matchNum, match in enumerate(matches, start=1): print ("Match {matchNum} was found at {start}-{end}: {match}".format(matchNum = matchNum, start = match.start(), end = match.end(), match = match.group())) for groupNum in range(0, len(match.groups())): groupNum = groupNum + 1 print ("Group {groupNum} found at {start}-{end}: {group}".format(groupNum = groupNum, start = match.start(groupNum), end = match.end(groupNum), group = match.group(groupNum))) # 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