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
  • Match everything enclosed
    (?:...)
  • Capture everything enclosed
    (...)
  • 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

r"
"
gm

Test String

Code Generator

Generated Code

# coding=utf8 # the above tag defines encoding for this document and is for Python 2.x compatibility import re regex = r"(?:[!]\[(?P<caption>.*?)\])\((?P<image>.*?)\)" test_str = ("This is a regex to detect markdown image links of the form ![image caption](image URL)\n\n" "Here are some markdown links\n" "- [pandoc-fignos](https://github.com/tomduck/pandoc-fignos): Numbers figures and figure references.\n" "The images section will walk you through how to add and reference images so that the pandoc system can properly number them. For example, this [figure](./ch0_1_images.md#fig:ch0_1_images-1) illustrates a VOD curve for a packaged watergel explosive and this [figure](./ch0_1_images.md#fig:ch0_1_images-2) depicts a circular arc.\n" "## [Equations](./ch0_2_equations.md#sec:ch0_2_equations-1)\n" "The equations section will discuss how to use equations and reference them properly. See the [internal energy equation](./ch0_2_equations.md#eq:ch0_2_equations-1) or the [detonation pressure](./ch0_2_equations.md#eq:ch0_2_equations-2)\n" "This string does not contain any links\n\n" "Here are some image links:\n" "![Caption.](image.png){#fig:id}\n" "![Caption.](image.png){#fig:id tag=\"B.1\"}\n" "![This is a sample image representing the VOD curve of a packaged Watergel explosive.](../assets/1v6C9yek3pHsXSeOlR4glzDMkFqFHizR6VXr79tEOnY=.png){#fig:ch0_1_images-1 width=100%}\n" "![](../../assets/E5WnRoSH_Dqrzl8f5_ZJ9AjWc-53BgiBqD_xTqEp6pM=.png)\n" "![](../../assets/l2mxAo3IR1dc3Wrgt7Ulqhcm_8nwqFw5UY7pUI3X0oI=.png)\n" "![](../../assets/Y7jjv0ceQH5Ew5O32U2Z_N7ARBfKn2FnHnUoUt_DYbA=.png)\n" "![](../../assets/eOvy-JcdA7pjoDJS4rIgG5RgDfYJ4PY11Owbgy5DHWM=.png)\n" "![](../../assets/XwMrG0o__iLF5nStoSPUuJ81ffxafRBWAVnEcGo10Yo=.png)\n" "![](../../assets/AfHKsc518nK6Ew2MHJt96lJMkTiVAyIiuva6L-lRQaQ=.png)\n" "![](../../assets/JyDHFl6DyL1mw5EI-pSb9ssNzmbsEaSPQn5AOiZqeiM=.png)\n" "![](../../assets/BYGvFWn41qFZuU3C7Jyd1uHjs8Cib8eEJod0sIze9S0=.png)\n" "![](../../assets/77U97Em8AN06LCGVxH6UQ_Lh3OZkNsJRkMZY1nBMVrA=.png)\n" "![](../../assets/iPkPth_Vh_wSgeD0wqxlctDyDEmgHfYuhTqBQE6mynI=.png)\n" "![](../../assets/h57_b4_XeFd5SR1iYLu9WsYNy_n8sM6rPbQdGephk1c=.png)\n" "![](../../assets/u8Y_44VG3-pD8fweuazkSN9fflhJfgCqOtc2ooP2sVM=.png)\n" "![](../../assets/dc-ExOEXIWnH0qwVHTSNmFljUwyKS0xeEYFxS98ZEYg=.png)\n" "![](../../assets/nJZLBZEOCiOT2P1F2c5mVQZrCrIJB5i1EnRgT767WWo=.png)\n" "![](../../assets/ilG_dm7Lr3315RFsUdJCW7tkJbTZlnmV_NNKFBDeyxc=.png)\n" "![](../../assets/1v6C9yek3pHsXSeOlR4glzDMkFqFHizR6VXr79tEOnY=.png)\n" "![](../../assets/Bw1eWhlyutzMa8Eg94-VnSk_TsffrBLeoZKWySkMwIw=.png)\n" "![](../../assets/9RIkA4mInkKNSIxMi7ctUozBJPUqlHPugIfG2yr37Co=.png)\n" "![Hyperbola](../../assets/300px-Hyperbola_properties.svg.png)\n" "![Hyperbola](../../assets/HyperbolaAnatomyLeft.png)\n" "![Hyperbola](../../assets/HyperbolaAnatomyRight.png)\n" "![](../../assets/IsXLnPl1wKraeLnryg2rOxtYdGSSHg8vTTN1ObV0Dt8=.png)") 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