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

r"
"
gm

Test String

Code Generator

Generated Code

using System; using System.Text.RegularExpressions; public class Example { public static void Main() { string pattern = @"(?<=\W)\$[a-zA-Z_\\\{\}= +']+\$"; string input = @"We try to quantitatively capture these characteristics by defining a set of indexes, which can be computed using the mosaic image and the corresponding ground truth: \begin{itemize} \item $\mu_{A_T}$ and $\sigma_{A_T}$, the mean and standard deviation of the tiles area $A_T$, respectively; \item $\rho_\text{filler}$, the ratio between the filler area and the overall mosaic are, computed as $\rho_\text{filler}=\frac{\sum_{T \in \mathcal{T} A_T}}{A}$, being $A$ the area of the mosaic; \item \todo{does it worth?}; \item \todo{does it worth?}; \item $\mu_{C_T}$, the mean of the tiles \emph{color dispersion} $C_T$, being $C_T = \sigma_R+\sigma_G+\sigma_B$, where $\sigma_R$, $\sigma_G$ and $\sigma_B$ are the standard deviation of the red, green and blue channel values of the pixels within the tile $T$. After applying a method to an image, we compare the segmented image (i.e., the result) against the ground truth and assess the performance according to the following three metrics: \begin{itemize} \item average tile precision $P$ \item average tile recall $R$ \item tile count error $C$ \end{itemize} Let $T$ be a tile on the ground truth $\mathcal{T}$ with area $A_T$. Let $T'$ be the tile in the segmented image which mostly overlaps $T$ and let $A_{T'}$ be the area of $T$; let $A_{T \cap T'}$ be the overlapping area between $T$ and $T'$. Let $n$ and $n'$ the number of tiles respectively in the ground truth and in the segmented image. Metrics are defined as: \begin{align} P &amp;= \frac{1}{n} \sum_{T \in \mathcal{T}} \frac{A_{T \cap T'}}{A_{T'}} \\ R &amp;= \frac{1}{n} \sum_{T \in \mathcal{T}} \frac{A_{T \cap T'}}{A_T} \\ C &amp;= \frac{|n-n'|}{n} \end{align} We try to quantitatively capture these characteristics by defining a set of indexes, which can be computed using the mosaic image and the corresponding ground truth: \begin{itemize} \item $\mu_{A_T}$ and $\sigma_{A_T}$, the mean and standard deviation of the tiles area $A_T$, respectively; \item $\rho_\text{filler}$, the ratio between the filler area and the overall mosaic are, computed as $\rho_\text{filler}=\frac{\sum_{T \in \mathcal{T} A_T}}{A}$, being $A$ the area of the mosaic; \item \todo{does it worth?}; \item \todo{does it worth?}; \item $\mu_{C_T}$, the mean of the tiles \emph{color dispersion} $C_T$, being $C_T = \sigma_R+\sigma_G+\sigma_B$, where $\sigma_R$, $\sigma_G$ and $\sigma_B$ are the standard deviation of the red, green and blue channel values of the pixels within the tile $T$. After applying a method to an image, we compare the segmented image (i.e., the result) against the ground truth and assess the performance according to the following three metrics: \begin{itemize} \item average tile precision $P$ \item average tile recall $R$ \item tile count error $C$ \end{itemize} Let $T$ be a tile on the ground truth $\mathcal{T}$ with area $A_T$. Let $T'$ be the tile in the segmented image which mostly overlaps $T$ and let $A_{T'}$ be the area of $T$; let $A_{T \cap T'}$ be the overlapping area between $T$ and $T'$. Let $n$ and $n'$ the number of tiles respectively in the ground truth and in the segmented image. Metrics are defined as: \begin{align} P &amp;= \frac{1}{n} \sum_{T \in \mathcal{T}} \frac{A_{T \cap T'}}{A_{T'}} \\ R &amp;= \frac{1}{n} \sum_{T \in \mathcal{T}} \frac{A_{T \cap T'}}{A_T} \\ C &amp;= \frac{|n-n'|}{n} \end{align}"; RegexOptions options = RegexOptions.Multiline; foreach (Match m in Regex.Matches(input, pattern, options)) { Console.WriteLine("'{0}' found at index {1}.", m.Value, m.Index); } } }

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 C#, please visit: https://msdn.microsoft.com/en-us/library/system.text.regularexpressions.regex(v=vs.110).aspx