using System;
using System.Text.RegularExpressions;
public class Example
{
public static void Main()
{
string pattern = @"\$\$(?:[^$][^$])*\$\$";
string input = @"Lorem ipsum dolor sit ame $ a = \{ b, c \} $ Lorem 100 \$ ipsum
$$ \left \{
\begin{array}{cl}y_1 =&3 x_1 - x_2 + x_3\\y_2 =&2 x_2\\y_3 =&x_1 - x_2 + 3 x_3\end{array}
\right.
\Leftrightarrow \left \{
\begin{array}{cl}8 x_1 =&3 y_1 + y_2 -y_3\\8 x_2 =&4 y_2\\8 x_3 =&-y_1 + y_2 + 3 y_3\end{array}
\right.
$$ Lorem ipsum dolor
$$ \left \{
\begin{array}{cl}y_1 =&3 x_1 - x_2 + x_3\\y_2 =&2 x_2\\y_3 =&x_1 - x_2 + 3 x_3\end{array}
\right.
\Leftrightarrow \left \{
\begin{array}{cl}8 x_1 =&3 y_1 + y_2 -y_3\\8 x_2 =&4 y_2\\8 x_3 =&-y_1 + y_2 + 3 y_3\end{array}
\right.
$$ Lorem ipsum dolor ";
RegexOptions options = RegexOptions.Multiline | RegexOptions.Singleline;
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