using System;
using System.Text.RegularExpressions;
public class Example
{
public static void Main()
{
string pattern = @"(?xsm) # free-spacing mode, multi-line
(?=.*?pig) # fail right away if pig isn't there
(?=
( # Group 1
(?: # skip one line that doesn't have pig
^ # beginning of line
(?:(?!pig)[^\r\n])* # zero or more chars not followed by pig
(?:\r?\n) # newline chars
)
(?:(?1)|[^:]+) # recurse Group 1 OR match all chars that are not a :
(:\d+) # match a sequence of digits
)? # End Group 1
) # End lookahead. Group 1, if set, now contains the number of lines skipped
.*?\Kpig # match pig
(?=.*?(?(2)\2):(\d+))";
string substitution = @"\3";
string input = @"my cat pi g
dog pi g
my pig
my cow
my mouse
:1:2:3:4:5:6:7";
Regex regex = new Regex(pattern);
string result = regex.Replace(input, substitution, 1);
}
}
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