using System;
using System.Text.RegularExpressions;
public class Example
{
public static void Main()
{
string pattern = @"(?xsm) # free-spacing mode, multi-line
(?=.*?pig) # lookahead: if pig is not there, fail right away to save the effort
(?: # start counter-line-skipper (lines that don't include pig)
(?: # 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
)
# for each line skipped, let Group 1 match an ever increasing portion of the numbers string at the bottom
(?= # lookahead
[^:]+ # skip all chars that are not colons
( # start Group 1
(?(1)\1) # if Group 1 is set, match Group 1
# (?>\1?) # alternate phrasing for the above
:\d+ # match a colon and some digits
) # end Group 1
) # end lookahead
)*+ # end counter-line-skipper: zero or more times
.*? # match
\K # drop everything we've matched so far
pig # match pig (this is the match!)
(?=[^:]+(?(1)\1):(\d+)) # capture the next number to Group 2";
string substitution = @"\2";
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