regex to match repetitive text divided by hash character that can repeat multiple times in multi line string

Question

i have the following regex i'm using with C#

^.*(#\w+?#.+?#.+?#.+?#.+?:).*$

I need to be able to extract the last occurrence of a specifically formatted string within a multi line string

The format can be :

#test12345-abc#slkjs3234-df#slkj23423#slkjdj2343:{asdf9230-232_jk233}

or

#test12345-abc#slkjs3234-df#slkj23423#slkjdj2343:

and could have the format appear 1 or more times and back to back see examples below:

Example 1:

jlkjlkjlkjlkj
lkjlkjlj lkjlkj  #test12345-abc#slkjs3234-df#slkj23423#slkjdj2343:{asdf9230-232_jk233}  lkjlj
slkjlj

Example 2:

jlkjlkjlkjlkj
lkjlkjlj lkjlkj #test12345-abc#slkjs3234-df#slkj23423#l23lkj22:{asdf9230-232_jk233} #test12345-abc#slkjs3234-df#slkj23423#Other:{asdf9230-232_jk233}  lkjlj
slkjlj

Example 3:

jlkjlkjlkjlkj
lkjlkjlj lkjlkj  #test12345-abc#slkjs3234-df#slkj23423#slkjdj2343:  lkjlj
slkjlj

Example 4:

jlkjlkjlkjlkj
lkjlkjlj lkjlkj #test12345-abc#slkjs3234-df#slkj23423#l23lkj22: #test12345-abc#slkjs3234-df#slkj23423#Other:  lkjlj
slkjlj

i'm struggling to find the proper regex that would look for both the examples and in the different positions in the examples ?? thanks

Answer 1

You can use

var result = Regex.Match(text, @"(?:#\w+(?:-\w+)?)+(?::{[\w-]+})?", RegexOptions.RightToLeft)?.Value;

See the regex demo . Note that the RegexOptions.RightToLeft option makes the regex engine search for a match from the end of the string, so you get the last match if there are more than one.

Details

• (?:#\\w+(?:-\\w+)?)+ - one or more repetitions of
  • # - a # char
  • \\w+ - one or more word chars (letters, digits, underscores)
  • (?:-\\w+)? - an optional non-capturing group matching 1 or 0 occurrences of - and then 1+ word chars
• (?::{[\\w-]+})? - an optional non-capturing group:
  • : - a colon
  • {[\\w-]+} - a { char, then one or more letters, digits, underscores or hyphens and then a } char.