How to find a duplicate string with Pattern Matching?

Question

I have a string similar to this:

[13:41:25] [100:Devnull]: 01:41:20, 13:41:21> |Hunit:Player-3693-07420299:DevnullYour [Chimaera Shot] hit |Hunit:Creature-0-3693-1116-3-87318-0000881AC4:Dungeoneer's Training DummyDungeoneer's Training Dummy 33265 Nature. 

In case you wonder, it's from World of Warcraft.

I'd like to end with something like this:

[13:41:25] [100:Devnull]: 01:41:20, 13:41:21> Your [Chimaera Shot] hit Dungeoneer's Training Dummy 33265 Nature. 

If you notice, "Dungeoneer's Training Dummy" is printed twice. I've managed to get rid of the first "|Hunit" portion with something like this:

str = "[13:41:25] [100:Devnull]: 01:41:20, 13:41:21> |Hunit:Player-3693-07420299:DevnullYour [Chimaera Shot] hit |Hunit:Creature-0-3693-1116-3-87318-0000881AC4:Dungeoneer's Training DummyDungeoneer's Training Dummy 33265 Nature."
str = string.gsub(str, "|Hunit:.*:.*Your", "Your")

Which returns this:

print(str)    # => [13:41:25] [100:Devnull]: 01:41:20, 13:41:21> Your [Chimaera Shot] hit |Hunit:Creature-0-3693-1116-3-87318-0000881AC4:Dungeoneer's Training DummyDungeoneer's Training Dummy 33265 Nature.

I then add a second gsub:

str = string.gsub(str, "|Hunit:.*:", "")
print(str) # => [13:41:25] [100:Devnull]: 01:41:20, 13:41:21> Your [Chimaera Shot] hit Dungeoneer's Training DummyDungeoneer's Training Dummy 33265 Nature.

But the double "Dungeoneer's Training Dummy" string is repeated, obviously.

How could I get rid of the duplicated string? This string can be anything else, in this case is "Dungeoneer's Training Dummy", but it can be the name of any other target.

Answer 1

You can try something like this:

str = "[13:41:25] [100:Devnull]: 01:41:20, 13:41:21> Your [Chimaera Shot] hit Dungeoneer's Training DummyDungeoneer's Training Dummy 33265 Nature."
-- find a string that starts with 'hit', has some number of non-digits
-- and ends with one or more digit and one or more characters.
-- these characters will be "captured" into three strings,
-- which are then passed to the "replacement" function.
-- the returned result of the function replaces the value in the string.
str = str:gsub("(hit%s+)([^%d]+)(%d+.+)", function(s1, s2, s3)
    local s = s2:gsub("%s+$","") -- drop trailing spaces
    if #s % 2 == 0 -- has an even number of characters
    and s:sub(0, #s / 2) -- first half
    == -- is the same
    s:sub(#s / 2 + 1) -- as the second half
    then -- return the second half
      return s1..s:sub(#s / 2 + 1)..' '..s3
    else
      return s1..s2..s3
    end
  end)
print(str)

This prints: [13:41:25] [100:Devnull]: 01:41:20, 13:41:21> Your [Chimaera Shot] hit Dungeoneer's Training Dummy

This code will attempt to extract the name of the target and check if the name is a full duplicate. If the match fails, it returns the original string.