How to check if string contains certain word?

Before I begin, I would like to point out that you're not using GMatch correctly, based upon from the research I conducted, as I found that it's used for Loops, and not itself alone (According to the Wiki, at least). I would also like to disclaim that I will not be rewriting your code, otherwise I'm doing the work for you. :P

Now, to begin. >:)

To accomplish what you're trying to do, there're 2 ways you could go about this; you could use:

1. GMatch (when used correctly) - Uses String Patterns (as far as I know); however, you would not use this to accomplish what you're trying to do

2. Find - This will only return the position of where the keyword is at, and not the word itself; it will also only search for the matching keyword, then stop the iteration

3. Match - Similar to Find, but the difference is that it'll return the word (not the entire word, however)

Before we proceed, I would like to add a string & a table to handle all this, w/o the need of re-typing over-and-over again:

local String = 'Hello World! I\'m on Scripting Helpers!' -- This string will be used in the code to example & show what the listed functions (& loop/ function thingy..?) do; variable "String" represents the string it is set to

String = string.lower(String) -- Lower-cases the entire string; string.lower is used to lowercase a specified string; I am aware of String:lower(), but I wanted to take a step back for once :P

local toFind = { -- Table "toFind" will handle the data (personally, I like to keep my code neat & clean in this fashion :) ); "toFind" contains the tables "Strings" & "StringPatterns," which contain the data to use later on (although, both serve difference functions)
	-- Tables are used to hold data & information, such as objects, strings, numbers, etc.
	Strings = { -- Table "Strings" will be used for functions "Find" & "Match,"; table "Strings" contains 2 of the keywords that the later functions will use
		'world', -- String 'world' is a, well, string value, and will be used for the later functions
		'hello' -- Same function will be performed as w/ string 'world'
	}, -- Ends data (storage) (for table "Strings")
	StringPatterns = { -- I'm not familiar w/ String Patterns very well, but I'll do my best to explain; String Patterns are used to get the parts of a string & return them, or get a match(es) in strings(?) (I'm not too sure how to explain this; if anyone has any information or a better explanation, please inform me & let me know ;-;)
		'h%a+' -- This will be used for "GMatch"; the "h" in the string is used to return keywords that start w/ a, well, "h", while "%a+" will be used to return the whole word; "%a" in String Patterns is used to match lower & upper case characters (letters), while the "+" is used to retrieve the full word(s)/ string (the Wiki explains this better ;-;)
	}
}

Lets start w/ GMatch: GMatch is a function that will iterate through the string, then return them( I believe? If anyone has a better explanation to this, please let me know; I'm not familiar w/ GMatch, and I'm going off of the Wiki & how its used); think of it as a table, but not a table at the same time:

for v in string.gmatch(String, toFind.StringPatterns[1]) do -- Variable "v" represents the word/ letter/ etc returned from "GMatch," while "GMatch" returns the characters (letters, numbers, etc) found w/in the specific string ("String" in this case)
	print(v, 'GMatch Result') -- Will print the word "v" represents, & will print "GMatch Result" on the same line; print, well, prints data into the Output
end

Now, after the code is fired, it'll return 2 results in the Output; this is what will be returned:

--[[
	hello GMatch Result -- B/c we gave "GMatch" an argument to return words that start w/ an "h" & return the whole word, it prints this & the following (I hope this better explains what I talked about earlier ;-;)
	helpers GMatch Result
--]]

However, this will not help you accomplish what you're trying to do.

Now, onto functions I'm more familiar w/! :D We'll be using function Find in our next example, following function "Match". :)

For the "Find" function, it's used to iterate through a specified string (value), and return the first keyword found; however, it will not return the word itself, but the position of it. This is how the "Find" function would be used:

print(string.find(String, toFind.Strings[1]), 'Find Result') -- I don't think I need to explain "print" again :P
-- "Find" has 2 arguments that you need to give to it: the first argument is the string to iterate through (durr <->), and the second argument is the word to find when iterating & return (its position)

And when we fire that above code, this is what will be returned in the Output:

--[[
	7 Find Result -- Note how it returned "World"s position, which is 7 characters after "Hello" begins, and not the word itself
--]]

But, that's only one of the 3 that can be used! :O

Now, for the "Match" function, it's used to iterate through a specified string (value), and return the first keyword found; unlike the "Find" function, it returns the word (it was given) that was found. This is how the "Match" function would be used:

print(string.match(String, toFind.Strings[2]), 'Match Result') -- Again, I don't think I need to explain "print" again XP
-- "Match" also has 2 argument that you need to give it: the first being the specified string to iterate through, and the second being what keyword to find & return it

Aaaaand when we fire the above code, this is what will return in the Output:

--[[
	he Match Result -- Note how it returned the keyword, unlike how "Find" only returned the position; although, "Match" only returned the keyword, 'he,' which was given to it, and not the entire word; I believe that's where "GMatch" shines when it comes to this
--]]

And wa-la! That's 3 ways to check & find specific a keyword(s) in a string! :D Plays Final Fantasy Victory Theme

I forgot to mention before that w/ "Find" & "Match", if they don't find the keyword that was given to them, they will return nil, so be careful when using them. :o

Stuff touched on, but didn't go into great detail about

1. "Find" Function

2. "Match" Function

3. "GMatch" Function - Tbh, this was a nightmare ;-;

4. String Patterns

5. The Output - Retrieves & shows data (such as strings & numbers), warnings, & errors.

6. Loops

7. Tables -- Hold (or contains) data, such as strings, numbers, objects, etc.

8. Functions

9. Nil

10. Iteration

I hope this helped you in any way. :)