Setup Factory 9 - Check File for String - scripting

Question

Im am 100% new to Lua and need a way to check my etc/hosts file for a string. The other posts I found were dealing with searching in strings and and reading files line by line.
Here is some of my script which is a combination of some of the examples I found on here:
file = io.open("C:\Windows\System32\drivers\etc\hosts", "a")
function check(file)
if file.match(str, "nbs") then
file:close()
Screen.Next();
else
file:write("\n", %UserIP%, " nbs document")
file:close()
Screen.Next();
end
end;
As you can see Im searching the file hosts for the sting nbs. If it exists I want to move on. If it does not, I plan to append the file with a new line.
The above seems to do nothing when I enter it into my Lua Shell.
EDIT 1: adding full script; this is the full original script + my additions
-- These actions are performed when the Next button is clicked.
-- from _SUF70_Global_Functions.lua:
-- is the "Name:" field empty?
if(g_EditFieldIsEmpty(CTRL_EDIT_01)) then
-- the name field is empty...tell the user that it's a required field
-- and remain on this screen (don't advance to the next one)
-- "Invalid Entry"
local strTitle = SetupData.GetLocalizedString("MSG_INVALID_ENTRY");
-- get the label for the "Name:" edit field (since it may have been translated)
local strFieldName = DlgStaticText.GetProperties(CTRL_STATICTEXT_LABEL_01).Text;
-- strip off the trailing ":" (if present)
strFieldName = String.TrimRight(strFieldName, ":");
-- "The <fieldname> field cannot be empty."
local strPrompt = SetupData.GetLocalizedString("MSG_THE")
..strFieldName
..SetupData.GetLocalizedString("MSG_FIELD_CANNOT_BE_EMPTY");
Dialog.Message(strTitle, strPrompt, MB_OK, MB_ICONEXCLAMATION, MB_DEFBUTTON1);
else
--andrew you added the lines below
file = io.open("C:\Windows\System32\drivers\etc\hosts", "a")
function check(file)
if file.match(str, "test") then
file:close()
Screen.Next()
else
file:write("\n", "test")
file:close()
Screen.Next();
end
end;
-- the "Name:" field isn't empty...so
-- advance to the next screen
-- Screen.Next();
end;

Answer 1

This ended up being the solution I was looking for:
ip = SessionVar.Expand("%UserIP%")
result = TextFile.ReadToString(SessionVar.Expand("%SystemFolder%\\drivers\\etc\\hosts"));
if string.match(result, "nbs") then
Screen.Next()
else
file = io.open("C:\\Windows\\System32\\drivers\\etc\\hosts", "a")
file:write("\n", ip, " nbs document")
file:close()
Screen.Next()
end
In this case I was using the applications built in functions. These seem to make use of C as well so they would not work in a Lua shell.

Answer 2

Your code creates a file handle and defines a function check().
If it is supposed to do more you have to have to add more content. Like a function call to check.
Once you call check you'll most likely face a script error because you call a function file.match which does not exist in native Lua.
file = io.open("C:\Windows\System32\drivers\etc\hosts", "a")
-- this loop will give you each line of the file as a string and you can use string.match
for line in file:lines() do
if line:match("nbs") then
print("I found one!!")
end
end
I'm sure you can take it from here. Please refer to https://www.lua.org/manual/5.3/manual.html#6.8