Why doesn't io:write() write to the output file? - file-io

Question

I'm writing a short script in Lua to replicate Search/Replace functionality. The goal is to enter a search term and a replacement term, and it will comb through all the files of a given extension (not input-determined yet) and replace the Search term with the Replacement term.
Everything seems to do what it's supposed to, except the files are not actually written to. My Lua interpreter (compiled by myself in Pelles-C) does not throw any errors or exit abnormally; the script completes as if it worked.
At first I didn't have i:flush(), but I added it after reading that it is supposed to save any written data to the file (see LUA docs). It didn't change anything, and files are still not written to.
I think it might have something to do with how I'm opening the file to edit it, since the "w" option works (but overwrites everything in my test files).
Source:
io.write("Enter your search term:")
term = io.read()
io.write("Enter your replace term:")
replacement = io.read()
io.stdin:read()
t = {}
for z in io.popen('dir /b /a-d'):lines() do
if string.match(string.lower(z), "%.txt$") then
print(z)
table.insert(t, z)
end
end
print("Second loop")
for _, w in pairs(t) do
print(w)
i = io.open(w, "r+")
print(i)
--i:seek("set", 6)
--i:write("cheese")
--i:flush()
for y in i:lines() do
print(y)
p, count = string.gsub(y, term, replacement, 1)
print(p)
i:write(p)
i:flush()
io.stdin:read()
end
i:close()
end
This is the output I get (which is what I want to happen), but in reality isn't being written to the file:
There was one time where it wrote output to a file, but it only output to one file and after that write my script crashed with the message: No error. The line number was at the for y in i:lines() do line, but I don't know why it broke there. I've noticed file:lines() will break if the file itself has nothing in it and give an odd/gibberish error, but there are things in my text files.
Edit1
I tried do this in my for loop:
for y in i:lines() do
print(y)
p, count = string.gsub(y, term, replacement, 1)
print(p)
i:write(p)
i:seek("set", 3) --New
i:write("TESTESTTEST") --New
i:flush()
io.stdin:read()
end
in order to see if I could force it to write regular text. It does but then it crashes with No error and still doesn't write the replacement string (just TESTESTTEST). I don't know what the problem could be.

Answer 1

I guess, one can't write to file while traversing its lines
for y in i:lines() do
i:write(p)
i:flush()
end