การเขียนและเพิ่มข้อมูลลงไฟล์

local f = io.open("output.txt", "w")
if f then
  f:write("Hello, ")
  f:write("World")
  f:write("!\n")
  f:write("Line 2\n")
  f:close()
end

local f = io.open("log.txt", "w")
f:write("Name: ", "Alice", "\n")
f:write("Age: ", 30, "\n")
f:write("Score: ", string.format("%.1f", 95.5), "\n")
f:close()

local data = {
  {name="Alice", score=95, grade="A"},
  {name="Bob",   score=87, grade="B"},
}

local f = io.open("report.txt", "w")
f:write(string.format("%-12s  %5s  %s\n","Name","Score","Grade"))
f:write(string.rep("-",25) .. "\n")
for _, r in ipairs(data) do
  f:write(string.format("%-12s  %5d  %s\n",r.name,r.score,r.grade))
end
f:close()

local function appendLog(msg)
  local f = io.open("app.log", "a")
  if f then
    local ts = os.date("%Y-%m-%d %H:%M:%S")
    f:write(string.format("[%s] %s\n", ts, msg))
    f:close()
  end
end

appendLog("Server started")
appendLog("User logged in: Alice")
appendLog("Request processed")

local f = io.open("stream.txt", "w")
for i = 1, 5 do
  f:write("Line " .. i .. "\n")
  f:flush()   -- ensure each line is on disk
  -- simulate work
end
f:close()

local f = io.open("bytes.bin", "wb")
if f then
  -- Write raw bytes
  f:write(string.char(0xFF, 0x00, 0xAB, 0xCD))
  -- Write a 4-byte little-endian integer (Lua 5.3+)
  f:write(string.pack("<I4", 12345))
  f:close()
  print("Written binary file")
end

-- io.write to stdout
io.write("Enter name: ")
-- (would read input here)

-- f:write to file
local f = io.open("out.txt", "w")
f:write("No auto newline")
f:write(" appended directly")
f:write("\n")  -- explicit newline
f:close()

-- print adds tabs and newline automatically
print("a", "b", "c")   -- a  b  c (tab-separated)

local function atomicWrite(path, content)
  local tmp = path .. ".tmp"
  local f, err = io.open(tmp, "w")
  if not f then return nil, err end
  f:write(content)
  f:close()
  -- os.rename is atomic on most filesystems
  local ok, err2 = os.rename(tmp, path)
  if not ok then
    os.remove(tmp)
    return nil, err2
  end
  return true
end

local function writeCSV(path, headers, rows)
  local f = io.open(path, "w")
  if not f then return end
  f:write(table.concat(headers, ",") .. "\n")
  for _, row in ipairs(rows) do
    local fields = {}
    for _, h in ipairs(headers) do
      fields[#fields+1] = tostring(row[h] or "")
    end
    f:write(table.concat(fields, ",") .. "\n")
  end
  f:close()
end

writeCSV("data.csv",
  {"name","age","score"},
  {{name="Alice",age=30,score=95},{name="Bob",age=25,score=87}}
)

local f = io.open("out.txt", "w")

-- Chaining writes
local ok, err = f:write("line1\n"):write("line2\n"):write("line3\n")
if not ok then
  print("Write failed:", err)
else
  print("All writes succeeded")
end
f:close()