File Input Output

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-- Find the length of a file

--   filename: file name

-- returns

--   len: length of file

--   asserts on error

function length_of_file(filename)

  local fh = assert(io.open(filename, "rb"))

  local len = assert(fh:seek("end"))

  fh:close()

  return len

end



-- Return true if file exists and is readable.

function file_exists(path)

  local file = io.open(path, "rb")

  if file then file:close() end

  return file ~= nil

end



-- Guarded seek.

-- Same as file:seek except throws string

-- on error.

-- Requires Lua 5.1.

function seek(fh, ...)

  assert(fh:seek(...))

end

Old Lua 4 Stuff

The following examples are from Lua 4, included here only for historical reasons.

-- Guarded readfrom (Lua4)

--   [f]: file name

-- Note: In Lua5 use io.input().

function readfrom(f)

  local h, err

  if f then h, err = %readfrom(f)

  else      h, err = %readfrom()

  end

  affirm(h, "can't read from " .. (f or "stdin") .. ": " ..

         (err or ""))

  return h

end



-- Guarded writeto (Lua4)

--   [f]: file name

-- Note: In Lua5 use io.output().

function writeto(f)

  local h, err

  if f then h, err = %writeto(f)

  else      h, err = %writeto()

  end

  affirm(h, "can't write to " .. (f or "stdout") .. ": " ..

         (err or ""))

  return h

end



-- Guarded dofile (Lua4)

--   [f]: file name

-- Note: In Lua5, dofile throws on error.

function dofile(f)

  affirm(%dofile(f), "error while executing " .. f)

end



-- Guarded seek (Lua4)

--   f: file handle

--   w: whence to seek

--   o: offset

function seek(f, w, o)

  local ok, err

  if     o then ok, err = %seek(f, w, o)

  elseif w then ok, err = %seek(f, w)

  else          ok, err = %seek(f)

  end

  affirm(ok, "can't seek on " .. f .. ": " .. (err or ""))

end





-- Find the length of a file (Lua4)

--   f: file name

-- returns

--   len: length of file

function length_of_file(f)

  local h, len

  h = openfile(f, "r")

  len = seek(h, "end")

  closefile(h)

  return len

end

--JayCarlson - original (Lua 4 version)

See Also

• FileSystemOperations