Question

Sets and gets the file position,
measured from the beginning of the file,
to the position given by offset plus a base
specified by the string whence, as follows:

• "set": base is position 0 (beginning of the file);
• "cur": base is current position;
• "end": base is end of file;

In case of success, function seek returns the final file position,
measured in bytes from the beginning of the file.
If this function fails, it returns nil,
plus a string describing the error.

The default value for whence is "cur",
and for offset is 0.
Therefore, the call file:seek() returns the current
file position, without changing it;
the call file:seek("set") sets the position to the
beginning of the file (and returns 0);
and the call file:seek("end") sets the position to the
end of the file, and returns its size.