Lua File Buffering, Writing, and OS Facilities: Time, Date, and Execution

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. file:setvbuf({mode} [, {size}]) *file:setvbuf()* Sets the buffering mode for an output file. There are three available modes: `"no"` no buffering; the result of any output operation appears immediately. `"full"` full buffering; output operation is performed only when the buffer is full (or when you explicitly `flush` the file (see |io.flush()|). `"line"` line buffering; output is buffered until a newline is output or there is any input from some special files (such as a terminal device). For the last two cases, {size} specifies the size of the buffer, in bytes. The default is an appropriate size. file:write({...}) *file:write()* Writes the value of each of its arguments to `file`. The arguments must be strings or numbers. To write other values, use `tostring` |tostring()| or `string.format` |string.format()| before `write`. ============================================================================== 5.8 Operating System Facilities *lua-lib-os* This library is implemented through table `os`. os.clock() *os.clock()* Returns an approximation of the amount in seconds of CPU time used by the program. os.date([{format} [, {time}]]) *os.date()* Returns a string or a table containing date and time, formatted according to the given string {format}. If the {time} argument is present, this is the time to be formatted (see the `os.time` function |os.time()| for a description of this value). Otherwise, `date` formats the current time. If {format} starts with `!`, then the date is formatted in Coordinated Universal Time. After this optional character, if {format} is the string `"*t"`, then `date` returns a table with the following fields: `year` (four digits), `month` (1-12), `day` (1-31), `hour` (0-23), `min` (0-59), `sec` (0-61), `wday` (weekday, Sunday is 1), `yday` (day of the year), and `isdst` (daylight saving flag, a boolean). If {format} is not `"*t"`, then `date` returns the date as a string, formatted according to the same rules as the C function `strftime`. When called without arguments, `date` returns a reasonable date and time representation that depends on the host system and on the current locale (that is, `os.date()` is equivalent to `os.date("%c")`). os.difftime({t2}, {t1}) *os.difftime()* Returns the number of seconds from time {t1} to time {t2}. In POSIX, Windows, and some other systems, this value is exactly `t2 - t1` . os.execute([{command}]) *os.execute()* This function is equivalent to the C function `system`. It passes {command} to be executed by an operating system shell. It returns a status code, which is system-dependent. If {command} is absent, then it returns nonzero if a shell is available and zero otherwise. os.exit([{code}]) *os.exit()* Calls the C function `exit`, with an optional {code}, to terminate

This section covers several functions related to file handling and operating system interactions in Lua. It describes `file:setvbuf` for setting the buffering mode of an output file, `file:write` for writing strings and numbers to a file. It introduces the `os` library, including `os.clock` for CPU time, `os.date` for formatting date and time, `os.difftime` for calculating the time difference between two times, `os.execute` for executing system commands, and `os.exit` for terminating the program.