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Lua 5.3 Reference Manual

Copyright © 2015 Lua.org, PUC-Rio. Freely available under the terms of the Lua license.

Operating System Facilities

This library is implemented through table os

os.clock ()

Returns an approximation of the amount in seconds of CPU time used by the program.

os.date ([format [, time]])

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 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, 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). This last field may be absent if the information is not available.

If format is not "*t", then date returns the date as a string, formatted according to the same rules as the ISO 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. (More specifically, os.date() is equivalent to os.date("%c").)

On non-POSIX systems, this function may be not thread safe because of its reliance on C function gmtime and C function localtime.

os.difftime (t2, t1)

Returns the difference, in seconds, from time t1 to time t2 (where the times are values returned by os.time). In POSIX, Windows, and some other systems, this value is exactly t2-t1.

os.getenv (varname)

Returns the value of the process environment variable varname, or nil if the variable is not defined.

os.setlocale (locale [, category])

Sets the current locale of the program. locale is a system-dependent string specifying a locale; category is an optional string describing which category to change: "all", "collate", "ctype", "monetary", "numeric", or "time"; the default category is "all". The function returns the name of the new locale, or nil if the request cannot be honored.

If locale is the empty string, the current locale is set to an implementation-defined native locale. If locale is the string "C", the current locale is set to the standard C locale.

When called with nil as the first argument, this function only returns the name of the current locale for the given category.

This function may be not thread safe because of its reliance on C function setlocale.

os.time ([table])

Returns the current time when called without arguments, or a time representing the local date and time specified by the given table. This table must have fields year, month, and day, and may have fields hour (default is 12), min (default is 0), sec (default is 0), and isdst (default is nil). Other fields are ignored. For a description of these fields, see the os.date function.

The values in these fields do not need to be inside their valid ranges. For instance, if sec is -10, it means -10 seconds from the time specified by the other fields; if hour is 1000, it means +1000 hours from the time specified by the other fields.

The returned value is a number, whose meaning depends on your system. In POSIX, Windows, and some other systems, this number counts the number of seconds since some given start time (the "epoch"). In other systems, the meaning is not specified, and the number returned by time can be used only as an argument to os.date and os.difftime.

Last update: Fri Nov 27 18:43:18 BRST 2015