Step by step (LUA System Library)

To ensure high portability, Lua provides only a small number of features, especially OS-related libraries. However, Lua also provides some extension libraries, such as POSIX libraries. For file operations, this library only providesOS. RenameFunctions andOS. RemoveFunction.

1. Date and Time:
In Lua, the functionTimeAndDateAll date and time functions are provided.
If the time function is called without any parameters, it returns the current date and time in number format. If a table is used as a parameter, it returns a number indicating the date and time described in the table. The valid fields of the table are as follows:

Field name	Description
Year	A complete year
Month	01-12
Day	01-31
Hour	00-23
Min	00-59
Sec	00-59
Isdst	Boolean value. True indicates timeout.

Print (OS. Time {year = 1970, month = 1, Day = 1, hour = 8, min = 0 })-- Beijing is the UTC + 8 zone, so if hour is equal to UTC, it indicates 0 of UTC.
Print (OS. Time ())-- The number of seconds that the current time passes through from 00:00:00. The output value is 1333594721
The date function is the inverse function of time, that is, you can convert the numeric value returned by time to a more advanced readable format. The first parameter is a formatted string, indicating the expected date return format, the second parameter is the number of the date and time. The default value is the current date and time. For example:

 1 Dd = OS. Date ( "  * T  " ,OS. Time ()) --  If the formatted string is "* t", the function returns a date object in table format.  If it is "! * T "indicates the UTC time format.
  2   Print ( "  Year =  " .. Dd. Year)
 3   Print ( "  Month =  " .. Dd. month)
4   Print ( "  Day =  " .. Dd. Day)
 5   Print ( "  Weekday =  " .. Dd. wday) --  The day of a week, and Sunday is the first day.  
  6   Print ("  Yearday =  " .. Dd. yday) --  The day of the year, and the first day of the month  
  7   Print ( "  Hour =  " .. Dd. hour)
 8   Print ( "  Min =  " .. Dd. min)
 9   Print ( "  SEC =  " .. Dd. Sec)
 10      
 11   --[[  
  12   Year = 2012
  13   Month = 4
  14   Day = 5
 15   Weekday = 5
  16   Yearday = 96
  17   Hour = 11
  18   Min = 13
  19   SEC = 44
  20   --  ] 

The format ID of the date function is exactly the same as that of the strftime function in the C Runtime Library. See the following table:

Keywords	Description
%	Abbreviation of the number of days in a week, such as wed
%	The full name of days in one week, such as Friday
% B	Abbreviation of month, such as SEP
% B	The full name of a month, such as September.
% C	Date and Time
% D	The day of the month (01-31)
% H	Hours in the 24-hour system (00-23)
% I	Hours in the 12-hour system (01-12)
% J	Day of the year (001-366)
% M	Minute (00-59)
% M	Month (01-12)
% P	"Am" or "PM )"
% S	Seconds (00-59)
% W	The day of the week (0-6 is equivalent to Sunday-Saturday)
% X	Date, for example
% X	Time, such as 23:48:20
% Y	Two-digit year (00-99)
% Y	Complete year (2012)
%	Character '%'

Print (OS. date ("% Y-% m-% d "))-- Output
The description of the CPU time returned by the function OS. Clock (), which is usually used to calculate a period of time.CodeExecution efficiency. For example:

 1   Local X = OS. Clock ()
 2   Local S = 0 
 3   For I = 1 , 10000000   Do  
 4 S = S + I
 5   End 
 6   Print ( String. Format ( "  Elapsed time: %. 2f \ n  " , OS. Clock ()-X ))
 7  
 8   --  Output result: 
  9   --  Elapsed time: 0.21 

2. Other system calls:
FunctionOS. Exit ()Can abort the currentProgram. FunctionOS. getenv ()Obtains the value of an environment variable. For example:
Print (OS. getenv ("path "))-- If the environment variable does not exist, Nil is returned.
OS .exe cuteThe function is used to execute commands related to the operating system, such:
OS .exe cute ("mkdir" .. "hello ")