Os Library Tutorial

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os.clock()

Return CPU time since Lua started in seconds.

> = os.clock()
11056.989

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

Return formatted date string, or table of time information. The format string has the same format as the C strftime() function.

TODO: insert info, examples and links to strftime()

List all params at http://www.cplusplus.com/reference/clibrary/ctime/strftime/

Simple example:

> = os.date("%d.%m.%Y")
06.10.2012

If the format string is "*t" a table is returned containing the time information, e.g,

> table.foreach(os.date('*t'), print)
hour    14
min     36
wday    1
year    2003
yday    124
month   5
sec     33
day     4
isdst   true

Above example using pairs() method:

> for k, v in pairs(os.date("*t")) do print(k, v) end
year    2012
day     1
min     54
wday    4
month   8
isdst   true
yday    214
sec     39
hour    14

If the format is preceeded by "!" the time is converted to Coordinated Universal Time, e.g.,

> table.foreach(os.date('!*t'), print)
hour    21
min     36
wday    1
year    2003
yday    124
month   5
sec     42
day     4
isdst   false

Above example using pairs() method:

> for k, v in pairs(os.date("!*t")) do print(k, v) end
year    2012
day     1
min     58
wday    4
month   8
isdst   false
yday    214
sec     39
hour    12

os.date() returns a string in the format MM/DD/YY HH:MM:SS.

> print(os.date())
08/16/05 10:22:32

Nowadays os.date() returns a string in different format:

> = os.date()
Wed Aug  1 15:00:47 2012

os.difftime(t2, t1)

Calculate the number of seconds between time t1 to time t2.

> t1 = os.time()
> -- wait a little while then type....
> = os.difftime(os.time(), t1)
31
> = os.difftime(os.time(), t1)
38

os.execute([command])

Execute an operating system shell command. This is like the C system() function. The system dependent status code is returned.

> = os.execute("echo hello")
hello
0
> = os.execute("mmmmm")  -- generate an error
'mmmmm' is not recognized as an internal or external command,
operable program or batch file.
1

With no argument, this command returns a non-zero value if an OS shell is presents or a zero value if one is not present.

> = os.execute()   -- no argument
1

os.exit([code])

Calls the C function exit, with an optional code, to terminate the host program. The default value for code is the success code.

> os.exit(0)   -- kill the Lua shell we are in and pass 0 back to parent shell

os.getenv(varname)

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

> = os.getenv("BANANA")
nil
> = os.getenv("USERNAME")
Nick

os.remove(filename)

Deletes the file with the given name. If this function fails, it returns nil, plus a string describing the error.

> os.execute("echo hello > banana.txt")
> = os.remove("banana.txt")
true
> = os.remove("banana.txt")
nil     banana.txt: No such file or directory   2

os.rename(oldname, newname)

Renames file named oldname to newname. If this function fails, it returns nil, plus a string describing the error.

> os.execute("echo hello > banana.txt")
> = os.rename("banana.txt", "apple.txt")
true
> = os.rename("banana.txt", "apple.txt")
nil     banana.txt: No such file or directory   2

os.setlocale(locale [, category])

Sets the current locale of the program. locale is a 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.

os.time([table])

Given a formatted date table, as used by os.date() return the time in system seconds.

> t = os.date('*t')  -- time now
> table.foreach(os.date('*t'), print)
hour    15
min     1
wday    1
year    2003
yday    124
month   5
sec     2
day     4
isdst   true
> = os.time(t)       -- time in system seconds
1052085659
> t.year = 2001      -- 2001, a Lua odyssey
> = os.time(t)       -- time then
989013659

os.tmpname ()

Generate a name that can be used for a temporary file. This only generates a name, it does not open a file.

> = os.tmpname()  -- on windows
\s2js.

> = os.tmpname()  -- on debian
/tmp/lua_5xPi18