=head1 NAME

os - operating system facilities (standard library)

=head1 OVERVIEW

This library is implemented through table os.

=head1 REFERENCE

=head2 C<os.clock>

  os.clock ()

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

=head2 C<os.date>

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

Returns a string or a table containing date and time, formatted
according to the given string C<format>.

If the C<time> argument is present, this is the time to be formatted
(see the C<os.time> function for a description of this value).
Otherwise, C<date> formats the current time.

If C<format> starts with 'C<!>', then the date is formatted in
Coordinated Universal Time.  After this optional character, if
C<format> is C<*t>, then C<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)
  isdst (daylight saving flag, a boolean)

If C<format> is not C<*t>, then C<date> returns the date as a string,
formatted according to the same rules as the function
C<strftime>.

When called without arguments, C<date> returns a reasonable date and
time representation that depends on the host system and on the current
locale (that is, C<os.date()> is equivalent to C<os.date("%c")>).

=head2 C<os.difftime>

  os.difftime (t2, t1)

Returns the number of seconds from time C<t1> to time
C<t2>.  In POSIX, Windows, and some other systems, this
value is exactly C<t2>-C<t1>.

=head2 C<os.execute>

  os.execute ([command])

This function is equivalent to the function C<system>.  It
passes C<command> to be executed by an operating system shell.  It
returns a status code, which is system-dependent.  If C<command> is
absent, then it returns nonzero if a shell is available and zero
otherwise.

=head2 C<os.exit>

  os.exit ([code])

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

=head2 C<os.getenv>

  os.getenv (varname)

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

=head2 C<os.remove>

  os.remove (filename)

Deletes the file or directory with the given name.  Directories must
be empty to be removed.  If this function fails, it returns C<nil>,
plus a string describing the error.

=head2 C<os.rename>

  os.rename (oldname, newname)

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

=head2 C<os.setlocale>

  os.setlocale (locale [, category])

Sets the current locale of the program.

=over 4

=item C<locale>

is a string specifying a locale;

=item C<category>

is an optional string describing which category to change:
C<"all">, C<"collate">, C<"ctype">,
C<"monetary">, C<"numeric">, or C<"time">;

the default category is C<"all">.

=back

The function returns the name of the new locale, or C<nil> if the
request cannot be honored.

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

=head2 C<os.time>

  os.time ([table])

Returns the current time when called without arguments, or a time
representing the date and time specified by the given table.  This
table must have fields C<year>, C<month>, and C<day>, and may have
fields C<hour>, C<min>, C<sec>, and C<isdst> (for a description of
these fields, see the C<os.date> function).

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
C<time> can be used only as an argument to C<date> and C<difftime>.

=head2 C<os.tmpname>

  os.tmpname ()

Returns a string with a file name that can be used for a temporary
file.  The file must be explicitly opened before its use and
explicitly removed when no longer needed.

=head1 VERSION

This is Lua version 5.1.1.

=head1 CREDITS

Lua is developed at Lua.org, a laboratory of the Department of
Computer Science of PUC-Rio (the Pontifical Catholic University of Rio
de Janeiro in Brazil).  For more information about the authors, see
http://www.lua.org/authors.html .

=head1 LICENSE

Lua is licensed under the terms of the MIT license reproduced below.
This means that Lua is free software and can be used for both academic
and commercial purposes at absolutely no cost.

For details and rationale, see http://www.lua.org/license.html .

~~~~~

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~~~~~