posix.pod

UNIX下perl实现代码

=head1 NAME

POSIX - Perl interface to IEEE Std 1003.1

=head1 SYNOPSIS

    use POSIX;
    use POSIX qw(setsid);
    use POSIX qw(:errno_h :fcntl_h);

    printf "EINTR is %d\n", EINTR;

    $sess_id = POSIX::setsid();

    $fd = POSIX::open($path, O_CREAT|O_EXCL|O_WRONLY, 0644);
	# note: that's a filedescriptor, *NOT* a filehandle

=head1 DESCRIPTION

The POSIX module permits you to access all (or nearly all) the standard
POSIX 1003.1 identifiers.  Many of these identifiers have been given Perl-ish
interfaces.  Things which are C<#defines> in C, like EINTR or O_NDELAY, are
automatically exported into your namespace.  All functions are only exported
if you ask for them explicitly.  Most likely people will prefer to use the
fully-qualified function names.

This document gives a condensed list of the features available in the POSIX
module.  Consult your operating system's manpages for general information on
most features.  Consult L<perlfunc> for functions which are noted as being
identical to Perl's builtin functions.

The first section describes POSIX functions from the 1003.1 specification.
The second section describes some classes for signal objects, TTY objects,
and other miscellaneous objects.  The remaining sections list various
constants and macros in an organization which roughly follows IEEE Std
1003.1b-1993.

=head1 NOTE

The POSIX module is probably the most complex Perl module supplied with
the standard distribution.  It incorporates autoloading, namespace games,
and dynamic loading of code that's in Perl, C, or both.  It's a great
source of wisdom.

=head1 CAVEATS 

A few functions are not implemented because they are C specific.  If you
attempt to call these, they will print a message telling you that they
aren't implemented, and suggest using the Perl equivalent should one
exist.  For example, trying to access the setjmp() call will elicit the
message "setjmp() is C-specific: use eval {} instead".

Furthermore, some evil vendors will claim 1003.1 compliance, but in fact
are not so: they will not pass the PCTS (POSIX Compliance Test Suites).
For example, one vendor may not define EDEADLK, or the semantics of the
errno values set by open(2) might not be quite right.  Perl does not
attempt to verify POSIX compliance.  That means you can currently
successfully say "use POSIX",  and then later in your program you find
that your vendor has been lax and there's no usable ICANON macro after
all.  This could be construed to be a bug.

=head1 FUNCTIONS

=over 8

=item _exit

This is identical to the C function C<_exit()>.  It exits the program
immediately which means among other things buffered I/O is B<not> flushed.

=item abort

This is identical to the C function C<abort()>.  It terminates the
process with a C<SIGABRT> signal unless caught by a signal handler or
if the handler does not return normally (it e.g.  does a C<longjmp>).

=item abs

This is identical to Perl's builtin C<abs()> function, returning
the absolute value of its numerical argument.

=item access

Determines the accessibility of a file.

	if( POSIX::access( "/", &POSIX::R_OK ) ){
		print "have read permission\n";
	}

Returns C<undef> on failure.  Note: do not use C<access()> for
security purposes.  Between the C<access()> call and the operation
you are preparing for the permissions might change: a classic
I<race condition>.

=item acos

This is identical to the C function C<acos()>, returning
the arcus cosine of its numerical argument.  See also L<Math::Trig>.

=item alarm

This is identical to Perl's builtin C<alarm()> function,
either for arming or disarming the C<SIGARLM> timer.

=item asctime

This is identical to the C function C<asctime()>.  It returns
a string of the form

	"Fri Jun  2 18:22:13 2000\n\0"

and it is called thusly

	$asctime = asctime($sec, $min, $hour, $mday, $mon, $year,
			   $wday, $yday, $isdst);

The C<$mon> is zero-based: January equals C<0>.  The C<$year> is
1900-based: 2001 equals C<101>.  The C<$wday>, C<$yday>, and C<$isdst>
default to zero (and the first two are usually ignored anyway).

=item asin

This is identical to the C function C<asin()>, returning
the arcus sine of its numerical argument.  See also L<Math::Trig>.

=item assert

Unimplemented, but you can use L<perlfunc/die> and the L<Carp> module
to achieve similar things.

=item atan

This is identical to the C function C<atan()>, returning the
arcus tangent of its numerical argument.  See also L<Math::Trig>.

=item atan2

This is identical to Perl's builtin C<atan2()> function, returning
the arcus tangent defined by its two numerical arguments, the I<y>
coordinate and the I<x> coordinate.  See also L<Math::Trig>.

=item atexit

atexit() is C-specific: use C<END {}> instead, see L<perlsub>.

=item atof

atof() is C-specific.  Perl converts strings to numbers transparently.
If you need to force a scalar to a number, add a zero to it.

=item atoi

atoi() is C-specific.  Perl converts strings to numbers transparently.
If you need to force a scalar to a number, add a zero to it.
If you need to have just the integer part, see L<perlfunc/int>.

=item atol

atol() is C-specific.  Perl converts strings to numbers transparently.
If you need to force a scalar to a number, add a zero to it.
If you need to have just the integer part, see L<perlfunc/int>.

=item bsearch

bsearch() not supplied.  For doing binary search on wordlists,
see L<Search::Dict>.

=item calloc

calloc() is C-specific.  Perl does memory management transparently.

=item ceil

This is identical to the C function C<ceil()>, returning the smallest
integer value greater than or equal to the given numerical argument.

=item chdir

This is identical to Perl's builtin C<chdir()> function, allowing
one to change the working (default) directory, see L<perlfunc/chdir>.

=item chmod

This is identical to Perl's builtin C<chmod()> function, allowing
one to change file and directory permissions, see L<perlfunc/chmod>.

=item chown

This is identical to Perl's builtin C<chown()> function, allowing one
to change file and directory owners and groups, see L<perlfunc/chown>.

=item clearerr

Use the method L<IO::Handle::clearerr()> instead, to reset the error
state (if any) and EOF state (if any) of the given stream.

=item clock

This is identical to the C function C<clock()>, returning the
amount of spent processor time in microseconds.

=item close

Close the file.  This uses file descriptors such as those obtained by calling
C<POSIX::open>.

	$fd = POSIX::open( "foo", &POSIX::O_RDONLY );
	POSIX::close( $fd );

Returns C<undef> on failure.

See also L<perlfunc/close>.

=item closedir

This is identical to Perl's builtin C<closedir()> function for closing
a directory handle, see L<perlfunc/closedir>.

=item cos

This is identical to Perl's builtin C<cos()> function, for returning
the cosine of its numerical argument, see L<perlfunc/cos>.
See also L<Math::Trig>.

=item cosh

This is identical to the C function C<cosh()>, for returning
the hyperbolic cosine of its numeric argument.  See also L<Math::Trig>.

=item creat

Create a new file.  This returns a file descriptor like the ones returned by
C<POSIX::open>.  Use C<POSIX::close> to close the file.

	$fd = POSIX::creat( "foo", 0611 );
	POSIX::close( $fd );

See also L<perlfunc/sysopen> and its C<O_CREAT> flag.

=item ctermid

Generates the path name for the controlling terminal.

	$path = POSIX::ctermid();

=item ctime

This is identical to the C function C<ctime()> and equivalent
to C<asctime(localtime(...))>, see L</asctime> and L</localtime>.

=item cuserid

Get the login name of the owner of the current process.

	$name = POSIX::cuserid();

=item difftime

This is identical to the C function C<difftime()>, for returning
the time difference (in seconds) between two times (as returned
by C<time()>), see L</time>.

=item div

div() is C-specific, use L<perlfunc/int> on the usual C</> division and
the modulus C<%>.

=item dup

This is similar to the C function C<dup()>, for duplicating a file
descriptor.

This uses file descriptors such as those obtained by calling
C<POSIX::open>.

Returns C<undef> on failure.

=item dup2

This is similar to the C function C<dup2()>, for duplicating a file
descriptor to an another known file descriptor.

This uses file descriptors such as those obtained by calling
C<POSIX::open>.

Returns C<undef> on failure.

=item errno

Returns the value of errno.

	$errno = POSIX::errno();

This identical to the numerical values of the C<$!>, see L<perlvar/$ERRNO>.

=item execl

execl() is C-specific, see L<perlfunc/exec>.

=item execle

execle() is C-specific, see L<perlfunc/exec>.

=item execlp

execlp() is C-specific, see L<perlfunc/exec>.

=item execv

execv() is C-specific, see L<perlfunc/exec>.

=item execve

execve() is C-specific, see L<perlfunc/exec>.

=item execvp

execvp() is C-specific, see L<perlfunc/exec>.

=item exit

This is identical to Perl's builtin C<exit()> function for exiting the
program, see L<perlfunc/exit>.

=item exp

This is identical to Perl's builtin C<exp()> function for
returning the exponent (I<e>-based) of the numerical argument,
see L<perlfunc/exp>.

=item fabs

This is identical to Perl's builtin C<abs()> function for returning
the absolute value of the numerical argument, see L<perlfunc/abs>.

=item fclose

Use method C<IO::Handle::close()> instead, or see L<perlfunc/close>.

=item fcntl

This is identical to Perl's builtin C<fcntl()> function,
see L<perlfunc/fcntl>.

=item fdopen

Use method C<IO::Handle::new_from_fd()> instead, or see L<perlfunc/open>.

=item feof

Use method C<IO::Handle::eof()> instead, or see L<perlfunc/eof>.

=item ferror

Use method C<IO::Handle::error()> instead.

=item fflush

Use method C<IO::Handle::flush()> instead.
See also L<perlvar/$OUTPUT_AUTOFLUSH>.

=item fgetc

Use method C<IO::Handle::getc()> instead, or see L<perlfunc/read>.

=item fgetpos

Use method C<IO::Seekable::getpos()> instead, or see L<L/seek>.

=item fgets

Use method C<IO::Handle::gets()> instead.  Similar to E<lt>E<gt>, also known
as L<perlfunc/readline>.

=item fileno

Use method C<IO::Handle::fileno()> instead, or see L<perlfunc/fileno>.

=item floor

This is identical to the C function C<floor()>, returning the largest
integer value less than or equal to the numerical argument.

=item fmod

This is identical to the C function C<fmod()>.

	$r = modf($x, $y);

It returns the remainder C<$r = $x - $n*$y>, where C<$n = trunc($x/$y)>.
The C<$r> has the same sign as C<$x> and magnitude (absolute value)
less than the magnitude of C<$y>.

=item fopen

Use method C<IO::File::open()> instead, or see L<perlfunc/open>.

=item fork

This is identical to Perl's builtin C<fork()> function
for duplicating the current process, see L<perlfunc/fork>
and L<perlfork> if you are in Windows.

=item fpathconf

Retrieves the value of a configurable limit on a file or directory.  This
uses file descriptors such as those obtained by calling C<POSIX::open>.

The following will determine the maximum length of the longest allowable
pathname on the filesystem which holds C</tmp/foo>.

	$fd = POSIX::open( "/tmp/foo", &POSIX::O_RDONLY );
	$path_max = POSIX::fpathconf( $fd, &POSIX::_PC_PATH_MAX );

Returns C<undef> on failure.

=item fprintf

fprintf() is C-specific, see L<perlfunc/printf> instead.

=item fputc

fputc() is C-specific, see L<perlfunc/print> instead.

=item fputs

fputs() is C-specific, see L<perlfunc/print> instead.

=item fread

fread() is C-specific, see L<perlfunc/read> instead.

=item free

free() is C-specific.  Perl does memory management transparently.

=item freopen

freopen() is C-specific, see L<perlfunc/open> instead.

=item frexp

Return the mantissa and exponent of a floating-point number.

	($mantissa, $exponent) = POSIX::frexp( 1.234e56 );

=item fscanf

fscanf() is C-specific, use E<lt>E<gt> and regular expressions instead.

=item fseek

Use method C<IO::Seekable::seek()> instead, or see L<perlfunc/seek>.

=item fsetpos

Use method C<IO::Seekable::setpos()> instead, or seek L<perlfunc/seek>.

=item fstat

Get file status.  This uses file descriptors such as those obtained by
calling C<POSIX::open>.  The data returned is identical to the data from
Perl's builtin C<stat> function.

	$fd = POSIX::open( "foo", &POSIX::O_RDONLY );
	@stats = POSIX::fstat( $fd );

=item ftell

Use method C<IO::Seekable::tell()> instead, or see L<perlfunc/tell>.

=item fwrite

fwrite() is C-specific, see L<perlfunc/print> instead.

=item getc

This is identical to Perl's builtin C<getc()> function,
see L<perlfunc/getc>.

=item getchar

Returns one character from STDIN.  Identical to Perl's C<getc()>,
see L<perlfunc/getc>.

=item getcwd

Returns the name of the current working directory.
See also L<Cwd>.

=item getegid

Returns the effective group identifier.  Similar to Perl' s builtin
variable C<$(>, see L<perlvar/$EGID>.

=item getenv