posix.pod

UNIX下perl实现代码

Returns the value of the specified enironment variable.
The same information is available through the C<%ENV> array.

=item geteuid

Returns the effective user identifier.  Identical to Perl's builtin C<$E<gt>>
variable, see L<perlvar/$EUID>.

=item getgid

Returns the user's real group identifier.  Similar to Perl's builtin
variable C<$)>, see L<perlvar/$GID>.

=item getgrgid

This is identical to Perl's builtin C<getgrgid()> function for
returning group entries by group identifiers, see
L<perlfunc/getgrgid>.

=item getgrnam

This is identical to Perl's builtin C<getgrnam()> function for
returning group entries by group names, see L<perlfunc/getgrnam>.

=item getgroups

Returns the ids of the user's supplementary groups.  Similar to Perl's
builtin variable C<$)>, see L<perlvar/$GID>.

=item getlogin

This is identical to Perl's builtin C<getlogin()> function for
returning the user name associated with the current session, see
L<perlfunc/getlogin>.

=item getpgrp

This is identical to Perl's builtin C<getpgrp()> function for
returning the prcess group identifier of the current process, see
L<perlfunc/getpgrp>.

=item getpid

Returns the process identifier.  Identical to Perl's builtin
variable C<$$>, see L<perlvar/$PID>.

=item getppid

This is identical to Perl's builtin C<getppid()> function for
returning the process identifier of the parent process of the current
process , see L<perlfunc/getppid>.

=item getpwnam

This is identical to Perl's builtin C<getpwnam()> function for
returning user entries by user names, see L<perlfunc/getpwnam>.

=item getpwuid

This is identical to Perl's builtin C<getpwuid()> function for
returning user entries by user identifiers, see L<perlfunc/getpwuid>.

=item gets

Returns one line from C<STDIN>, similar to E<lt>E<gt>, also known
as the C<readline()> function, see L<perlfunc/readline>.

B<NOTE>: if you have C programs that still use C<gets()>, be very
afraid.  The C<gets()> function is a source of endless grief because
it has no buffer overrun checks.  It should B<never> be used.  The
C<fgets()> function should be preferred instead.

=item getuid

Returns the user's identifier.  Identical to Perl's builtin C<$E<lt>> variable,
see L<perlvar/$UID>.

=item gmtime

This is identical to Perl's builtin C<gmtime()> function for
converting seconds since the epoch to a date in Greenwich Mean Time,
see L<perlfunc/gmtime>.

=item isalnum

This is identical to the C function, except that it can apply to a single
character or to a whole string.  Consider using regular expressions and the
C</[[:isalnum:]]/> construct instead, or possibly the C</\w/> construct.

=item isalpha

This is identical to the C function, except that it can apply to a single
character or to a whole string.  Consider using regular expressions and the
C</[[:isalpha:]]/> construct instead.

=item isatty

Returns a boolean indicating whether the specified filehandle is connected
to a tty.  Similar to the C<-t> operator, see L<perlfunc/-X>.

=item iscntrl

This is identical to the C function, except that it can apply to a single
character or to a whole string.  Consider using regular expressions and the
C</[[:iscntrl:]]/> construct instead.

=item isdigit

This is identical to the C function, except that it can apply to a single
character or to a whole string.  Consider using regular expressions and the
C</[[:isdigit:]]/> construct instead, or the C</\d/> construct.

=item isgraph

This is identical to the C function, except that it can apply to a single
character or to a whole string.  Consider using regular expressions and the
C</[[:isgraph:]]/> construct instead.

=item islower

This is identical to the C function, except that it can apply to a single
character or to a whole string.  Consider using regular expressions and the
C</[[:islower:]]/> construct instead.  Do B<not> use C</a-z/>.

=item isprint

This is identical to the C function, except that it can apply to a single
character or to a whole string.  Consider using regular expressions and the
C</[[:isprint:]]/> construct instead.

=item ispunct

This is identical to the C function, except that it can apply to a single
character or to a whole string.  Consider using regular expressions and the
C</[[:ispunct:]]/> construct instead.

=item isspace

This is identical to the C function, except that it can apply to a single
character or to a whole string.  Consider using regular expressions and the
C</[[:isspace:]]/> construct instead, or the C</\s/> construct.

=item isupper

This is identical to the C function, except that it can apply to a single
character or to a whole string.  Consider using regular expressions and the
C</[[:isupper:]]/> construct instead.  Do B<not> use C</A-Z/>.

=item isxdigit

This is identical to the C function, except that it can apply to a single
character or to a whole string.  Consider using regular expressions and the
C</[[:isxdigit:]]/> construct instead, or simply C</[0-9a-f]/i>.

=item kill

This is identical to Perl's builtin C<kill()> function for sending
signals to processes (often to terminate them), see L<perlfunc/kill>.

=item labs

(For returning absolute values of long integers.)
labs() is C-specific, see L<perlfunc/abs> instead.

=item ldexp

This is identical to the C function C<ldexp()>
for multiplying floating point numbers with powers of two.

	$x_quadrupled = POSIX::ldexp($x, 2);

=item ldiv

(For computing dividends of long integers.)
ldiv() is C-specific, use C</> and C<int()> instead.

=item link

This is identical to Perl's builtin C<link()> function
for creating hard links into files, see L<perlfunc/link>.

=item localeconv

Get numeric formatting information.  Returns a reference to a hash
containing the current locale formatting values.

Here is how to query the database for the B<de> (Deutsch or German) locale.

	$loc = POSIX::setlocale( &POSIX::LC_ALL, "de" );
	print "Locale = $loc\n";
	$lconv = POSIX::localeconv();
	print "decimal_point	= ", $lconv->{decimal_point},	"\n";
	print "thousands_sep	= ", $lconv->{thousands_sep},	"\n";
	print "grouping	= ", $lconv->{grouping},	"\n";
	print "int_curr_symbol	= ", $lconv->{int_curr_symbol},	"\n";
	print "currency_symbol	= ", $lconv->{currency_symbol},	"\n";
	print "mon_decimal_point = ", $lconv->{mon_decimal_point}, "\n";
	print "mon_thousands_sep = ", $lconv->{mon_thousands_sep}, "\n";
	print "mon_grouping	= ", $lconv->{mon_grouping},	"\n";
	print "positive_sign	= ", $lconv->{positive_sign},	"\n";
	print "negative_sign	= ", $lconv->{negative_sign},	"\n";
	print "int_frac_digits	= ", $lconv->{int_frac_digits},	"\n";
	print "frac_digits	= ", $lconv->{frac_digits},	"\n";
	print "p_cs_precedes	= ", $lconv->{p_cs_precedes},	"\n";
	print "p_sep_by_space	= ", $lconv->{p_sep_by_space},	"\n";
	print "n_cs_precedes	= ", $lconv->{n_cs_precedes},	"\n";
	print "n_sep_by_space	= ", $lconv->{n_sep_by_space},	"\n";
	print "p_sign_posn	= ", $lconv->{p_sign_posn},	"\n";
	print "n_sign_posn	= ", $lconv->{n_sign_posn},	"\n";

=item localtime

This is identical to Perl's builtin C<localtime()> function for
converting seconds since the epoch to a date see L<perlfunc/localtime>.

=item log

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

=item log10

This is identical to the C function C<log10()>,
returning the 10-base logarithm of the numerical argument.
You can also use

    sub log10 { log($_[0]) / log(10) }

or

    sub log10 { log($_[0]) / 2.30258509299405 }  

or

    sub log10 { log($_[0]) * 0.434294481903252 }

=item longjmp

longjmp() is C-specific: use L<perlfunc/die> instead.

=item lseek

Move the file's read/write position.  This uses file descriptors such as
those obtained by calling C<POSIX::open>.

	$fd = POSIX::open( "foo", &POSIX::O_RDONLY );
	$off_t = POSIX::lseek( $fd, 0, &POSIX::SEEK_SET );

Returns C<undef> on failure.

=item malloc

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

=item mblen

This is identical to the C function C<mblen()>.
Perl does not have any support for the wide and multibyte
characters of the C standards, so this might be a rather 
useless function.

=item mbstowcs

This is identical to the C function C<mbstowcs()>.
Perl does not have any support for the wide and multibyte
characters of the C standards, so this might be a rather 
useless function.

=item mbtowc

This is identical to the C function C<mbtowc()>.
Perl does not have any support for the wide and multibyte
characters of the C standards, so this might be a rather 
useless function.

=item memchr

memchr() is C-specific, see L<perlfunc/index> instead.

=item memcmp

memcmp() is C-specific, use C<eq> instead, see L<perlop>.

=item memcpy

memcpy() is C-specific, use C<=>, see L<perlop>, or see L<perlfunc/substr>.

=item memmove

memmove() is C-specific, use C<=>, see L<perlop>, or see L<perlfunc/substr>.

=item memset

memset() is C-specific, use C<x> instead, see L<perlop>.

=item mkdir

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

=item mkfifo

This is similar to the C function C<mkfifo()> for creating
FIFO special files.

	if (mkfifo($path, $mode)) { ....

Returns C<undef> on failure.  The C<$mode> is similar to the
mode of C<mkdir()>, see L<perlfunc/mkdir>.

=item mktime

Convert date/time info to a calendar time.

Synopsis:

	mktime(sec, min, hour, mday, mon, year, wday = 0, yday = 0, isdst = 0)

The month (C<mon>), weekday (C<wday>), and yearday (C<yday>) begin at zero.
I.e. January is 0, not 1; Sunday is 0, not 1; January 1st is 0, not 1.  The
year (C<year>) is given in years since 1900.  I.e. The year 1995 is 95; the
year 2001 is 101.  Consult your system's C<mktime()> manpage for details
about these and the other arguments.

Calendar time for December 12, 1995, at 10:30 am.

	$time_t = POSIX::mktime( 0, 30, 10, 12, 11, 95 );
	print "Date = ", POSIX::ctime($time_t);

Returns C<undef> on failure.

=item modf

Return the integral and fractional parts of a floating-point number.

	($fractional, $integral) = POSIX::modf( 3.14 );

=item nice

This is similar to the C function C<nice()>, for changing
the scheduling preference of the current process.  Positive
arguments mean more polite process, negative values more
needy process.  Normal user processes can only be more polite.

Returns C<undef> on failure.

=item offsetof

offsetof() is C-specific, you probably want to see L<perlfunc/pack> instead.

=item open

Open a file for reading for writing.  This returns file descriptors, not
Perl filehandles.  Use C<POSIX::close> to close the file.

Open a file read-only with mode 0666.

	$fd = POSIX::open( "foo" );

Open a file for read and write.

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

Open a file for write, with truncation.

	$fd = POSIX::open( "foo", &POSIX::O_WRONLY | &POSIX::O_TRUNC );

Create a new file with mode 0640.  Set up the file for writing.

	$fd = POSIX::open( "foo", &POSIX::O_CREAT | &POSIX::O_WRONLY, 0640 );

Returns C<undef> on failure.

See also L<perlfunc/sysopen>.

=item opendir

Open a directory for reading.

	$dir = POSIX::opendir( "/tmp" );
	@files = POSIX::readdir( $dir );
	POSIX::closedir( $dir );

Returns C<undef> on failure.

=item pathconf

Retrieves the value of a configurable limit on a file or directory.

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

	$path_max = POSIX::pathconf( "/tmp", &POSIX::_PC_PATH_MAX );

Returns C<undef> on failure.

=item pause

This is similar to the C function C<pause()>, which suspends
the execution of the current process until a signal is received.

Returns C<undef> on failure.

=item perror

This is identical to the C function C<perror()>, which outputs to the
standard error stream the specified message followed by ": " and the
current error string.  Use the C<warn()> function and the C<$!>
variable instead, see L<perlfunc/warn> and L<perlvar/$ERRNO>.

=item pipe

Create an interprocess channel.  This returns file descriptors like those
returned by C<POSIX::open>.

	($fd0, $fd1) = POSIX::pipe();
	POSIX::write( $fd0, "hello", 5 );
	POSIX::read( $fd1, $buf, 5 );

See also L<perlfunc/pipe>.

=item pow

Computes C<$x> raised to the power C<$exponent>.

	$ret = POSIX::pow( $x, $exponent );

You can also use the C<**> operator, see L<perlop>.

=item printf

Formats and prints the specified arguments to STDOUT.
See also L<perlfunc/printf>.

=item putc

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

=item putchar

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

=item puts

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

=item qsort

qsort() is C-specific, see L<perlfunc/sort> instead.

=item raise

Sends the specified signal to the current process.
See also L<perlfunc/kill> and the C<$$> in L<perlvar/$PID>.

=item rand

C<rand()> is non-portable, see L<perlfunc/rand> instead.

=item read

Read from a file.  This uses file descriptors such as those obtained by
calling C<POSIX::open>.  If the buffer C<$buf> is not large enough for the
read then Perl will extend it to make room for the request.

	$fd = POSIX::open( "foo", &POSIX::O_RDONLY );
	$bytes = POSIX::read( $fd, $buf, 3 );

Returns C<undef> on failure.

See also L<perlfunc/sysread>.

=item readdir

This is identical to Perl's builtin C<readdir()> function
for reading directory entries, see L<perlfunc/readdir>.

=item realloc

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

=item remove

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

=item rename

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

=item rewind

Seeks to the beginning of the file.

=item rewinddir