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=item shmget KEY,SIZE,FLAGS

Calls the System V IPC function shmget.  Returns the shared memory
segment id, or the undefined value if there is an error.
See also L<perlipc/"SysV IPC"> and C<IPC::SysV> documentation.

=item shmread ID,VAR,POS,SIZE

=item shmwrite ID,STRING,POS,SIZE

Reads or writes the System V shared memory segment ID starting at
position POS for size SIZE by attaching to it, copying in/out, and
detaching from it.  When reading, VAR must be a variable that will
hold the data read.  When writing, if STRING is too long, only SIZE
bytes are used; if STRING is too short, nulls are written to fill out
SIZE bytes.  Return true if successful, or false if there is an error.
shmread() taints the variable. See also L<perlipc/"SysV IPC">,
C<IPC::SysV> documentation, and the C<IPC::Shareable> module from CPAN.

=item shutdown SOCKET,HOW

Shuts down a socket connection in the manner indicated by HOW, which
has the same interpretation as in the system call of the same name.

    shutdown(SOCKET, 0);    # I/we have stopped reading data
    shutdown(SOCKET, 1);    # I/we have stopped writing data
    shutdown(SOCKET, 2);    # I/we have stopped using this socket

This is useful with sockets when you want to tell the other
side you're done writing but not done reading, or vice versa.
It's also a more insistent form of close because it also
disables the file descriptor in any forked copies in other
processes.

=item sin EXPR

=item sin

Returns the sine of EXPR (expressed in radians).  If EXPR is omitted,
returns sine of C<$_>.

For the inverse sine operation, you may use the C<Math::Trig::asin>
function, or use this relation:

    sub asin { atan2($_[0], sqrt(1 - $_[0] * $_[0])) }

=item sleep EXPR

=item sleep

Causes the script to sleep for EXPR seconds, or forever if no EXPR.
May be interrupted if the process receives a signal such as C<SIGALRM>.
Returns the number of seconds actually slept.  You probably cannot
mix C<alarm> and C<sleep> calls, because C<sleep> is often implemented
using C<alarm>.

On some older systems, it may sleep up to a full second less than what
you requested, depending on how it counts seconds.  Most modern systems
always sleep the full amount.  They may appear to sleep longer than that,
however, because your process might not be scheduled right away in a
busy multitasking system.

For delays of finer granularity than one second, you may use Perl's
C<syscall> interface to access setitimer(2) if your system supports
it, or else see L</select> above.  The Time::HiRes module (from CPAN,
and starting from Perl 5.8 part of the standard distribution) may also
help.

See also the POSIX module's C<pause> function.

=item socket SOCKET,DOMAIN,TYPE,PROTOCOL

Opens a socket of the specified kind and attaches it to filehandle
SOCKET.  DOMAIN, TYPE, and PROTOCOL are specified the same as for
the system call of the same name.  You should C<use Socket> first
to get the proper definitions imported.  See the examples in
L<perlipc/"Sockets: Client/Server Communication">.

On systems that support a close-on-exec flag on files, the flag will
be set for the newly opened file descriptor, as determined by the
value of $^F.  See L<perlvar/$^F>.

=item socketpair SOCKET1,SOCKET2,DOMAIN,TYPE,PROTOCOL

Creates an unnamed pair of sockets in the specified domain, of the
specified type.  DOMAIN, TYPE, and PROTOCOL are specified the same as
for the system call of the same name.  If unimplemented, yields a fatal
error.  Returns true if successful.

On systems that support a close-on-exec flag on files, the flag will
be set for the newly opened file descriptors, as determined by the value
of $^F.  See L<perlvar/$^F>.

Some systems defined C<pipe> in terms of C<socketpair>, in which a call
to C<pipe(Rdr, Wtr)> is essentially:

    use Socket;
    socketpair(Rdr, Wtr, AF_UNIX, SOCK_STREAM, PF_UNSPEC);
    shutdown(Rdr, 1);        # no more writing for reader
    shutdown(Wtr, 0);        # no more reading for writer

See L<perlipc> for an example of socketpair use.  Perl 5.8 and later will
emulate socketpair using IP sockets to localhost if your system implements
sockets but not socketpair.

=item sort SUBNAME LIST

=item sort BLOCK LIST

=item sort LIST

In list context, this sorts the LIST and returns the sorted list value.
In scalar context, the behaviour of C<sort()> is undefined.

If SUBNAME or BLOCK is omitted, C<sort>s in standard string comparison
order.  If SUBNAME is specified, it gives the name of a subroutine
that returns an integer less than, equal to, or greater than C<0>,
depending on how the elements of the list are to be ordered.  (The C<<
<=> >> and C<cmp> operators are extremely useful in such routines.)
SUBNAME may be a scalar variable name (unsubscripted), in which case
the value provides the name of (or a reference to) the actual