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, false on error.
shmread() taints the variable. See also SysV IPC in perlipc,
IPC::SysV
, and the IPC::Shareable
module from CPAN.
Portability issues: shmread in perlport and shmwrite in perlport.