See the current Perl documentation for shmwrite.

Here is our local, out-dated (pre-5.6) version:

shmwrite - write SysV shared memory


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. See also IPC::SysV documentation.