San Fran — Writes to the shared memory segment ID starting at position pos for size size (by attaching to it, copying in, and detaching from it). If string is too long, only size bytes are used; if string is too short, nulls are written to fill out size bytes. The function returns true if successful or false if there is an error. On error, it puts the error code into $!. This function is available only on machines supporting System V IPC.