Como terminar un proceso con Perl

Pues con kill.
kill ( 'SIGNAL' , PID );

Lista de señales:

Signal	Number	Description
SIGHUP	1	On hangup
SIGINT	2	On interrupt
SIGQUIT	3	On Quit key
SIGILL	4	Illegal instruction
SIGTRAP	5	Trap instruction
SIGABRT	6	Abort message
SIGIOT	6	Input/output transfer
SIGBUS	7	Bus error
SIGFPE	8	Floating-point error
SIGKILL	9	Kill signal from system
SIGUSR1	10	User defined
SIGSEGV	11	Segmentation violation
SIGUSR2	12	User defined
SIGPIPE	13	Pipe fault (broken pipe)
SIGALRM	14	Alarm
SIGTERM	15	Termination
SIGSTKFLT	16	Stack fault
SIGchLD	17	Signal from child
SIGCONT	18	Continuing a stopped process
SIGSTOP	19	Stopping a process
SIGTSTP	20	Stopping a process from terminal
SIGTTIN	21	Stopping a process reading from controlling terminal
SIGTTOU	22	Stopping a process writing to controlling terminal
SIGURG	23	Urgent condition
SIGXCPU	24	Excessive CPU limits reached
SIGXFSZ	25	Excessive file size limits reached
SIGVTALRM	26	Virtual interval timer expired
SIGPROF	27	Profiling interval timer expired
SIGWINch	28	Window size changed by background process
SIGIO	29	Asynchronous I/O
SIGPWR	30	Power failure
SIGUNUSED	31	Unused

ejemplo:
kill ('KILL' , $PID);

REF:
http://ods.com.ua/win/eng/program/Perl5Unleashed/ch14.phtml#Signals