- kill SIGNAL, LIST
- kill SIGNAL
Sends a signal to a list of processes. Returns the number of arguments that were successfully used to signal (which is not necessarily the same as the number of processes actually killed, e.g. where a process group is killed).
SIGNAL may be either a signal name (a string) or a signal number. A signal name may start with a
SIGFOOrefer to the same signal. The string form of SIGNAL is recommended for portability because the same signal may have different numbers in different operating systems.
A negative signal name is the same as a negative signal number, killing process groups instead of processes. For example,
kill '-KILL', $pgrpand
kill -9, $pgrpwill send
SIGKILLto the entire process group specified. That means you usually want to use positive not negative signals.
If SIGNAL is either the number 0 or the string
SIGZERO), no signal is sent to the process, but kill checks whether it's possible to send a signal to it (that means, to be brief, that the process is owned by the same user, or we are the super-user). This is useful to check that a child process is still alive (even if only as a zombie) and hasn't changed its UID. See perlport for notes on the portability of this construct.
The behavior of kill when a PROCESS number is zero or negative depends on the operating system. For example, on POSIX-conforming systems, zero will signal the current process group, -1 will signal all processes, and any other negative PROCESS number will act as a negative signal number and kill the entire process group specified.
If both the SIGNAL and the PROCESS are negative, the results are undefined. A warning may be produced in a future version.
See Signals in perlipc for more details.
On some platforms such as Windows where the fork(2) system call is not available, Perl can be built to emulate fork at the interpreter level. This emulation has limitations related to kill that have to be considered, for code running on Windows and in code intended to be portable.
See perlfork for more details.
If there is no LIST of processes, no signal is sent, and the return value is 0. This form is sometimes used, however, because it causes tainting checks to be run. But see Laundering and Detecting Tainted Data in perlsec.
Portability issues: kill in perlport.