Sends a signal to a list of processes. Returns the number of processes successfully signaled (which is not necessarily the same as the number actually killed).
SIGNAL may be either a signal name (a string) or a signal number. A signal
name may start with a SIG
prefix, thus FOO
and SIGFOO
refer 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 list of signal names supported by the current platform can be found in
$Config{sig_name}
, which is provided by the Config
module. See Config
for more details.
A negative signal name is the same as a negative signal number, killing process
groups instead of processes. For example, kill '-KILL', $pgrp
and
kill -9, $pgrp
will send SIGKILL
to 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 ZERO
(or SIGZZERO
),
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() 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.