Kill a process from perl script

Question

I am trying to kill a process by name which i will pass as a variable to a system command.

Below is what i have:

my $processName=$ARGV[0];
print "$processName\n";
system(q/kill -9 `ps -ef | grep '$processName' | grep -v grep | awk '{print $2}'`/);

The above script throws an error:

kill: usage: kill [-s sigspec | -n signum | -sigspec] pid | jobspec ... or kill -l [sigspec]

However, if i directly enter the process name inside the system command, it works.

Can someone help me on this?

Answer 1

One problem is that the command line that invokes the script has the name of the process which you then query, by design; so one thing found will be the script itself.

This can be guarded against, but why go out to the system with that big pipeline?

Query the process in Perl, for example with Proc::ProcessTable

use warnings;
use strict;
use Proc::ProcessTable;

my $proc_name = shift // die "Usage: $0 process-name\n";  #/

my $pid;
my $pt = Proc::ProcessTable->new();
foreach my $proc (@{$pt->table}) {
    next if $proc->cmndline =~ /$0.*$proc_name/;  # not this script
    if ($proc->cmndline =~ /\Q$proc_name/) {
        $pid = $proc->pid;
        last;
    }   
}
die "Not found process with '$proc_name' in its name\n" if not defined $pid;    

kill 9, $pid;                    # must it be 9 (SIGKILL)? 
my $gone_pid = waitpid $pid, 0;  # then check that it's gone

Note that it is far nicer to "kill" a process by sending it SIGTERM (usually 15), not SIGKILL.

Looking for a process "name" can be perilous as there are many processes with long command lines running on a modern system that may contain that word. The code uses your requirement, to simply query by submitted name, but I recommend strengthening that with additional checks.

For many process details that the module can query see its stub module.

Even if you'd rather parse the process table yourself I would get only ps -ef and then parse it in the script. That gives far more flexibility in ensuring that you really terminate what you want.

Answer 2

You have the different variables $processName and $jobName, so the whole ` ` expression ends up empty. use strict would have pointed that out; it's useful even for three-line scripts. The kill error message is what you get when you run it without any arguments.

Pro tip: pkill exists, you can replace the whole problematic hack with one command.