Backticks call a shell command and return its output. system just runs a command, letting its output go to the standard output. But you combined them into 
system `kill $pid`;

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So, backticks call kill. Kill doesn't return anything on the standard output, so system gets called with an empty string as the argument. Remove the backquotes and just call system: 

my $status = system 'kill', $pid;

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Update: Or, even better, use kill: 

kill $pid;

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لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ

In reply to Re: Killing processes by choroba
in thread Killing processes by deyaneria

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