To make it complete, here's a working code that reopen the STDOUT in the child process in order to avoid altogether the redirection in the command. Then, the exec do not spawn the shell.

#!/usr/bin/perl
use warnings;
use strict;

if (-f "./testfile") {
  !system "rm -f testfile"
    or die "Couldn't delete already present testfile\n";
}
my $pid;
my $parent = $$;
print "This is parent $parent \n";
defined($pid = fork) or die "Cannot fork: $!";
unless($pid)
  {
    print "This is child pid $$\n";
    open (STDOUT, '>', 'testfile') or die "Can't create testfile: $!";
    select STDOUT; $| = 1;

    my @cmd = qw(cat /dev/urandom);
    # Child process is here
    exec { $cmd[0] } @cmd;
  }
sleep 1;
kill 15 => $pid;
wait;
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