my %pid;  # this should have global scope

sub start_proc
{
    my $proc = shift;  # use one sub for both jobs

    return if ( $pid{$proc} );  # already set means it's running

    $pid{$proc} = fork;
    if ( $pid{$proc} == 0 ) {   # true for the child process
        $path = ( $proc eq "email" ) ? $spam_dir : $check_dir;
        exec "perl $path/$proc.pl";
    }
# in the parent, $pid{$proc} is >0
}

sub stop_proc
{
    my $proc = shift;

    return unless ( $pid{$proc} );
    `kill -9 $pid{$proc}`;

    $pid{$proc} = 0;
}