use strict;
use warnings;
use Data::Dumper;

sub makeAServerdown
{
print "AHA:", @_, "\n";
}

my $line = 'task=B pretask=makeAServerdown posttask=checkBServer';

my $h = { map { my ($k,$v) = split /=/; $k=>$v } split (' ', $line) };

print Dumper $h;

{
  no strict 'refs';
  $h->{pretask}->($h->{task});
}
__END__
$VAR1 = {
          'pretask' => 'makeAServerdown',
          'task' => 'B',
          'posttask' => 'checkBServer'
        };
AHA:B