The vSphere SDK for Perl provides an easy-to-use Perl scripting interface to
the vSphere API. SDK ships with utilities, and documentation for building
vSphere management applications.

The vSphere Command-Line Interface (vSphere CLI) command set allows you to 
run common system administration commands against ESX/ESXi systems from any 
machine with network access to those systems. You can also run most vSphere 
CLI commands against a vCenter Server system and target any ESX/ESXi system 
that vCenter Server system manages.

vSphere CLI commands are especially useful for ESXi hosts because ESXi does 
not include a service console.

WWW: http://downloads.vmware.com/d/info/datacenter_downloads/vmware_vsphere_4/