[SOLVED] How to download Proxmox 4.2 on the command line?

You need to escape it. The ampersand's (&) have to be escaped in your shell. This can be easily done by "" around:

Code:
$ /tmp > wget "http://www.proxmox.com/en/downloads?task=callelement&format=raw&item_id=188&element=f85c494b-2b32-4109-b8c1-083cca2b7db6&method=download&args[0]=8974fa38125a347c7eb19965997f99b9"

--2016-05-31 22:27:56--  http://www.proxmox.com/en/downloads?task=callelement&format=raw&item_id=188&element=f85c494b-2b32-4109-b8c1-083cca2b7db6&method=download&args[0]=8974fa38125a347c7eb19965997f99b9
Resolving www.proxmox.com... 51.254.68.58
Connecting to www.proxmox.com|51.254.68.58|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 733247488 (699M) [application/x-cd-image]
Saving to: 'downloads?task=callelement&format=raw&item_id=188&element=f85c494b-2b32-4109-b8c1-083cca2b7db6&method=download&args[0]=8974fa38125a347c7eb19965997f99b9'

oads?task=callelement&fo   0%[                                   ]   2.30M   667KB/s    eta 17m 52s
^C