You can, but AFAIK the way it does that is by overwriting the clipboard with null data. If you have a clipboard manager, it may save your credentials before it is overwritten so that it can retrieved later, and in this case, it is not something you want. Some clipboard managers can be clever and detect a null overwrite and interpret it as a request not to save the overwritten content.

Autotype do not suffer this problem and is generally considered safer. Some password managers have an even safer "mixed" mode where part of the password is in the clipboard and another part is auto-typed, meaning you have to monitor both the keyboard and the clipboard to grab the password

At least one possible fix would be a clipboard management standard such that an application can both set and clear or overwrite a specific clibpoard entry's data.

(I'd prefer the clear/overwrite myself.)

Another option would be specific IPC such that clipped content is available to one and only one other application or process. There was a recent HN submission on the Unix password manager utility "pass", including the ability to supply passwords to a command via shell expansion rather than as a command-line parameter. The former doesn't reveal the password in either process listings or shell history, the latter does.

That's a relatively primitive option, a more robust standard might also be provided.