How can you get the clipboard contents with a Windows command?
If you accept to use PowerShell (and not cmd) the you can use Get-Clipboard exactly as you was looking for.
Get-Clipboard > myfile.txtThe adventage of this method is that you have nothing to install.
Note: In place of clip you can use Set-Clipboard that has more options.
Note 2: If you really want to run it from cmd, you can call powershell as in the following example powershell -command "Get-Clipboard | sort | Set-Clipboard".
You can use the paste.exe software in order to paste text just like you are describing.
http://www.c3scripts.com/tutorials/msdos/paste.html
With it you can do:
paste | commandto paste the contents of the windows clipboard into the input of the specified command prompt
or
paste > filenameto paste the clipboard contents to the specified file.
Clarifying an answer from @Kpym:
powershell -command "Get-Clipboard" > file.txtThis directly answers the question without using a 3rd party tool.