You can if you precede the tag in the search with a minus (-):
shell [cmd] -[linux]
The following links pop for searches across the SOFU for questions that mention shell tagged cmd but not tagged linux.
StackOverflow: https://stackoverflow.com/search?q=shell+%5Bcmd%5D+-%5Blinux%5D
ServerFault: https://serverfault.com/search?q=shell+%5Bcmd%5D+-%5Blinux%5D
SuperUser: https://superuser.com/search?q=shell+%5Bcmd%5D+-%5Blinux%5D
