You can if you [precede the tag in the search with a minus (-)][1]:

    shell [cmd] -[linux]

The following links pop for searches across the SOFU for questions that mention *shell* tagged  [tag:cmd] but **not** tagged [tag:linux].

StackOverflow: http://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


  [1]: https://meta.stackexchange.com/questions/16462/can-i-do-complex-tag-searches