You need to type "cd", now you're trying to execute a directory ... Which doesn't work, this should work:
% cd /usr/ports
If you are using tcsh you can use implicitcd option ("set implicitcd" in
~/.tcshrc) so you don't have to type "cd", from
tcsh(1)
Code:
implicitcd (+)
If set, the shell treats a directory name typed as a command as
though it were a request to change to that directory. If set
to verbose, the change of directory is echoed to the standard
output. This behavior is inhibited in non-interactive shell
scripts, or for command strings with more than one word.
Changing directory takes precedence over executing a like-named
command, but it is done after alias substitutions. Tilde and
variable expansions work as expected.