Not exactly WordPress related, but here's a short example using a `find` with a *directory* type and zero *maxdepth*:

    $ find /srv/users/serverpilot/apps/*/public/ \
    -type d \
    -maxdepth 0 \
    -exec /usr/local/bin/wp core update --path={} \;

or in a single line:

    $ find /srv/users/serverpilot/apps/*/public/ -type d -maxdepth 0 -exec /usr/local/bin/wp core update --path={} \;