What about running sth like that:

echo '
connect / as sysdba
\@your_script
exit' | svrmgrl 2>&1 >/dev/null

Reply:

The order of the redirection matters... redirect stdout to /dev/null,
then stderr to stdout. Otherwise you'll still get your error messages
displayed.

Reply to Reply:

Opsss... That's right.
It seems svrmgrl redirects all to stdout, so I did not pay sufficient
attention to that :-)