+--exclude-existing, --exclude-existing=pattern::
+
+ Make git-show-ref act as a filter that reads refs from stdin of the
+ form "^(?:<anything>\s)?<refname>(?:\^\{\})?$" and performs the
+ following actions on each:
+ (1) strip "^{}" at the end of line if any;
+ (2) ignore if pattern is provided and does not head-match refname;
+ (3) warn if refname is not a well-formed refname and skip;
+ (4) ignore if refname is a ref that exists in the local repository;
+ (5) otherwise output the line.
+
+