--exclude-existing[=<pattern>]::
Make 'git show-ref' act as a filter that reads refs from stdin of the
- form "^(?:<anything>\s)?<refname>(?:\^\{\})?$" and performs the
- following actions on each:
+ form "^(?:<anything>\s)?<refname>(?:{backslash}{caret}\{\})?$"
+ 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;