The title and problem description seem incompatible -- its unclear what is being asked

Consider this

$ perl -wle " { local *foo = sub { warn 6}; foo; } foo; "
Unquoted string "foo" may clash with future reserved word at -e line 1
+.
Unquoted string "foo" may clash with future reserved word at -e line 1
+.
Useless use of a constant ("foo") in void context at -e line 1.
Useless use of a constant ("foo") in void context at -e line 1.


$ perl -wle " { local *foo = sub { warn 6}; foo(); } foo(); "
6 at -e line 1.
Undefined subroutine &main::foo called at -e line 1.
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What is your question?