Q:\>perl -w -MO=Deparse -e "s;;new;;old;;g"
Unquoted string "old" may clash with future reserved word at -e line 1.
Unquoted string "g" may clash with future reserved word at -e line 1.
Useless use of a constant in void context at -e line 1.
Useless use of a constant in void context at -e line 1.
BEGIN { $^W = 1; }
s//new/;
'???';
'???';
-e syntax OK