use v5.36;
my %named_char= (
  a => "\a", b => "\b", t => "\t", n => "\n", v => chr(11), f => "\f"
);
my $line= <STDIN>;
if ($line =~ /
  ^"(           # starts with doublequote
    (?>               # no backtracking
      [^"\\]+             # allow any character other than \\ or "
    | \\[^xuU0-7]         # escaped character other than \x \u \U \0-7
    | \\[0-7]+            # octal escape
    | \\x[0-9a-fA-F]{1,2} # hex escape
    | \\u[0-9a-fA-F]{1,4} # unicode escape
    | \\U[0-9a-fA-F]{1,8} # 
    )*                # repeat as needed
  )"         # stop at next doublequote
/x) {
  my $literal= $1;
  my $op;
  $literal =~ s/\\(
     [^xuU0-7]          (?{ $op=sub{ $named_char{$1} || $1 } })
   | [0-7]+             (?{ $op=sub{ chr oct $1 } })
   | x[0-9a-fA-F]{1,2}  (?{ $op=sub{ chr hex substr $1,1 } })
   | u[0-9a-fA-F]{1,4}  (?{ $op=sub{ chr hex substr $1,1 } })
   | U[0-9a-fA-F]{1,8}  (?{ $op=sub{ chr hex substr $1,1 } })
   ) / &$op /xge;
  use DDP; p($literal);
}