my @tests = (
  '"abcd\\\\efgh"',
  '"abcd\\""',
  '"abcd\\"efgh"',
  '"abcd\\\\\\"efgh"',
  '"abcd\\\\i\\"efgh"',
  '"abcd\\\\"',
);

foreach my $test (@tests) {
  print "Try for \"$test\":\n";
  if ($test =~ /^"((?:[^"\\]|\\["\\])+)"$/) {
    print "It matches!\n";
    print '$1: ' . $1 . "\n";
    print '$2: ' . (defined($2) ? "\$2 is defined\n" : "\$2 is NOT defined\n");
  } else {
    print "It does not match!\n";
  }
  print "\n";
}

##</code><code>##

Try for ""abcd\\efgh"":
It matches!
$1: abcd\\efgh
$2: $2 is NOT defined

Try for ""abcd\""":
It matches!
$1: abcd\"
$2: $2 is NOT defined

Try for ""abcd\"efgh"":
It matches!
$1: abcd\"efgh
$2: $2 is NOT defined

Try for ""abcd\\\"efgh"":
It matches!
$1: abcd\\\"efgh
$2: $2 is NOT defined

Try for ""abcd\\i\"efgh"":
It matches!
$1: abcd\\i\"efgh
$2: $2 is NOT defined

Try for ""abcd\\"":
It matches!
$1: abcd\\
$2: $2 is NOT defined