How to get substring between two strings in DART?

You can use String.indexOf combined with String.substring:

void main() {
  const str = "the quick brown fox jumps over the lazy dog";
  const start = "quick";
  const end = "over";

  final startIndex = str.indexOf(start);
  final endIndex = str.indexOf(end, startIndex + start.length);

  print(str.substring(startIndex + start.length, endIndex)); // brown fox jumps
}

Note also that the startIndex is inclusive, while the endIndex is exclusive.

final str = 'the quick brown fox jumps over the lazy dog';
final start = 'quick';
final end = 'over';

final startIndex = str.indexOf(start);
final endIndex = str.indexOf(end);
final result = str.substring(startIndex + start.length, endIndex).trim();

I love regexp with lookbehind (?<...) and lookahead (?=...):

void main() {
  var re = RegExp(r'(?<=quick)(.*)(?=over)');
  String data = "the quick brown fox jumps over the lazy dog";
  var match = re.firstMatch(data);
  if (match != null) print(match.group(0));
}