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Flutter/Dart: Regex Replace with $2?

I'm trying to grab just the id number from a Facebook picture URL using the replaceall regex method in Dart. What should I be using instead of $2 in the following code? The id number I need is between the "asid=" and "&height".

void main() {
 String faceavatar = 'https://platform-lookaside.fbsbx.com/platform/profilepic/?asid=10153806530149154&height=50&width=50&ext=1596623207&hash=AeSi1yDvk8TCqZql';
      String currentavatar = faceavatar.replaceAll(RegExp('(.*asid=)(\d*)height.*'), $2;
  print(currentavatar);
}
Solution

  • You may try:

    .*?\basid\b=(\d+).*

    Explanation of the above regex:

    • .*? - Lazily matches everything except new-line before asid.
    • \basid\b - Matches asid literally. \b represents word boundary.
    • = - Matches = literally.
    • (\d+) - Represents first capturing group matching digits one or more times.
    • .* - Greedily everything except new-line zero or more times.
    • $1 - For the replacement part you can use $1 or match.group(1).

    Pictorial Representation

    You can find the demo of above regex in here.

    Sample Implementation in dart:

    void main() {
 String faceavatar = 'https://platform-lookaside.fbsbx.com/platform/profilepic/?asid=10153806530149154&height=50&width=50&ext=1596623207&hash=AeSi1yDvk8TCqZql';
      String currentavatar = faceavatar.replaceAllMapped(RegExp(r'.*?\basid\b=(\d+).*'), (match) {
  return '${match.group(1)}';
});
  print(currentavatar);
}

    You can find the sample run of the above implementation in here.