Dart Requires Chilkat v11.1.0+

Regular Expression Replace Capture Groups

See more Regular Expressions Examples

Demonstrates replacing capture groups for a regular expression.

Note: Chilkat uses PCRE2. See PCRE2 Regular Expressions
Also see: PCRE2 Performance

Dart

import 'package:chilkat/chilkat.dart';

void main() {
  final subject = 'John Anders, +_+_+ Mary Robins \$\$\$\$';
  final pattern = '(?<first>\\w+)\\s+(?<last>\\w+)';

  final sb = CkStringBuilder();
  sb.append(subject);

  final json = CkJsonObject();
  json.emitCompact = false;

  final timeoutMs = 2000;
  var numMatches = sb.regexMatch(pattern, json, timeoutMs);
  if (numMatches < 0) {
    // Probably an error in the regular expression.
    // Suggestion: Use AI to help create and/or diagnose regular expressions.
    print(sb.lastErrorText);
    return;
  }

  // Examine the matches:
  print(json.emit());

  // There are 2 matches:

  // {
  //   "named": {
  //     "first": 1,
  //     "last": 2
  //   },
  //   "match": [
  //     {
  //       "group": [
  //         {
  //           "cap": "John Anders",
  //           "idx": 0,
  //           "len": 11
  //         },
  //         {
  //           "cap": "John",
  //           "idx": 0,
  //           "len": 4
  //         },
  //         {
  //           "cap": "Anders",
  //           "idx": 5,
  //           "len": 6
  //         }
  //       ]
  //     },
  //     {
  //       "group": [
  //         {
  //           "cap": "Mary Robins",
  //           "idx": 19,
  //           "len": 11
  //         },
  //         {
  //           "cap": "Mary",
  //           "idx": 19,
  //           "len": 4
  //         },
  //         {
  //           "cap": "Robins",
  //           "idx": 24,
  //           "len": 6
  //         }
  //       ]
  //     }
  //   ]
  // }

  // To replace capture groups, write code to examine each capture group within
  // each match, and provide a replacement string.
  // Then call RegexReplace.

  // For example, let's capitalize the first names, and add append "on" to the last name.
  // After doing replacements, we should get:  JOHN Anderson, +_+_+ MARY Robinson $$$$

  final firstNameIdx = json.intOf('named.first');
  final lastNameIdx = json.intOf('named.last');

  final sbTemp = CkStringBuilder();

  var i = 0;
  numMatches = json.sizeOfArray('match');
  while (i < numMatches) {

    json.i = i;

    // The replacement string for the first name will be all uppercase.
    json.j = firstNameIdx;
    sbTemp.clear();
    json.stringOfSb('match[i].group[j].cap', sbTemp);
    sbTemp.toUppercase();
    json.updateSb('match[i].group[j].rep', sbTemp);

    // Append "on" to the last name.
    json.j = lastNameIdx;
    sbTemp.clear();
    json.stringOfSb('match[i].group[j].cap', sbTemp);
    sbTemp.append('on');
    json.updateSb('match[i].group[j].rep', sbTemp);

    i++;
  }

  // The JSON now has replacement strings:
  print(json.emit());

  // {
  //   "named": {
  //     "first": 1,
  //     "last": 2
  //   },
  //   "match": [
  //     {
  //       "group": [
  //         {
  //           "cap": "John Anders",
  //           "idx": 0,
  //           "len": 11
  //         },
  //         {
  //           "cap": "John",
  //           "idx": 0,
  //           "len": 4,
  //           "rep": "JOHN"
  //         },
  //         {
  //           "cap": "Anders",
  //           "idx": 5,
  //           "len": 6,
  //           "rep": "Anderson"
  //         }
  //       ]
  //     },
  //     {
  //       "group": [
  //         {
  //           "cap": "Mary Robins",
  //           "idx": 19,
  //           "len": 11
  //         },
  //         {
  //           "cap": "Mary",
  //           "idx": 19,
  //           "len": 4,
  //           "rep": "MARY"
  //         },
  //         {
  //           "cap": "Robins",
  //           "idx": 24,
  //           "len": 6,
  //           "rep": "Robinson"
  //         }
  //       ]
  //     }
  //   ]
  // }

  // Call RegexReplace to update the StringBuilder with the replacements.
  try {
    sb.regexReplace(json);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  print('Result after doing replacements:');
  print(sb.getAsString());

  // Result after doing replacements:
  // JOHN Anderson, +_+_+ MARY Robinson $$$$
}