Pascal (Lazarus/Delphi)

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

Pascal (Lazarus/Delphi)

program ChilkatDemo;

// Demonstrates using the Chilkat Pascal wrapper via the C bridge DLL.
// Builds as a console application under Lazarus (FPC) or Delphi.

{$IFDEF FPC}
  {$MODE DELPHI}
{$ENDIF}
{$APPTYPE CONSOLE}

uses
  {$IFDEF UNIX}
  cthreads,
  {$ENDIF}
  SysUtils,
  CkDllLoader,
  Chilkat.JsonObject,
  Chilkat.StringBuilder;

// ---------------------------------------------------------------------------

procedure RunDemo;
var
  success: Boolean;
  subject: string;
  pattern: string;
  sb: TStringBuilder;
  json: TJsonObject;
  timeoutMs: Integer;
  numMatches: Integer;
  firstNameIdx: Integer;
  lastNameIdx: Integer;
  sbTemp: TStringBuilder;
  i: Integer;

begin
  success := False;

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

  sb := TStringBuilder.Create;
  sb.Append(subject);

  json := TJsonObject.Create;
  json.EmitCompact := False;

  timeoutMs := 2000;
  numMatches := sb.RegexMatch(pattern,json,timeoutMs);
  if (numMatches < 0) then
    begin
      //  Probably an error in the regular expression.
      //  Suggestion: Use AI to help create and/or diagnose regular expressions.
      WriteLn(sb.LastErrorText);
      Exit;
    end;

  //  Examine the matches:
  WriteLn(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 $$$$

  firstNameIdx := json.IntOf('named.first');
  lastNameIdx := json.IntOf('named.last');

  sbTemp := TStringBuilder.Create;

  i := 0;
  numMatches := json.SizeOfArray('match');
  while i < numMatches do
    begin

      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 := i + 1;
    end;

  //  The JSON now has replacement strings:
  WriteLn(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.
  success := sb.RegexReplace(json);
  if (success = False) then
    begin
      WriteLn(sb.LastErrorText);
      Exit;
    end;

  WriteLn('Result after doing replacements:');
  WriteLn(sb.GetAsString());

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


  sb.Free;
  json.Free;
  sbTemp.Free;

end;

// ---------------------------------------------------------------------------

begin

  try
    RunDemo;
  except
    on E: Exception do
      WriteLn('Unhandled exception: ', E.ClassName, ': ', E.Message);
  end;

  WriteLn;
  {$IFDEF MSWINDOWS}
  WriteLn('Press Enter to exit...');
  ReadLn;
  {$ENDIF}
end.