Regular Expression Extract Substring using Start and End Pattern

Question

for exemple i have a QT RCC File contain list of png Files
where every PNG has by default:
the Start Pattern:
++++++++++++++++++++++++++++++++++++++
PNG HEADER = (89 50 4E 47 0D 0A 1A 0A)
in Decoded Text is: ‰PNG....
======================================
the End Pattern:
++++++++++++++++++++++++++++++++++++++
PNG FOOTER = (49 45 4E 44 AE 42 60 82)
in Decoded Text is: IEND®B‚`
======================================
my question is:
I would like to save each Succeded Match Range as a ".png" file, like I do with the HEX Editor Manually.
i load the file into a SynEdt as Hex DATA using this code:

const
  PngHeader = '89504E470D0A1A0A';
  PngFooter = '49454E44AE426082';

implementation

uses
  System.IOUtils,
  System.RegularExpressions,
  Vcl.Imaging.pngimage,
  System.Generics.Collections;
  
procedure FileViewHex(AMemo: TSynEdit; FileName: string);// use SynEdit instead of TMemo
const
  MaxLineLength = 16 * 2; // each byte displayed with 2 characters (if you want add a space then replace "2" by "3"
  BufferSize = 4096;
var
  DataFile: File;
  Buffer: array[1..BufferSize] of byte;
  BytesRead, I: integer;
  HexByte, Line: string;
begin
  AssignFile(DataFile, FileName);
  Reset(DataFile, 1);
  AMemo.Clear;
  while not Eof(DataFile) do begin
    BlockRead(DataFile, Buffer, BufferSize, BytesRead);
    Line := '';
    for I := 1 to BytesRead do begin
      HexByte := IntToHex(Buffer[I], 1); // convert a byte to hexadecimal
      // Add leading 0 if result is shorter than 2, easier to read...
      if Length(HexByte) < 2 then HexByte := '0' + HexByte;
      Line := Line + HexByte;// + ' '; // the space
      if Length(Line) >= MaxLineLength then begin
        AMemo.Lines.Add(Line);
        Line := '';
      end;
    end;
  end;
  // If not already added, add last line to TMemo
  if Length(Line) > 0 then AMemo.Lines.Add(Line);
  CloseFile(DataFile);
end;  

procedure Get_PngList(Stream: string; PngList: TListView);
var
  Matches: TMatchCollection;
  Match: TMatch;
  I: Integer;
  Item: TListItem;
begin
  I := 0;
  Matches := TRegEx.Matches(Stream, PngHeader+'.*?'+PngFooter, [roIgnoreCase, roMultiLine]);
  for Match in Matches do
  begin
    if Match.Success then
    begin
      Item := PngList.Items.Add;
      Item.Caption := I.ToString;
      Item.SubItems.Add(Match.Value);
     Inc(I);
    end;
  end;
end;

i need to know the correct Pattern..

That approach is flawed: when your PngFooter is split over two lines you'll never find it. On top using Regex on hexadecimal Strings is very pointless - you could do the same just directly with bytes. And the PNG footer might also appear inbetween the file, not only at the end of it. — AmigoJack
– AmigoJack, Commented Jul 22, 2021 at 8:24
@AmigoJack According to what I understood from what you said, A PNG image can have more than one footer ('49454E44AE426082'), And this is impossible in my opinion — Roberto
– Roberto, Commented Jul 22, 2021 at 11:42
He meant image data can accidentally contain sequences that are identical to a footer (although the chances of this happening are quite low). — Olivier
– Olivier, Commented Jul 22, 2021 at 11:58
@Olivier yes that exactly what i understand too, but this phenomenon is impossible in my opinion otherwise that png where contain inside her HEX Data a sequences that are identical to a footer (this mean can't be opened with any image viewer) — Roberto
– Roberto, Commented Jul 22, 2021 at 12:09
An image viewer could perfectly open such a PNG. Viewers perform a real parsing. They don't use a regex like you're trying to do. — Olivier
– Olivier, Commented Jul 22, 2021 at 12:13

Ryszard Czech · Accepted Answer · 2021-07-25 20:05:37Z

Use \s? between each character to allow matches that are "broken" by line feed characters:

8\s?9\s?5\s?0\s?4\s?E\s?4\s?7\s?0\s?D\s?0\s?A\s?1\s?A\s?0\s?A([\s\S]*?)4\s?9\s?4\s?5\s?4\s?E\s?4\s?4\s?A\s?E\s?4\s?2\s?6\s?0\s?8\s?2

See regex proof.

EXPLANATION

--------------------------------------------------------------------------------
  8                        '8'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  9                        '9'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  5                        '5'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  0                        '0'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  4                        '4'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  E                        'E'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  4                        '4'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  7                        '7'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  0                        '0'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  D                        'D'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  0                        '0'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  A                        'A'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  1                        '1'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  A                        'A'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  0                        '0'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  A                        'A'
--------------------------------------------------------------------------------
  (                        group and capture to \1:
--------------------------------------------------------------------------------
    [\s\S]*?                 any character of: whitespace (\n, \r,
                             \t, \f, and " "), non-whitespace (all
                             but \n, \r, \t, \f, and " ") (0 or more
                             times (matching the least amount
                             possible))
--------------------------------------------------------------------------------
  )                        end of \1
--------------------------------------------------------------------------------
  4                        '4'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  9                        '9'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  4                        '4'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  5                        '5'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  4                        '4'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  E                        'E'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  4                        '4'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  4                        '4'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  A                        'A'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  E                        'E'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  4                        '4'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  2                        '2'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  6                        '6'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  0                        '0'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  8                        '8'
--------------------------------------------------------------------------------
  \s?                      whitespace (\n, \r, \t, \f, and " ")
                           (optional (matching the most amount
                           possible))
--------------------------------------------------------------------------------
  2                        '2'

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