As you might know; in Lazarus you can add version and build info to the executable (at least under Linux, Windows, and MacOS X).
The question is - for example for an About box - how do I extract that information from my executable at runtime? And ... preferably cross platform.

Follow these steps:

1. Add units vinfo (step 3 creates the unit) and versiontypes to the Uses clause.

2. Add code to one of the forms (typically the main form so you can read it if you make it a property of tform).

As you can see in the code below, version info can be extracted from the TVersionInfo object:

  ...
var    Info: TVersionInfo;
         Version: string;
begin
  // Get application compiled version#
  Info := TVersionInfo.Create;
  Info.Load(HINSTANCE);
  Version := Format('%d.%d.%d', [Info.FixedInfo.FileVersion[0],Info.FixedInfo.FileVersion[1],Info.FixedInfo.FileVersion[2]]);
  Info.Free;
  self.Caption:='Name My TV Series v'+Version+' - © Hans Luijten - www.tweaking4all.com';   
  ...

3. Create and save the file vinfo.pas (which we added to the sues clause in step 1).

unit vinfo;
{$mode objfpc}
interface
uses
  Classes, SysUtils, resource, versiontypes, versionresource;
type
  { TVersionInfo }
  TVersionInfo = class
  private
    FVersResource: TVersionResource;
    function GetFixedInfo: TVersionFixedInfo;
    function GetStringFileInfo: TVersionStringFileInfo;
    function GetVarFileInfo: TVersionVarFileInfo;
    function SearchValue(const aString : string) : string;
  public
    constructor Create;
    destructor Destroy; override;
    function CompanyName  : string;
    function InternalName : string;
    function FileVersion  : string;
    function ProductName  : string;
    procedure Load(Instance: THandle);
    property FixedInfo: TVersionFixedInfo read GetFixedInfo;
    property StringFileInfo: TVersionStringFileInfo read GetStringFileInfo;
    property VarFileInfo: TVersionVarFileInfo read GetVarFileInfo;
  end;
implementation
{ TVersionInfo }
function TVersionInfo.GetFixedInfo: TVersionFixedInfo;
begin
  Result := FVersResource.FixedInfo;
end;
function TVersionInfo.GetStringFileInfo: TVersionStringFileInfo;
begin
  Result := FVersResource.StringFileInfo;
end;
function TVersionInfo.GetVarFileInfo: TVersionVarFileInfo;
begin
  Result := FVersResource.VarFileInfo;
end;
function TVersionInfo.SearchValue(const aString: string): string;
var s : TVersionStringTable;
    i,j : integer;
begin
  result := '';
  for i:=0 to StringFileInfo.Count-1 do begin
      s := StringFileInfo.Items;
      for j:=0 to s.Count-1 do
          if s.Keys[j] = aString then begin
             result := s.Values[j];
             break;
          end;
  end;
end;
function TVersionInfo.CompanyName: string;
begin
   Result := SearchValue('CompanyName');
end;
function TVersionInfo.InternalName: string;
begin
   Result := SearchValue('InternalName');
end;
function TVersionInfo.FileVersion: string;
begin
   Result := SearchValue('FileVersion');
end;
function TVersionInfo.ProductName: string;
begin
   Result := SearchValue('ProductName');
end;
constructor TVersionInfo.Create;
begin
  inherited Create;
  FVersResource := TVersionResource.Create;
  Load(HInstance);
end;
destructor TVersionInfo.Destroy;
begin
  FVersResource.Free;
  inherited Destroy;
end;
procedure TVersionInfo.Load(Instance: THandle);
var
  Stream: TResourceStream;
begin
  Stream := TResourceStream.CreateFromID(Instance, 1, PChar(RT_VERSION));
  try
    FVersResource.SetCustomRawDataStream(Stream);
    // access some property to load from the stream
    FVersResource.FixedInfo;
    // clear the stream
    FVersResource.SetCustomRawDataStream(nil);
  finally
    Stream.Free;
  end;
end;
end.