How do I modify the PATH environment variable when running an Inno Setup Installer?

Question

Inno Setup lets you set environment variables via the [Registry] sections (by setting registry key which correspond to environment variable)

However, sometimes you d

Answer 1

The NeedsAddPath in the answer by @mghie doesn't check trailing \ and letter case. Fix it.

function NeedsAddPath(Param: string): boolean;
var
  OrigPath: string;
begin
  if not RegQueryStringValue(
    HKEY_LOCAL_MACHINE,
    'SYSTEM\CurrentControlSet\Control\Session Manager\Environment',
    'Path', OrigPath)
  then begin
    Result := True;
    exit;
  end;
  { look for the path with leading and trailing semicolon }
  { Pos() returns 0 if not found }
  Result :=
    (Pos(';' + UpperCase(Param) + ';', ';' + UpperCase(OrigPath) + ';') = 0) and
    (Pos(';' + UpperCase(Param) + '\;', ';' + UpperCase(OrigPath) + ';') = 0); 
end;