source: bootcd/isolinux/syslinux-6.03/gnu-efi/gnu-efi-3.0/apps/printenv.c

#include <efi.h>
#include <efilib.h>

EFI_STATUS
efi_main (EFI_HANDLE image, EFI_SYSTEM_TABLE *systab)
{
        EFI_STATUS status;
        CHAR16 name[256], *val, fmt[20];
        EFI_GUID vendor;
        UINTN size;

        InitializeLib(image, systab);

        name[0] = 0;
        vendor = NullGuid;

        Print(L"GUID                                Variable Name        Value\n");
        Print(L"=================================== ==================== ========\n");

        StrCpy(fmt, L"%.-35g %.-20s %s\n");
        while (1) {
                size = sizeof(name);
                status = uefi_call_wrapper(RT->GetNextVariableName, 3, &size, name, &vendor);
                if (status != EFI_SUCCESS)
                        break;

                val = LibGetVariable(name, &vendor);
                Print(fmt, &vendor, name, val);
                FreePool(val);
        }
        return EFI_SUCCESS;
}