perldoc -v "$^E"
    $EXTENDED_OS_ERROR
    $^E     Error information specific to the current operating system. At
...
##</code><code>##

$ perldoc perltoc |grep "\^E"
            , $COMPILING, $^C , $DEBUGGING, $^D , ${^ENCODING} , %ENV ,
            ${^CHILD_ERROR_NATIVE} , $EXTENDED_OS_ERROR, $^E ,
        $^E is meaningful on Win32
            $^E, $^H, $^M
        %ENV, CRTL_ENV, CLISYM_[LOCAL], Any other string, $!, $^E, $?, $|