This could be a good addition to File::Spec

sub File::Spec::un_upwards {
    my($self, $foo) = @_;
    $foo = $self->canonpath( $foo );

    my $updir = $self->updir();

    return $foo if -1 == index $foo, $updir;

    my( $volume, $directories, $file ) = $self->splitpath($foo);

    my @dar;
    foreach($self->splitdir( $directories )){
        if( $_ eq $updir ){
            if(@dar){# in case the path is relative, ie ../fo/bar/base
                pop @dar;
            } else {
                push @dar, $_;
            }
        } else {
            push @dar, $_;
        }
    }

    return $self->catpath( 
        $volume,
        $self->catdir( @dar ),
        $file
    );
}
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