what does perl operator “||=” do?

Question

What does the operator ||= do in perl?

to be more specific if you have a code like:

my ($my_link);
$my_link  ||= DownloadF($file,\'l\') if          


        

Answer 1

If $my_link is false (empty string, 0 or undef) store DownloadF($file,'l') into $my_link

This construct has always had problems when used to assign a default value (what if you want $my_link to be zero)