((?:\[.*?\]){1,4})

##</code><code>##

my @indexes;
my $re = qr{
    ...           # everything before
    (?:
     \[           # opening [
     ([^\]]+)     # everthing except ]
     \]           # closing ]
     (?{ push @indexes, $^R}) # store the match
    )+            # as many times as you want
}x

##</code><code>##

re:  (..) (..)+
vars: $1   $2