substr("0000$1",-4)
sprintf"%04.4d",$1
substr("0"x$maxdigs.$1,-$maxdigs)
sprintf"%0$maxdigs.$maxdigs"."d",$1

##</code><code>##

grep{s/(^|\D)0+(\d)/$1$2/g,1} sort
grep{s/(\d+)/sprintf"%06.6d",$1/ge,1} @sects;