echo 1970 2014 3000 20000 | perl -ne 'while(/\d{5,}|[3-9]\d{3}/) {$b=$`; $m=$&; $a=$'\''; $m=~s/(?<=\d)(?=(\d\d\d)+\b)/./; $_="$b$m$a"}; print'

1970 2014 3.000 20.000