Ooops. Just needs a little positive lookbehind. 

perl -le 'for(@ARGV){s/\./,/;s/(?<=\d)(?=(\d\d\d)+(,|\Z))/./g;print}' 
+1234567.89 234567.89 1234567 234567
1.234.567,89
234.567,89
1.234.567
234.567

[download]

update..

Ok.. yours is shorter... mine is probably more efficient for not invoking $& at least :)

                - Ant
                - Some of my best work - (1 2 3)

In reply to Re^2: Golf, anyone? :) by suaveant
in thread disappearing digit with regex and tr by zentara

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