Thank you very much! Now it works with the following code: 
use strict;
use warnings;
while(<DATA>)    {    
    chomp;
    $_=~s/(\d{5} \w+)/ \1\n/g;
    print;
}

__DATA__
Some Company; Some Street 52
12345 City1
Another Company; Another Street 63
23456 City2
Yet Another Company; New Street 11
34546 City3

[download]
Is this a reasonable code or I just have luck now?
Many thanks!
VE

In reply to Re: Regex with Newline by Anonymous Monk
in thread Regex with Newline by Anonymous Monk

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