Given the format that you have, setting $/ (the input record separator) is an easy way to do this: 
use strict;
use warnings;

local $/="rooms\n";
while(<DATA>) {
        print;
}
__DATA__
1000001 01.11.199600.00.00001 A1 1 SN Y
2001.11.200400098.0500073.5500083.35
5001.11.1997Professional attendance being an attendance at
5001.11.1997other than consulting rooms
1000002 01.11.199600.00.00001 A1 1 SN Y
2001.11.200400098.0500073.5500083.35
5001.11.1997Professional attendance being an attendance at
5001.11.1997consulting rooms

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thor

Feel the white light, the light within
Be your own disciple, fan the sparks of will
For all of us waiting, your kingdom will come

In reply to Re: Format multiline to single line records by thor
in thread Format multiline to single line records by kerrya

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