There were answers provided but I was missing the all critical, 'why does it happen this way?' One quick test shows that it probably should not:

 perl -e '$_ = 100; for(1..5){};print;'

[download]
Produces '100', not '5'. Obviously for localizes $_, but apparently while does not...

From Programming Perl Section 4.4.1: Unlike the foreach loop we'll see in a moment, a while loop never implicitly localizes any variables in its test condition. This can have "interesting" consequences when while loops use globals for loop variables.

So you don't really need to add new variables at all. You need to force Perl to localize $_, like so: 

#...
    open FLOORFILE, $floorfile or die $!;
    {
          local($_);
          while (<FLOORFILE>)
          {
               print "$_\n";
          }
    }
    
#...

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Now the output is this: 
...
building2

floor1
aldfja;jd;af

floor2
aldfja;jd;af

floor3
aldfja;jd;af

[download]

Celebrate Intellectual Diversity

In reply to Re: Problem with while loop inside a foreach loop by InfiniteSilence
in thread Problem with while loop inside a foreach loop by andylevel2

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