use warnings;
use strict;
use Data::Dumper;

my @lines;
chomp(@lines = <DATA>);
my @sortedlines =   map  { $_->[0] }
                    sort { $a->[1] <=> $b->[1] }
                    map  { [ $_, (split /;/)[0] ] } @lines;
print Dumper(\@sortedlines);

__DATA__
.0000000001;2;1;.5;.2
.5;2;1;.5;.5
0.3;1.5;.5;.5;.2
1;1;.7;1;1
.4;1;.4;1;.5