I forgot about the special behaviour of .. in scalar context, when the operands are literal integers. In that case, that value is automatically compared against $.. So my code can be simplified to:

open IN, "<", $file or die "Can't open file $file: $!";
my %data;
while(<IN>) {
    if(1 .. 2) {
        my($number) = /([\d.]+)\s*$/;
        $data{$.} = $number;
    }
}
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If you need several distinct ranges, you can do

if(1 .. 2 or 6 .. 8) {
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as can be demonstrated using the following code:

while(<DATA>) {
    if(1 .. 2 or 6 .. 8) {
        print "$.: $_";
    }
}
__DATA__
one
two
three
four
five
six
seven
eight
nine
ten
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Result:

1: one
2: two
6: six
7: seven
8: eight

For a single value, you can choose between 4 == $. and 4 .. 4:

if(1 .. 2 or 4 == $. or 6 .. 8) {
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if(1 .. 2 or 4 .. 4 or 6 .. 8) {
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