perl -E '
    use Scalar::Util "looks_like_number";

    for (qw{Inf -Inf Infinity -Infinity}) {
        say "$_: ", looks_like_number($_) ? 1 : 0;
    }
'
Inf: 1
-Inf: 1
Infinity: 1
-Infinity: 1

##</code><code>##

perl -E '
    use Scalar::Util "looks_like_number";

    for (qw{1 0b10 0o10 0x10}) {
        say "$_: ", looks_like_number($_) ? 1 : 0
    }
'
1: 1
0b10: 0
0o10: 0
0x10: 0

##</code><code>##

perl -E '
    use Scalar::Util "looks_like_number";

    for (1, 0b10, 0o10, 0x10) {
        say "$_: ", looks_like_number($_) ? 1 : 0
    }
'
1: 1
2: 1
8: 1
16: 1

##</code><code>##

sub IsNumber {
    state $re = qr{...};
    return $_[0] =~ $re;
}

##</code><code>##

{
    my $re; BEGIN { $re = qr{...} }

    sub IsNumber {
        return $_[0] =~ $re;
    }
}

##</code><code>##

$ perl -E 'say 1e6'
1000000

##</code><code>##

$ perl -E 'say 1_000_000/1_000'
1000