Not bad, especially given the simplicity. More potential false negatives to go with jdporter's. 

for my $input (qw<
    +4
    1.0
    1e5
    12345678901234567890
    1.234567890123456789
>) {
    if( $input+0 eq $input ) {
        print "$input is a number!\n";
    } else {
        print "$input is not ", 0+$input, "\n";
    }
}
__END__
+4 is not 4
1.0 is not 1
1e5 is not 100000
12345678901234567890 is not 1.23456789012346e+019
1.234567890123456789 is not 1.23456789012346

[download]

Update: It successfully detects if $input is (primarily) holding a numeric value (an IV or NV, how Perl stores an integer and floating point, respectively) or is holding a string value that equals the canonical string representation of any possible Perl numeric value.

So I don't believe that there are any false positives. The false negatives are the many ways to reasonably represent a numeric value that aren't Perl's canonical representation.

- tye        

In reply to Re^4: How to check Inputs if Numeric (eq 0+) by tye
in thread How to check Inputs if Numeric by kasmot

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.