This passes all your test cases: 
use strict;
use warnings;
use Test::Simple qw(no_plan);
my %test_cases = (
    '   999' => 'valid',
    '  9999' => 'valid',
    '999999' => 'valid',
    '     9' => 'valid',
    ' 99 9'  => 'invalid',
);

foreach my $case (keys %test_cases) {
    my $does_match
        = $case =~ /
            ^\s*        # any number of leading spaces
            \d+         # followed by a number of digits
            (:?
            [^\s]*      # but cant have any spaces after a digit has b
+een found
            \d+         # It must contain at least one digit at the en
+d
            )?$
        /x ;
    ok( !($does_match xor $test_cases{$case} eq 'valid'),
        "'$case': $test_cases{$case}" );
}

[download]
OUTPUT: 
ok 1 - '999999': valid
ok 2 - '   999': valid
ok 3 - '     9': valid
ok 4 - '  9999': valid
ok 5 - ' 99 9': invalid
1..5

[download]
Bill

In reply to Re: Should be a simple spaces/digits regex....but I'm turning grey! by BillKSmith
in thread Should be a simple spaces/digits regex....but I'm turning grey! by viffer

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.