/(\d\s+foo)[^\r\n]*(\d\s+foo)/

##</code><code>##

my $re = qr/\d\s+foo/;
sub match {
  local $_ = shift;
  /(\d\s+foo)[^\r\n]*\1/x       and print "1\n";
  /\d\s+foo  [^\r\n]*\d\s+foo/x and print "2\n";
  /($re)     [^\r\n]*\1/x       and print "3\n";
  /$re       [^\r\n]*$re/x      and print "4\n";
}
match '4  foo4  foo';   ## easily matched
match '4  foo5  foo';   ## a bit trickier

__OUTPUT__

1
2
3
4
2
4