Decimal or numeric values in regular expression validation

> # this regex was suggested by Nikita in http://stackoverflow.com/a/31169781/1613005
> a <- c("m", "2..3", "2-", "2...3", "2.4.3", "5-6-7", "2", "2.5", ".2", ".2")
> grep(pattern="(-?0[.]\\d+)|(-?[1-9]+\\d*([.]\\d+)?)|0$", a, perl=T)
[1]  2  3  4  5  6  7  8  9 10
>