Useful regex's to verify email, alphanumeric, numeric (to ensure that an entire string matches)

Regex is a black art, with the usual rule being the smaller the better.

The following are a basic collection that I use quite often:

Regex to validate email - i.e. of the form x@a.tld

^[a-zA-Z0-9_\.\-]+@[a-zA-Z0-9\-]+\.[a-zA-Z0-9\.\-]+$

Regex to match only alphanumeric
```
^([a-zA-Z0-9]+)$
```
Regex to match only alpha
```
^([a-zA-Z]+)$
```
Regex to match only numeric
```
^([0-9]+)$
```
Regex to match only numeric (decimal or floating point)
```
^([0-9.]+)$
```
Regex to match only numeric (international)
```
^([0-9.,]+)$
```