Using Preg Match to check if string contains an underscore

Question

I am trying to check if a string contains an underscore - can anyone explain whats wrong with the following code ``` $str = '12_322'; if (preg_match('/^[1-9]+[_]$/', $str)) { echo 'contains number underscore'; } ```

Accepted Answer

In your regex `[_]$` means the underscore is at the end of the string. That's why it is not matching with yours.

If you want to check only underscore checking anywhere at the string, then:

```
if (preg_match('/_/', $str)) {
```

If you want to check string must be comprised with numbers and underscores, then

```
if (preg_match('/^[1-9_]+$/', $str)) {  // its 1-9 you mentioned
```

But for your sample input `12_322`, this one can be handy too:

```
if (preg_match('/^[1-9]+_[1-9]+$/', $str)) {
```

Using Preg Match to check if string contains an underscore

Solution

Problem