Remove all non digit characters

How can I take a string and remove all non digit characters from the string? Unfortunately my regex skills arent so hot :(

This seems to be working well:

Code:

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        $str = "1234567890abc!@#$&#37;^&*()-=_+[]{}|\\'\"?/><,.";
        echo preg_replace("%[^0-9]%", "", $str);

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Any objections?

No objections. You can use \d as well as 0-9.

how do i turn this into a preg_match?

I need to match if a string is all digits, if so true else false

PHP Code:

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    if(preg_match('/^\d+$/', $str)){
      echo "matched!\n";
    }else{
      echo "no match.\n";
    } 


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