如何截取字符串里的字符?

我现在有一个字符串"123,4567,78902",如何把里面的数字分别取出来放到3个变量里,
谢谢!
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"; } ?> \--------------------------------------------------------------- $str = "123,4567,78902"; $aa = explode(',', $str); print " ```

";   
print_r($aa);   
print "

``` ";