过滤正则表达式中特定点的输入量？ [关闭]

How would someone do something like this in regex...

^[A-Za-z0-9]{1,254}+@$

[A-Za-z0-9]{1,254} Indicates ,

any character of: 'A' to 'Z', 'a' to 'z', '0' to '9'

(between 1 and 254 times (matching the most amount possible)),

Edit: If you need @ at the end try with the regex [A-Za-z0-9]{1,254}@