正则表达式允许空字符串或具有特定长度的字符串(Regular Expression to allow an empty string or a string with specific length)

正则表达式允许空字符串或具有特定长度的字符串(Regular Expression to allow an empty string or a string with specific length)

嗨，我无法尝试创建一个正则表达式，允许我将字段设置为空，或者填充长度为9的字符串。

目前使用的正则表达式是： ^[0-9]{9}

如果该字段是必填字段，则该字段有效，但是我们有一个新要求，即它也可以为空。 我已经尝试了^[0-9]{0|9 }，但显然不起作用。

提前致谢

Hi I am having trouble trying to create a regex that will allow me to have the field empty or a string with length 9 if populated.

The current regex im using is: ^[0-9]{9}

Which works if the field is mandatory, however we have a new requirement that this can also be empty. I've tried ^[0-9]{0|9} but obviously that doesnt work.

Thanks in advance

最满意答案

^(|[0-9]{9})$

应该做的伎俩。

编辑：但认真; 做@Felix Kling在评论中建议：通过.length属性， .equals("")等测试字符串。

^(|[0-9]{9})$

Should do the trick.

Edit: But seriously; do what @Felix Kling suggests in a comment: test the string via a .length property, .equals("") or the like.