一个只允许字母、数字、破折号和点的验证正则表达式看起来如何，强制至少一个点而不是第一个字符？

Question

I am really bad at Regex but in my JavaScript app I am trying to validate a form item, the value of the form item can only contain letters, numbers, dashes and at least one dot.

So the following would be valid:

hello.world

microsoft.com

So far I came up with this (.+)[a-zA-Z0-9.-]\.[a-zA-Z0-9.-]+$ but it doesn't work as I can add spaces. What can I do to make my Regex work? Also can I prevent the dot being the first character?

Answer 1

I think you can achieve this with the following

^[^.][a-zA-Z0-9.-]+$

^[^.] is no starting dots

[a-zA-Z0-9.-] is all characters lowercase, uppercase and digits including dot and hyphens. Credit to Wiktor & Peter for leading me to this

$ makes sure it's the end of the string, so it won't match on a partial like "hello world"

Example here: https://regex101.com/r/BXHmwh/1

Answer 2

The so far accepted answer does not fully meet the OP's requirements which are...

the value of the form item can only contain letters , numbers , dashes and at least one dot . ... Also... prevent the dot being the first character ...

NJDawson 's regex... ^[^.][a-zA-Z0-9.-]+$ ... does fail at the last requirement because it allows as first character any character which is not a dot where the OP requires any of the above quoted characters except the dot.

Example:

 const regX = (/^[^.][a-zA-Z0-9.-]+$/); console.log( "regX.test('.foo-bar.baz-9')?", // false as expected regX.test('.foo-bar.baz-9') // because of dot first. ); console.log( "regX.test('#foo-bar.baz-9')?", // true which violates regX.test('#foo-bar.baz-9') // the requirements ); // due to using #.

One can fully meet the requirements by updating the regex to something more expressive like... ^[a-zA-Z0-9-]+\.[a-zA-Z0-9.-]*$ ... which makes sure that neither a dot nor any other character than one of the allowed ones sits at the first position of the to be tested string and also forces the string to contain at least one dot in addition to the other allowed characters.

Updated example:

 const regX = (/^[a-zA-Z0-9-]+\.[a-zA-Z0-9.-]*$/); console.log( "regX.test('.foo-bar.baz-9')?", // false as expected regX.test('.foo-bar.baz-9') // because of dot first. ); console.log( "regX.test('#foo-bar.baz-9')?", // false as expected regX.test('#foo-bar.baz-9') // because of hash first. ); console.log( "regX.test('+foo-bar.baz-9')?", // false as expected regX.test('+foo-bar.baz-9') // because of plus first. ); console.log( "regX.test('-foo-bar.baz-9')?", // true as expected. regX.test('-foo-bar.baz-9') ); console.log( "regX.test('9.-foo-bar.baz')?", // true as expected. regX.test('9.-foo-bar.baz') ); console.log( "regX.test('9a-foo-bar-baz')?", // false as expected. regX.test('9a-foo-bar-baz') // bacause of missing dot. );