PHP的简单PCRE正则表达式只允许一个点或没有？

Question

I'm trying to create a regex for alias validation:

And I'm allowing letters, numbers and 1 dot.

I have done the following:

/^[a-z0-9\\.]+$/i

However it allows more then 1 dot?

Answer 1

This should do it:

/^(?:\.[a-z0-9]+|[a-z0-9]+(?:\.[a-z0-9]*)?)$/i

This allows the string to either:

• start with one dot that is followed by at least one alphanumeric character, or
• start with one or more alphanumeric character that may be followed by one dot and zero or more alphanumeric characters.

Answer 2

try this:

^(?:[a-z0-9]+\.?[a-z0-9]*|[a-z0-9]*\.?[a-z0-9]+)$

places the dot in the center, then allows it to be surrounded on either side.

Answer 3

我认为在这种情况下，允许将点作为第一个或最后一个字符不是一个好主意：

/^[a-z0-9]+\.?[a-z0-9]+$/i