正则表达式用于特定数字或特定单词

Question

For a security question on a form, I want the user to enter either 4 or four , or any variation of the latter.

Right now I have this regex /\\b4|four\\b/gi that is a variation of one I've found on this site. The problem is that the user can enter 458 or something. So, can somebody help me out?

Answer 1

I'm not sure what you mean by "any variation of the latter", but:

/^(4|four)$/i

will match the entire string being either 4 or four. The ^ matches only at the start and $ only at the end. /i means case insensitive (so FOUR would be accepted as well). Some languages don't take flags like that (in them, you'll have to check the docs on how to do an insensitive match). If you can't use a case-insensitive match, you can do this instead:

/^(4|[fF][oO][uU][rR])$/i

Of course, whatever language you're working in probably also has equality comparisons. So you could just do (for example)

if (str == "4" || str == "four")

Answer 2

Try:

^4|four$

which will match "4" and "four". Depending on the programming language that you use there might be a case insensitive option like C#'s RegexOptions.IngoreCase

Answer 3

So you should be using a case-insensitve comparison for this. Some (perhaps most) regex flavors will support the pattern (?i) to denote case insensitivity.

^(?i)(?:4|four)$

But if this is JavaScript then you can use a syntax more like what you started with...

/^(?:4|four)$/i

The /i is for case insensitivity in this case. But I removed /g since it's for global matching and wouldn't be needed here.

Notice that I also put 4|four inside a (?:non capturing) group. This is more efficient than using a traditional (capturing) group when you don't need to do anything with the captured value.

Then the ^ and $ anchors surrounding everything will ensure you have no extra leading or following characters.