C＃正则表达式明确匹配字符串

Question

I want to match only words from AZ and az with an optional period at the end. This is the code I have so far:

return Regex.IsMatch(word, @"[A-Za-z]\.?")

This means the following should return true: test , test. .

The following should return false: t3st , test.. , . , .

Right now this regex returns true for everything.

Answer 1

Try this regex :

@"^[A-Za-z]+\.?$"

Boundary matchers

• ^ means beginning of a line
• $ means end of a line

Greedy quantifier

• [A-Za-z]+ means [A-Za-z], one or more times

Answer 2

Your regex only asks for a single letter followed by an optional period. Since all your words start with a letter, that regex returns true.

Notice the + in Prince John Wesley's answer - that says to use one or more letters, so it'll "eat" all the letters in the word, stopping at a non-letter. Then the \\.? tests for an optional period.

I don't think the ^ and $ are needed in this case.

You might also want to include the hyphen and the single-quote in your regex; otherwise you'll have problems with hyphenated words and contractions.

That may get messy; some words have more than one hyphen: "port-of-call" or "coat-of-arms", for example. Very rarely you'll find a word with more than one quote: "I'd've" for "I would have". They're rare enough you can probably forget about 'em. (oops! there's a word that starts with a quote... :)