正则表达式匹配字符串末尾的数字

Question

I'm trying to match a number at the end of a string, using a regex. For example, the string might look like:

var foo = '101*99+123.12'; // would match 123.12
var bar = '101*99+-123';   // would match -123
var str = '101*99+-123.';  // would match -123.

This is what I've got so far, but it seem to match the entire string if there is no decimal point:

foo.match(/\-?\d+.?\d+?$/);

I take this to mean:

• \\-? : optional "-" symbol
• \\d+ : 1 or more digits
• .? : optional decimal point
• \\d+? : optional 1 or more digits after decimal point
• $ : match at the end of the string

What am I missing?

Answer 1

. matches any character. You need to escape it as \\.

Try this:

/-?\d+\.?\d*$/

That is:

-?           // optional minus sign
\d+          // one or more digits
\.?          // optional .
\d*          // zero or more digits

As you can see at MDN's regex page , +? is a non-greedy match of 1 or more, not an optional match of 1 or more.

Answer 2

Several issues:

• side note : the dash doesn't need to be escaped; it's only special in character classes (eg [az] ).
• the dot is special; it means "match any character". You'll want to escape it: \\.
• \\d+? actually means: match at least one digit, but if the regex goes on after that part of the pattern, try to match the remaining regex as early as possible (" lazy " or "non-greedy matching"). In your case this ? just does nothing. To make those digits truly optional, use \\d* .
• Finally, you might want to make the decimal point and the subsequent digits optional as a group: (\\.\\d+)?

Executive summary: /-?\\d+(\\.\\d+)?$/

Answer 3

This should do the job /-?\\d+\\.?\\d*$/

result = subject.match(/-?\d+\.?\d*$/mg);

Answer 4

If the pattern is always x*y+z then you could do this alternatively without a regex like so.

var foo = '101*99+123.12'; // would match 123.12
var bar = '101*99+-123';   // would match -123
var str = '101*99+-123.';  // would match -123.

function getLastNumber(string) {
    return string.split("+")[1];
}

console.log(getLastNumber(foo));
console.log(getLastNumber(bar));
console.log(getLastNumber(str));

Output

123.12
-123
-123.

On jsfiddle