如何用正则表达式提取收据中的最后价格？

Hey there! Let's figure out why your current regex isn't working and fix it.

Why Your Current Regex Fails #

Your regex (?!\d+\s+TOTAL\s+)\$+\d+\.?\d+\s+(?=.*\$\d+\.?\d+) uses a positive lookahead (?=.*\$\d+\.?\d+) which tells the engine "only match this dollar amount if there's another dollar amount somewhere after it". That's exactly why it's picking $23.00 and $0.03—both have another dollar amount following them. The last amount $23.80 doesn't have any after it, so it gets excluded.

The Fix: Match the Last Dollar Amount #

We need to reverse that logic: match a dollar amount only if there are no more dollar signs after it until the end of the string. Here's the regex to do that:

\$\d+(?:\.\d+)?(?!.*\$)

Let's break down what each part does:

• \$: Matches the dollar sign (escaped because it's a special character in regex).
• \d+: Matches one or more digits (the whole number part).
• (?:\.\d+)?: An optional non-capturing group for the decimal part—\. matches the dot, \d+ matches one or more decimal digits, and ? makes this whole group optional (so it works for amounts like $5 or $5.00).
• (?!.*\$): Negative lookahead that ensures there are no more dollar signs (\$) anywhere after the matched amount (.* matches any characters in between).

Testing with Your Input #

For your input string " $23.00$0.03$23.80 ", this regex will only match $23.80 because it's the only dollar amount with no subsequent $ signs.

Alternative Approach: Capture the Last Amount with Greedy Matching #

If you prefer using group capture, you can use this regex to greedily match everything up to the last dollar amount, then capture that final amount:

.*(\$\d+(?:\.\d+)?)

In this case, the actual amount will be in capture group 1 (you'll need to extract that group instead of the full match). This works because .* greedily consumes all characters until the last occurrence of the dollar amount pattern.

Hope this solves your problem!

内容的提问来源于stack exchange，提问作者Davie Overman