Regular expression to match German number

Question

I am wondering, how would regular expression for testing correct format of number for German culture would look like.

In German, comma is used as decimal mark and do

Answer 1

This is the regex I would use:

^-?\d{1,3}(?:\.\d{3})*(?:,\d+)?$

Debuggex Demo

And this is a code example to interpret it as a valid floating point (notice the parseFloat() after the string replacements).

Edit: as mentioned in Severin Klug's answer, the below code assumes that the numbers are known to be in German format. Attempting to "detect" whether a string contains a German format or US format number is not arbitrary and out of scope for this question. '1.234' is valid in both formats but with different actual values, without context it is impossible to know for sure which format was meant.

var numbers = ['1.000', '1,000', '1.000,89', '1.000.123.456,89'];

document.getElementById('out').value=numbers.map(function(str) {
  return parseFloat(str.replace(/\./g, '').replace(',', '.'));
}).join('\n');