Regex Matching numbers with floating point

Question

I have this pattern:

[0-9]*\\.?[0-9]

It matches numbers but it also matches 3.5.4 as:

1. 3.5
2. .4

How to f

Answer 1

To match a json number:

^[-]?(0|[1-9][0-9]*)(\.[0-9]+)?([eE][+-]?[0-9]+)?$

Use this regex to match .123:

^[-]?((0|[1-9][0-9]*)(\.[0-9]+)?|\.[0-9]+)([eE][+-]?[0-9]+)?$

Answer 2

Your regex is not anchored. If you want to match lines that contain only numbers and nothing else use:

^[0-9]*\.?[0-9]$

Answer 3

You have to decide if you want to accept numbers without leading zeros (eg .123). If you don't then the regex is easy:

^-?[0-9]+(\.[0-9]+)?$

If you do then it's a little more complex:

^-?(?:[0-9]+|[0-9]*\.[0-9]+)$

Both presume that a decimal point must be followed by at least one digit. If you don't accept negative numbers then the leading -? is unnecessary.

Answer 4

You should not use a regex for this unless you really need to.

Instead, you should use your language's built-in number parsing methods.

I assume from your other questions that you're using Javascript; if so, you should call parseFloat.

Answer 5

Updated answer after comment from poster:

Use lookahead / lookbehind to make sure that the characters before and after are spaces:

Here's a version that closely matches yours, but that won't make partial matches:

(?:^|(?<=\s))[0-9]*\.?[0-9](?=\s|$)

For both these examples, when run on the string 1 2.3.4 5.6 it matches only 1 and 5.6.