Task for matching floating point numbers

Question

Task:

MATCH:
3.45
5,4
.45
3e4
,54
4
4.
4,

DON'T MATCH:
4,5e
2e
.3.
2e,4
,4.
d34
2.45t
2,45.

Currently i came up with the following:

(?<=\s|^)[-+]?(?:(?:[.,]?\d+[.,]?\d*[eE]\d+(?!\w|[.,]))|[.,]?\d+[.,]?\d*(?!\w|[.,]))\b

That works for almost everything, except 2 last numbers (4. and 4,) and got stucked

Answer 1

You may use

(?<!\S)[-+]?[0-9]*(?:[.,]?[0-9]+(?:[eE][-+]?[0-9]+)?|(?<=\d)[,.])(?!\S)

See the regex demo

Details

• (?<!\S) - start of string or a whitespace must appear immediately to the left
• [-+]? - an optional + or -
• [0-9]* - 0+ digits
• (?:[.,]?[0-9]+(?:[eE][-+]?[0-9]+)?|[,.]) - either
  • [.,]?[0-9]+(?:[eE][-+]?[0-9]+)? - an optional . or ,, then 1+ digits, then an optional sequence of e or E, followed with an optional . or , and 1+ digits
  • | - or
  • (?<=\d)[,.] - a dot or comma only if preceded with a digit (to avoid matching standalone . or ,)
• (?!\S) - end of string or a whitespace must appear immediately to the right.

Regex graph: