Question

what the regular expression of a line of string containing ONLY float numbers separated with spaces or tabs. The float number can be negative, like -999.999

Answer 1

Let’s come up with a regex for a float, and then see what we can do about the rest.

A float is:

• An optional negative sign
• Followed by a number of digits
• Followed by an optional decimal point and then more digits
• Followed be “e”
• Followed by a number of digits (with an optional sign).

Put that together, and we get:

/-?[0-9]+(\.[0-9]+)?([Ee][+-]?[0-9]+)?/

Now, this is pretty loose, but you can tweak it if you want to tighten it up a little. Now, for any number of these with spaces in between, it’s pretty trivial:

/^(F\s+)+$/

Put it all together, we end up with:

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