grep pattern to exclude negative numbers from file

Question

I have been struggling trying to come up with an easier answer to this problem. But still using grep.

I want to grep out the positive (and negative numbers) of myfile.dat. Myfile.dat look like this:

-1.4987 4.1354  -8.1235
4.2322  -0.9842 -2.6845
3.6845  1.5132  -2.8452
0.0122  9.3542  -1.2354
-7.2127 -1.1253 -4.3967
0.3535  7.2416  -3.1277

No need to retain column format. So I have used the following grep patterns.

Negative numbers:

grep -E -o [-][0-9]+.[0-9]+ myfile.dat

Positive numbers (here I have to pipe all numbers into another grep):

grep -Eo [-]\?[0-9]+.[0-9]+ myfile.dat | grep -v [-]

Here comes the question! Is there a grep pattern that allows me to extract positive numbers directly, without the use of a second grep command?

This is all about the pattern, not whether I could use another command.

Answer 1

Using grep -P you can do this to get all positive numbers:

 grep -oP '(?<!-)\b[0-9]+\.[0-9]+\b' file

Answer 2

You could match on beginning-of-line or space before digits:

$ grep -oE '(^| )[0-9]+\.[0-9]+' Myfile.dat | tr -d ' '
4.1354
4.2322
3.6845
1.5132
0.0122
9.3542
0.3535
7.2416

tr -d ' ' just removes any initial spaces from the output, you can skip it if not needed.