bash - How do you escape a hyphen as character range in a POSIX regex

Question

I have a csv file full of values such as this:

0.00145423,3.03795e-05

I wanted to check that all the lines were consistent so I tried to grep for any unexpected characters like so...

grep '[^0-9,e-.]' myfile

In my mind it goes like this: find a line with any character [] that is not ^ a number 0-9, comma ,, letter e e, hyphen - (attempted to escape with ), or a period .. However, hyphens still continue match.

[EDIT]This does not happen in python, only with bash/grep:

>>> re.search("[^0-9,e-.]", "0.00145423,3.03795e-05")
>>> 

unsatisfying solution:
If I move the escaped hyphen to the end it works:

grep '[^0-9,e.-]' myfile

Putting the escaped hyphen next to the 0-9 range results in grep: Invalid range end.

Can someone explain what's going on? Is this some bash argument parsing issue or something specific to grep?

bash4.3.33, grep2.21

Answer 1

The way to include a literal - in a character list is to put it in the first or last position of the bracket expression, exactly as shown in the answer at: Get final special character with a regular expression.

From POSIX 9.3.5 RE Bracket Expression: The <hyphen> character shall be treated as itself if it occurs first (after an initial '^', if any) or last in the list, or as an ending range point in a range expression.

Some tools might have additional ways of doing it with some kind of escaping but you're always safe to just put it first or last. Note that - isn't the only character that has different behavior depending where it shows up in a bracket expression. Consider ], and ^ as well.