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 gr

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.

Answer 2

Remember that - is a range operator, so \-\ matches any character in the range \ to \, which is exactly a \.

If you move it to the end, it'll loose its meaning as a range, that's why it works.