is [0-9a-fA-F] the same as [0-9a-f-A-F]?

Question

Are these two equivalent? [0-9a-fA-F] and [0-9a-f-A-F]

I've been trying these two regexes with egrep in some texts and they seem to be equivalent. Is there a case they won't be return same results?

Also, in the second expression, what is the meaning of the second - and why would I need it? I am bit confused with these simple examples.

Answer 1

The second expression also matches a dash as well as hexadecimals

Edit in egrep, which is what you're using the second one is in fact invalid:

# echo "12345678" | egrep '^[0-9a-f-A-F]+$'
egrep: Invalid range end

The correct expression for the second is by ending with a dash:

[0-9a-fA-F-]