Is the regular expression [a-Z] valid and if yes then is it the same as [a-zA-Z]?

Question

Is the regular expression [a-Z] valid and if yes then is it the same as [a-zA-Z]? Please note that in [a-Z] the a is lowercase and the Z is uppercase.

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Answer 1

I've just fallen over this in a script (not my own).

It seems that grep, awk, sed accept [a-Z] based on your locale (i.e. LANG or LC_CTYPE environment variable). In POSIX, [a-Z] isn't allowed by these tools, but in some other locales (e.g. en_gb.utf8) it works, and is the same as [a-zA-Z].

Yes, I've checked, it doesn't match any of _^[]`.

Given that this has taken quite some time to debug, I strongly discourage anyone from ever using [a-Z] in a regex.