How to make grep [A-Z] independent of locale?

Question

I was doing some everyday grepping and suddenly discovered that something seemingly trivial does not work:

$ echo T | grep [A-Z]

No match.

How come T is not within A-Z range?

I changed the regex a tiny bit:

$ echo T | grep [A-Y]

A match!

Whoa! How is T within A-Y but not within A-Z?

Apparently this is because my environment is set to Estonian locale where Y is at the end of the alphabet but Z is somewhere in the middle: ABCDEFGHIJKLMNOPQRSŠZŽTUVWÕÄÖÜXY

$ echo $LANG
et_EE.UTF-8

This all came as a bit of a shock to me. 99% of the time I grep computer code, not Estonian literature. Have I been using grep the wrong way all the time? What all kind of mistakes have I made because of this in the past?

After trying several things I arrived at the following solution:

$ echo T | LANG=C grep [A-Z]

Is this the recommended way to make grep locale-independent?

Further more... would it be safe to define an alias like that:

$ alias grep="LANG=C grep"

PS. I'm also wondering of why are the character ranges like [A-Z] locale dependent in the first place while \w seems to be unaffected by locale (although the manual says \w is equivalent of [[:alnum:]] - but I found out the latter depends on locale while \w does not).

Answer 1

POSIX regular expressions, which Linux and FreeBSD grep support naturally, and some others support on request, have a series of [:xxx:] patterns that honor locales. See the man page for details.

   grep '[[:upper:]]' 

As the []s are part of the pattern name you need the outer [] as well, regardless of how strange it looks.

With the advent of these : codes the classic \w, etc., remain strictly in the C locale. Thus your choice of patterns determines if grep uses the current locale or not.

[A-Z] should follow locale, but you may need to set LC_ALL rather than LANG, especially if the system sets LC_ALL to a different value for your.