Why does findstr not handle case properly (in some circumstances)?

Question

While writing some recent scripts in cmd.exe, I had a need to use findstr with regular expressions - customer required standard cmd.exe commands (no GnuWin32 nor Cygwin nor VBS nor Powershell).

I just wanted to know if a variable contained any upper-case characters and attempted to use:

> set myvar=abc
> echo %myvar%|findstr /r "[A-Z]"
abc
> echo %errorlevel%
0

When %myvar% is set to abc, that actually outputs the string and sets errorlevel to 0, saying that a match was found.

However, the full-list variant:

> echo %myvar%|findstr /r "[ABCDEFGHIJKLMNOPQRSTUVWXYZ]"
> echo %errorlevel%
1

does not output the line and it correctly sets errorlevel to 1.

In addition:

> echo %myvar%|findstr /r "^[A-Z]*$"
> echo %errorlevel%
1

also works as expected.

I'm obviously missing something here even if it's only the fact that findstr is somehow broken.

Why does the first (range) regex not work in this case?

---

And yet more weirdness:

> echo %myvar%|findstr /r "[A-Z]"
abc
> echo %myvar%|findstr /r "[A-Z][A-Z]"
abc
> echo %myvar%|findstr /r "[A-Z][A-Z][A-Z]"
> echo %myvar%|findstr /r "[A]"

The last two above also does not output the string!!

Answer 1

This appears to be a bug caused by the use of ranges within regular expression searches.

It doesn't occur for the first character in the range. It doesn't occur at all for non-ranges.

> echo a | findstr /r "[A-C]"
> echo b | findstr /r "[A-C]"
    b
> echo c | findstr /r "[A-C]"
    c
> echo d | findstr /r "[A-C]"
> echo b | findstr /r "[B-C]"
> echo c | findstr /r "[B-C]"
    c

> echo a | findstr /r "[ABC]"
> echo b | findstr /r "[ABC]"
> echo c | findstr /r "[ABC]"
> echo d | findstr /r "[ABC]"
> echo b | findstr /r "[BC]"
> echo c | findstr /r "[BC]"

> echo A | findstr /r "[A-C]"
    A
> echo B | findstr /r "[A-C]"
    B
> echo C | findstr /r "[A-C]"
    C
> echo D | findstr /r "[A-C]"

To get around the problem, I simply used specific ranges ([ABCD] instead of [A-D]). A more sensible approach for those that are allowed would be to download CygWin or GnuWin32 and use grep from one of those packages..