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From the expr man page:
Pattern matches return the string matched between \( and \) or null; if \( and \) are not used, they return the number of characters matched or 0.
so it is printing a blank line because your expression is not matching anything (null). I think it is because you've made a mistake in your expression - I think you want [0-9] not [0.9]. I suspect you also mean [A-Z] instead of [A.Z].
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