batch: FINDSTR regular expression not work

Question

echo a.txt| FINDSTR /R ".+\.txt$"

not work and not even:

echo a.txt| FINDSTR /R .+\.txt$

Why?

Edit:

Now works!

echo a.txt| FINDSTR /R ..*\.txt$

Answer 1

a) There is no + in the regex of Findstr. Use * instead. ..* should be the correct replacement for .+ .

b) There can be invisible character before the end of the line, eg caused by echo if there's a trailing space before | . Add another . before the line end to cover that.

C:\> echo a.txt | findstr /r ".*\.txt.$"
a.txt

It's also possible without the quotation marks.