redirect stderr to a file in call-process-region

Question

I have been reading the documentation for call-process-region here and I am trying to redirect stderr to a file. from the the documentation, this looks correct

(call-process-region beg end perltidy-executable t '(t (:file "/tmp/tidy")))

however when I try to run it I get the following error

Wrong type argument: stringp, (:file "/tmp/tidy")

it works without errors if I use

(call-process-region beg end perltidy-executable t '(t nil))

but that causes stderr to be lost.

What am I doing wrong here?

Answer 1

You don't need the (:file ) just give the error file as second element in the list.

BUFFER can also have the form (REAL-BUFFER STDERR-FILE); in that case,
REAL-BUFFER says what to do with standard output, as above,
while STDERR-FILE says what to do with standard error in the child.

So you would call:

(call-process-region beg end perltidy-executable t '(t "/tmp/tidy"))