How to redirect the output of `apt-file update` into a file?

I have a zsh function which updates my system (.deb packages, pip packages, texlive packages, ...).

.deb

pip

It looks like this:

up()

The last line calls the __update_system function and pipes its output to tee, which in turn should display the output on the terminal, and append it to a file, so that I can review it later if something went wrong.

__update_system

tee

One of the commands executed by __update_system is:

__update_system

$ apt-file update

It seems to be executed, but its output is not logged in the file.
All the other commands (including aptitude update) are logged.

aptitude update

I tried to understand by executing this command in a shell:

$ apt-file update >/tmp/log

Again, apt-file update seems to be executed, but the output is not logged as /tmp/log is empty.

apt-file update

/tmp/log

I thought that maybe the output is sent on the standard error, so I tried:

$ apt-file update >/tmp/log 2>&1

But I got the same result, an empty file.

I tried in bash, which also gave me an empty file.

Here are some details about my system:

$ uname -a Linux ubuntu 4.4.0-135-generic #161-Ubuntu SMP Mon Aug 27 10:45:01 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

About zsh:

$ zsh --version zsh 5.5.1-dev-0 (x86_64-pc-linux-gnu)

About bash:

$ bash --version GNU bash, version 4.4.0(1)-release (x86_64-unknown-linux-gnu)

About apt-file:

apt-file

$ aptitude show apt-file Package: apt-file State: installed Automatically installed: no Version: 2.5.5ubuntu1 Priority: optional Section: universe/admin Maintainer: Ubuntu Developers <ubuntu-devel-discuss@lists.ubuntu.com> Architecture: all Uncompressed Size: 92,2 k Depends: perl, curl, libconfig-file-perl, libapt-pkg-perl, liblist-moreutils-perl, libregexp-assemble-perl, libfile-temp-perl Suggests: openssh-client, sudo Description: search for files within Debian packages (command-line interface) apt-file is a command line tool for searching files contained in packages for the APT packaging system. You can search in which package a file is included or list the contents of a package without installing or fetching it.