Schemantic error in verification no system-ruby packages installed Dockerfile

[clushie]

This line

ruby/Dockerfile-slim.template

Lines 101 to 102 in e040029

	# verify we have no "ruby" packages installed
	! dpkg -l | grep -i ruby; \

won't work as expected. Because of the ! it will always succeed.

Shellcheck tracks this behavior with

! dpkg -l | grep -i ruby
^-- SC2251: This ! is not on a condition and skips errexit. Use `&& exit 1` instead, or make sure $? is checked.

I can't see a clean one-liner to solve this, I think the correct way is to rather run:

if dpkg -l | grep -i 'ruby'; then return 1; fi

also dpkg -l can list previously uninstalled packages, to verify a package is actually installed it would rather be | grep -iP '^ii.*ruby.*'

[tianon]

Just to tug on #342 (comment) (trust, but verify):

(Also, IMO it's worth verifying that the current code actually does fail to exit properly when ruby is installed.)

I tried this out with the following diff:

Diff:

diff --git a/3.0/alpine3.13/Dockerfile b/3.0/alpine3.13/Dockerfile
index 77dabff..731d56d 100644
--- a/3.0/alpine3.13/Dockerfile
+++ b/3.0/alpine3.13/Dockerfile
@@ -103,6 +103,7 @@ RUN set -eux; \
                procps \
                yaml-dev \
                zlib-dev \
+               ruby \
        ; \
        apk del --no-network .ruby-builddeps; \
        \
diff --git a/3.0/buster/Dockerfile b/3.0/buster/Dockerfile
index 0f81bb7..b4b0e90 100644
--- a/3.0/buster/Dockerfile
+++ b/3.0/buster/Dockerfile
@@ -56,7 +56,7 @@ RUN set -eux; \
        make install; \
        \
        apt-mark auto '.*' > /dev/null; \
-       apt-mark manual $savedAptMark > /dev/null; \
+       apt-mark manual $savedAptMark ruby > /dev/null; \
        find /usr/local -type f -executable -not \( -name '*tkinter*' \) -exec ldd '{}' ';' \
                | awk '/=>/ { print $(NF-1) }' \
                | sort -u \

(The build does indeed succeed! 😱 😞 👍)

Edit: as noted in my comment there, my preference is to just upgrade this to if ... | grep -i ruby; then exit 1; fi