Enable shellcheck and fix warnings

.github/workflows/ci.yml

@@ -23,3 +23,12 @@ jobs:
         uses: actions/checkout@v4
       - name: Functional tests on heroku:${{ matrix.stack_number }}-build
         run: test/run
+
+  shell-lint:
+    runs-on: ubuntu-22.04
+    container:
+      image: koalaman/shellcheck-alpine:v0.9.0
+    steps:
+      - uses: actions/checkout@v4
+      - name: shellcheck
+        run: shellcheck -x bin/compile bin/detect bin/release bin/report

Makefile

@@ -1,5 +1,8 @@
 test: heroku-22-build heroku-20-build
 
+shellcheck:
+	@shellcheck -x bin/compile bin/detect bin/release bin/report
+
 heroku-22-build:
 	@echo "Running tests in docker (heroku-22-build)..."
 	@docker run -v $(shell pwd):/buildpack:ro --rm -it -e "STACK=heroku-22" heroku/heroku:22-build bash -c 'cp -r /buildpack /buildpack_test; cd /buildpack_test/; test/run;'

bin/compile

@@ -69,7 +69,7 @@ else
   # like>>    :repo:deb http://cz.archive.ubuntu.com/ubuntu artful main universe
   if grep -q -e "^:repo:" "$BUILD_DIR/Aptfile"; then
     topic "Adding custom repositories"
-    cat "$BUILD_DIR/Aptfile" | grep -s -e "^:repo:" | sed 's/^:repo:\(.*\)\s*$/\1/g' >> "$APT_SOURCES"
+    grep -s -e "^:repo:" "$BUILD_DIR/Aptfile" | sed 's/^:repo:\(.*\)\s*$/\1/g' >> "$APT_SOURCES"
   fi
 fi
 
@@ -80,7 +80,7 @@ APT_OPTIONS+=("-o" "dir::etc::sourcelist=$APT_SOURCES" "-o" "dir::etc::sourcepar
 topic "Updating apt caches"
 apt-get "${APT_OPTIONS[@]}" update 2>&1 | indent
 
-for PACKAGE in $(cat "$BUILD_DIR/Aptfile" | grep -v -s -e '^#' | grep -v -s -e "^:repo:"); do
+while IFS= read -r PACKAGE; do
   if [[ $PACKAGE == *deb ]]; then
     PACKAGE_NAME=$(basename "$PACKAGE" .deb)
     PACKAGE_FILE=$APT_CACHE_DIR/archives/$PACKAGE_NAME.deb
@@ -91,7 +91,7 @@ for PACKAGE in $(cat "$BUILD_DIR/Aptfile" | grep -v -s -e '^#' | grep -v -s -e "
     topic "Fetching .debs for $PACKAGE"
     apt-get "${APT_OPTIONS[@]}" -y "${APT_FORCE_YES[@]}" -d install --reinstall "$PACKAGE" | indent
   fi
-done
+done < <(grep --invert-match -e "^#" -e "^\s*$" -e "^:repo:" "${BUILD_DIR}/Aptfile")
 
 mkdir -p "$BUILD_DIR/.apt"