Fix linting and static analysis

Set linter and formatter to *only* run when files it works for are
actually detected. Uses moreutils' ifne to detect the status of stdin
before sending an empty string to the test suite.

.gitlab-ci.yml

@@ -1,29 +1,30 @@
 ---
-# This file is a template, and might need editing before it works on your project.
+# install moreutils to enable ifne (if not empty)
-# see https://docs.gitlab.com/ce/ci/yaml/README.html for all available options
+# will only run the respective analyzers when files to test
-
+# are acutally found
-# you can delete this line if you're not using Docker
 image: fnichol/check-shell:latest
 
 analyze:
   stage: test
   before_script:
+    - apk add moreutils
     - shellcheck --version
   script:
     - echo "--------- CHECKING POSIX SHELLSCRIPTS -------------"
-    - find . -type f -name '*.sh' | xargs shellcheck -Calways
+    - find . -type f -name '*.sh' | ifne xargs shellcheck -Calways
     - echo "--------- CHECKING ZSH SHELLSCRIPTS -------------"
-    - find . -type f -name '*.zsh' | xargs shellcheck -Calways -s bash -e SC2034
+    - find . -type f -name '*.zsh' | ifne xargs shellcheck -Calways -s bash -e SC2034
 
 lint:
   stage: test
   before_script:
+    - apk add moreutils
     - shfmt -version
   script:
     - echo "--------- CHECKING POSIX SHELLSCRIPTS -------------"
-    - find . -type f -name '*.sh' | xargs shfmt -d -i 2
+    - find . -type f -name '*.sh' | ifne xargs shfmt -d -i 2
     - echo "--------- CHECKING ZSH SHELLSCRIPTS -------------"
-    - find . -type f -name '*.zsh' | xargs shfmt -d -i 2
+    - find . -type f -name '*.zsh' | ifne xargs shfmt -d -i 2
 
 test:
   stage: test