Add sh file checks and fix lints

Author: MareStare

docker/app/purge-cache

@@ -7,9 +7,9 @@
 #
 # {"files":[]}
 
-body="$1"
-api_token=
-zone_id=
+# body="$1"
+# api_token=
+# zone_id=
 
 # curl -XPOST \
 #      -H "Content-Type: application/json" \

docker/app/run-test

@@ -11,10 +11,10 @@ mix format --check-formatted
 
 # Sleep to allow OpenSearch to finish initializing
 # if it's not done doing whatever it does yet
-echo -n "Waiting for OpenSearch"
+printf "Waiting for OpenSearch"
 
 until wget -qO - opensearch:9200; do
-  echo -n "."
+  printf "."
   sleep 2
 done
 

scripts/shellcheck.sh

@@ -1,4 +1,12 @@
 #!/usr/bin/env bash
+#
+# This script runs shellcheck on all shell scripts in the repository.
+# It exists because shellcheck doesn't attempt to automatically discover
+# shell scripts and requires specifying the files paths explicitly.
+#
+# This is somewhat understandable, because not all shell scripts use
+# obvious file extensions like `.sh`. So, we discover such files by
+# checking if they have one of the expected shebang lines at the beginning.
 
 set -euo pipefail
 
@@ -7,6 +15,7 @@ set -euo pipefail
 function shell_script_files {
   git ls-files "*.sh"
   git grep --files-with-matches '^#!/usr/bin/env bash'
+  git grep --files-with-matches '^#!/usr/bin/env sh'
 }
 
 mapfile -t files < <(shell_script_files "$@" | sort --unique)