Address some shellcheck issues

Author: jgarber623-cargosense

src/shellcheck/install.sh

@@ -5,13 +5,13 @@ set -e
 SHELLCHECK_VERSION="${VERSION:-"os-provided"}"
 INSTALL_PATH="${INSTALLPATH:-"/usr/local/bin"}"
 
-if [ "$(id -u)" -ne 0 ]; then
+if [[ "$(id -u)" -ne 0 ]]; then
   printf 'Script must be run as root. Use sudo, su, or add "USER root" to your Dockerfile before running this script.'
   exit 1
 fi
 
 
-if [ "${SHELLCHECK_VERSION}" = "os-provided" ]; then
+if [[ "${SHELLCHECK_VERSION}" = "os-provided" ]]; then
   apt update --yes
   apt install --no-install-recommends --yes shellcheck
 
@@ -27,8 +27,8 @@ if ! type curl >/dev/null 2>&1; then
   curl_installed="true"
 fi
 
-if [ "${SHELLCHECK_VERSION}" = "latest" ]; then
-  SHELLCHECK_VERSION=$(curl -s --head https://github.com/koalaman/shellcheck/releases/latest | sed -nr 's/location:.*\/v(.+)/\1/ip' | tr -d '\r')
+if [[ "${SHELLCHECK_VERSION}" = "latest" ]]; then
+  SHELLCHECK_VERSION="$(curl -s --head https://github.com/koalaman/shellcheck/releases/latest | sed -nr 's/location:.*\/v(.+)/\1/ip' | tr -d '\r')"
 fi
 
 machine="$(uname -m)"
@@ -47,6 +47,6 @@ url="https://github.com/koalaman/shellcheck/releases/download/v${SHELLCHECK_VERS
 
 curl -sSL "${url}" | tar --strip-components=1 -Jxvf - -C "${INSTALL_PATH}" "shellcheck-v${SHELLCHECK_VERSION}/shellcheck"
 
-if [ -n "${curl_installed}" ]; then
+if [[ -n "${curl_installed}" ]]; then
   apt purge curl --autoremove --yes
 fi