Polish "Fix shellcheck warnings in CLI's bash script"

Closes gh-11458

spring-boot-project/spring-boot-cli/src/main/executablecontent/bin/spring

@@ -36,14 +36,14 @@ if [ -z "${JAVA_HOME}" ]; then
 			export JAVA_HOME="/System/Library/Frameworks/JavaVM.framework/Home"
 		fi
 	else
-		javaExecutable="$(which javac)"
+		javaExecutable="$(command -v javac)"
 		if [[ -z "$javaExecutable" || "$(expr "${javaExecutable}" : '\([^ ]*\)')" = "no" ]]; then
 			echo "JAVA_HOME not set and cannot find javac to deduce location, please set JAVA_HOME."
 			exit 1
 		fi
 		# readlink(1) is not available as standard on Solaris 10.
-		readLink=(which readlink)
-		[ $(expr "$readLink" : '\([^ ]*\)') = "no" ] && {
+		readLink="$(command -v readlink)"
+		[ "$(expr "${readLink}" : '\([^ ]*\)')" = "no" ] && {
 			echo "JAVA_HOME not set and readlink not available, please set JAVA_HOME."
 			exit 1
 		}
@@ -87,10 +87,10 @@ if [ -z "${SPRING_HOME}" ]; then
 		fi
 	done
 	SAVED="$(pwd)"
-    cd "$(dirname "${PRG}")/../" >&-
+	cd "$(dirname "${PRG}")/../" >&- || exit 1
 	SPRING_HOME="$(pwd -P)"
 	export SPRING_HOME
-    cd "$SAVED" >&-
+	cd "$SAVED" >&- || exit 1
 fi
 
 if [ ! -d "${SPRING_HOME}" ]; then
@@ -103,7 +103,7 @@ CLASSPATH=.:${SPRING_HOME}/bin
 if [ -d "${SPRING_HOME}/ext" ]; then
 	CLASSPATH=$CLASSPATH:${SPRING_HOME}/ext
 fi
-for f in ${SPRING_HOME}/lib/*; do
+for f in "${SPRING_HOME}"/lib/*; do
 	CLASSPATH=$CLASSPATH:$f
 done
 
@@ -112,4 +112,5 @@ if $cygwin; then
 	CLASSPATH=$(cygpath --path --mixed "$CLASSPATH")
 fi
 
-"${JAVA_HOME}/bin/java" ${JAVA_OPTS} -cp "$CLASSPATH" org.springframework.boot.loader.JarLauncher "$@"
+IFS=" " read -r -a javaOpts <<< "$JAVA_OPTS"
+"${JAVA_HOME}/bin/java" "${javaOpts[@]}" -cp "$CLASSPATH" org.springframework.boot.loader.JarLauncher "$@"