fix shellcheck warnings and errors

build-samples/build_samples.sh

@@ -2,15 +2,15 @@
 
 set -euo pipefail
 
-THISDIR="$(cd $(dirname $0) && pwd)"
+THISDIR="$(cd $(dirname "$0") && pwd)"
 
 source "${THISDIR}"/../helpers.sh
 
 VMLINUX_BTF="$1"
 KERNEL="$2"
 TOOLCHAIN="$3"
 
-LLVM_VER="$(llvm_version $TOOLCHAIN)" && :
+LLVM_VER="$(llvm_version "$TOOLCHAIN")" && :
 if [ $? -eq 0 ]; then
 	export LLVM="-$LLVM_VER"
 fi
@@ -25,16 +25,16 @@ fi
 
 make headers_install
 make \
-	CLANG=clang-${LLVM_VER} \
-	OPT=opt-${LLVM_VER} \
-	LLC=llc-${LLVM_VER} \
-	LLVM_DIS=llvm-dis-${LLVM_VER} \
-	LLVM_OBJCOPY=llvm-objcopy-${LLVM_VER} \
-	LLVM_READELF=llvm-readelf-${LLVM_VER} \
-	LLVM_STRIP=llvm-strip-${LLVM_VER} \
+	CLANG="clang-${LLVM_VER}" \
+	OPT="opt-${LLVM_VER}" \
+	LLC="llc-${LLVM_VER}" \
+	LLVM_DIS="llvm-dis-${LLVM_VER}" \
+	LLVM_OBJCOPY="llvm-objcopy-${LLVM_VER}" \
+	LLVM_READELF="llvm-readelf-${LLVM_VER}" \
+	LLVM_STRIP="llvm-strip-${LLVM_VER}" \
 	VMLINUX_BTF="${VMLINUX_BTF}" \
 	VMLINUX_H="${VMLINUX_H}" \
 	-C "${REPO_ROOT}/${REPO_PATH}/samples/bpf" \
-	-j $((4*$(nproc)))
+	-j "$((4*$(nproc)))"
 
 foldable end build_samples

helpers.sh

@@ -1,3 +1,5 @@
+# shellcheck shell=ksh
+
 # $1 - start or end
 # $2 - fold identifier, no spaces
 # $3 - fold section description

prepare-rootfs/run.sh

@@ -438,7 +438,7 @@ chmod 644 /exitstatus
 HERE
 
 # Create the init scripts.
-if [[ ! -z SETUPCMD ]]; then
+if [[ -n "$SETUPCMD" ]]; then
 	# Unescape whitespace characters.
 	setup_cmd=$(sed 's/\(\\\)\([[:space:]]\)/\2/g' <<< "${SETUPCMD}")
 	kernel="${KERNELRELEASE}"