Turn shellcheck into a normal make target. Fix new files it caught

This checks every file it checked (and a few more),
but explicitly instead of "if it works it works" best-effort
(which wasn't that good anyway)

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #10512
Closes #12101

contrib/initramfs/scripts/zfs

@@ -5,6 +5,8 @@
 #
 # Enable this by passing boot=zfs on the kernel command line.
 #
+# $quiet, $root, $rpool, $bootfs come from the cmdline:
+# shellcheck disable=SC2154
 
 # Source the common functions
 . /etc/zfs/zfs-functions
@@ -102,14 +104,10 @@ find_rootfs()
 # Support function to get a list of all pools, separated with ';'
 find_pools()
 {
-	CMD="$*"
-
-	pools=$($CMD 2> /dev/null | \
+	pools=$("$@" 2> /dev/null | \
 		grep -E "pool:|^[a-zA-Z0-9]" | \
 		sed 's@.*: @@' | \
-		while read -r pool; do \
-		    printf "%s" "$pool;"
-		done)
+		tr '\n' ';')
 
 	echo "${pools%%;}" # Return without the last ';'.
 }
@@ -203,7 +201,7 @@ import_pool()
 	# exists).
 	if [ -n "$USE_DISK_BY_ID" ] && [ -z "$ZPOOL_IMPORT_PATH" ]
 	then
-		dirs="$(for dir in $(echo /dev/disk/by-*)
+		dirs="$(for dir in /dev/disk/by-*
 		do
 			# Ignore by-vdev here - we want it first!
 			echo "$dir" | grep -q /by-vdev && continue
@@ -329,6 +327,7 @@ mount_fs()
 
 	# Need the _original_ datasets mountpoint!
 	mountpoint=$(get_fs_value "$fs" mountpoint)
+	ZFS_CMD="mount -o zfsutil -t zfs"
 	if [ "$mountpoint" = "legacy" ] || [ "$mountpoint" = "none" ]; then
 		# Can't use the mountpoint property. Might be one of our
 		# clones. Check the 'org.zol:mountpoint' property set in
@@ -348,15 +347,11 @@ mount_fs()
 			fi
 		fi
 
+		# If it's not a legacy filesystem, it can only be a
+		# native one...
 		if [ "$mountpoint" = "legacy" ]; then
 			ZFS_CMD="mount -t zfs"
-		else
-			# If it's not a legacy filesystem, it can only be a
-			# native one...
-			ZFS_CMD="mount -o zfsutil -t zfs"
 		fi
-	else
-		ZFS_CMD="mount -o zfsutil -t zfs"
 	fi
 
 	# Possibly decrypt a filesystem using native encryption.
@@ -553,7 +548,6 @@ rollback_snap()
 ask_user_snap()
 {
 	fs="$1"
-	i=1
 
 	# We need to temporarily disable debugging. Set 'debug' so we
 	# remember to enabled it again.
@@ -566,16 +560,25 @@ ask_user_snap()
 	# Because we need the resulting snapshot, which is sent on
 	# stdout to the caller, we use stderr for our questions.
 	echo "What snapshot do you want to boot from?" > /dev/stderr
-	while read -r snap; do
-	    echo "  $i: ${snap}" > /dev/stderr
-	    eval "$(echo SNAP_$i=$snap)"
-	    i=$((i + 1))
-	done <<EOT
-$("${ZFS}" list -H -oname -tsnapshot -r "${fs}")
-EOT
+	# shellcheck disable=SC2046
+	IFS="
+" set -- $("${ZFS}" list -H -oname -tsnapshot -r "${fs}")
 
-	echo "%s" "  Snap nr [1-$((i-1))]? " > /dev/stderr
-	read -r snapnr
+	i=1
+	for snap in "$@"; do
+		echo "  $i: $snap"
+		i=$((i + 1))
+	done > /dev/stderr
+
+	# expr instead of test here because [ a -lt 0 ] errors out,
+	# but expr falls back to lexicographical, which works out right
+	snapnr=0
+	while expr "$snapnr" "<" 1 > /dev/null ||
+	    expr "$snapnr" ">" "$#" > /dev/null
+	do
+		printf "%s" "Snap nr [1-$#]? " > /dev/stderr
+		read -r snapnr
+	done
 
 	# Re-enable debugging.
 	if [ -n "${debug}" ]; then
@@ -583,7 +586,7 @@ EOT
 		set -x
 	fi
 
-	echo "$(eval echo '$SNAP_'$snapnr)"
+	eval echo '$'"$snapnr"
 }
 
 setup_snapshot_booting()
@@ -703,7 +706,7 @@ mountroot()
 
 	# ------------
 	# Look for the cache file (if any).
-	[ ! -f ${ZPOOL_CACHE} ] && unset ZPOOL_CACHE
+	[ ! -f "${ZPOOL_CACHE}" ] && unset ZPOOL_CACHE
 
 	# ------------
 	# Compatibility: 'ROOT' is for Debian GNU/Linux (etc),
@@ -793,7 +796,8 @@ mountroot()
 		#
 		# Reassign the variable by dumping the environment and
 		# stripping the zfs-bootfs= prefix.  Let the shell handle
-		# quoting through the eval command.
+		# quoting through the eval command:
+		# shellcheck disable=SC2046
 		eval ZFS_RPOOL=$(set | sed -n -e 's,^zfs-bootfs=,,p')
 	fi
 
@@ -947,7 +951,7 @@ mountroot()
 
 	touch /run/zfs_unlock_complete
 	if [ -e /run/zfs_unlock_complete_notify ]; then
-		read -r zfs_unlock_complete_notify < /run/zfs_unlock_complete_notify
+		read -r < /run/zfs_unlock_complete_notify
 	fi
 
 	# ------------