base-files: replace backticks by $(...)

This replaces deprecated backticks by more versatile $(...) syntax.

This does not touch lib/upgrade/nand.sh, as there replacement is
not trivial.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

package/base-files/files/bin/board_detect

@@ -5,7 +5,7 @@ CFG=$1
 [ -n "$CFG" ] || CFG=/etc/board.json
 
 [ -d "/etc/board.d/" -a ! -s "$CFG" ] && {
-	for a in `ls /etc/board.d/*`; do
+	for a in $(ls /etc/board.d/*); do
 		[ -x $a ] || continue;
 		$(. $a)
 	done

package/base-files/files/etc/uci-defaults/13_fix-group-user

 . /lib/functions.sh
 
-for file in `grep -sl Require-User /usr/lib/opkg/info/*.control`; do
+for file in $(grep -sl Require-User /usr/lib/opkg/info/*.control); do
 	file="${file##*/}"
 	file="${file%.control}"
 	add_group_and_user "${file}"

package/base-files/files/lib/preinit/30_failsafe_wait

@@ -91,7 +91,7 @@ failsafe_wait() {
 	grep -q 'failsafe=' /proc/cmdline && FAILSAFE=true && export FAILSAFE
 	if [ "$FAILSAFE" != "true" ]; then
 		fs_wait_for_key f 'to enter failsafe mode' $fs_failsafe_wait_timeout && FAILSAFE=true
-		[ -f "/tmp/failsafe_button" ] && FAILSAFE=true && echo "- failsafe button "`cat /tmp/failsafe_button`" was pressed -"
+		[ -f "/tmp/failsafe_button" ] && FAILSAFE=true && echo "- failsafe button "$(cat /tmp/failsafe_button)" was pressed -"
 		[ "$FAILSAFE" = "true" ] && export FAILSAFE && touch /tmp/failsafe
 	fi
 }

package/base-files/files/sbin/pkg_check

@@ -72,14 +72,14 @@ while [ "$1" ]; do
 	fi
 	[ $QUIET = yes ] || echo " * Checking package $1:"
 	ERR=""
-	CHECK="`sha256sum -c /usr/lib/opkg/info/$1.files-sha256sum 2> /dev/null`"
+	CHECK="$(sha256sum -c /usr/lib/opkg/info/$1.files-sha256sum 2> /dev/null)"
 
 	# Are the changed files config files?
-	if [ $? -ne 0 ] && [ "`cat "/usr/lib/opkg/info/$1.files-sha256sum"`" ]; then
-		NEWCHECK="`echo "$CHECK" | grep '^.*: OK$'`"
-		for i in `echo "$CHECK" | sed -n 's|^\(.*\): FAILED$|\1|p'`; do
-			if [ "`grep "^$i\$" "/usr/lib/opkg/info/$1.conffiles" 2> /dev/null`" ] || \
-			   [ "`echo "$i" | grep "^/etc/uci-defaults/"`" ]; then
+	if [ $? -ne 0 ] && [ "$(cat "/usr/lib/opkg/info/$1.files-sha256sum")" ]; then
+		NEWCHECK="$(echo "$CHECK" | grep '^.*: OK$')"
+		for i in $(echo "$CHECK" | sed -n 's|^\(.*\): FAILED$|\1|p'); do
+			if [ "$(grep "^$i\$" "/usr/lib/opkg/info/$1.conffiles" 2> /dev/null)" ] || \
+			   [ "$(echo "$i" | grep "^/etc/uci-defaults/")" ]; then
 				NEWCHECK="${NEWCHECK}${NL}${i}: CONFIGURED"
 			else
 				NEWCHECK="${NEWCHECK}${NL}${i}: FAILED"
@@ -91,7 +91,7 @@ while [ "$1" ]; do
 
 	# Do we have changed files or not?
 	if [ -z "$ERR" ]; then
-		[ $QUIET = yes ] || [ -z "`cat "/usr/lib/opkg/info/$1.files-sha256sum"`" ] || echo "$CHECK" | sed 's|^|   - |'
+		[ $QUIET = yes ] || [ -z "$(cat "/usr/lib/opkg/info/$1.files-sha256sum")" ] || echo "$CHECK" | sed 's|^|   - |'
 		[ $QUIET = yes ] || echo " * Package $1 is ok"
 		[ $QUIET = yes ] || echo
 	else
@@ -107,7 +107,7 @@ while [ "$1" ]; do
 			echo "Exiting on first change found!"
 			exit 1
 		fi
-		for i in `echo "$CHECK" | sed -n 's|^\(.*\): FAILED$|\1|p'`; do
+		for i in $(echo "$CHECK" | sed -n 's|^\(.*\): FAILED$|\1|p'); do
 			SUMMARY="${SUMMARY}${NL} - $1: $i"
 		done
 		echo