Use $(...) notation instead of legacy backtick notation for embedded shell commands

shellcheck reported

    SC2006: Use $(...) notation instead of legacy backticked `...`.

Fixed by applying shellcheck's diff output as a patch.

setup/bootstrap.sh

@@ -18,11 +18,11 @@ if [ -z "$TAG" ]; then
 	# space, but if we put it in a comment it would confuse the status checks!)
 	# to get the latest version, so the first such line must be the one that we
 	# want to display in status checks.
-	if [ "`lsb_release -d | sed 's/.*:\s*//' | sed 's/18\.04\.[0-9]/18.04/' `" == "Ubuntu 18.04 LTS" ]; then
+	if [ "$(lsb_release -d | sed 's/.*:\s*//' | sed 's/18\.04\.[0-9]/18.04/' )" == "Ubuntu 18.04 LTS" ]; then
 		# This machine is running Ubuntu 18.04.
 		TAG=v0.53
 
-	elif [ "`lsb_release -d | sed 's/.*:\s*//' | sed 's/14\.04\.[0-9]/14.04/' `" == "Ubuntu 14.04 LTS" ]; then
+	elif [ "$(lsb_release -d | sed 's/.*:\s*//' | sed 's/14\.04\.[0-9]/14.04/' )" == "Ubuntu 14.04 LTS" ]; then
 		# This machine is running Ubuntu 14.04.
 		echo "You are installing the last version of Mail-in-a-Box that will"
 		echo "support Ubuntu 14.04. If this is a new installation of Mail-in-a-Box,"
@@ -68,11 +68,11 @@ fi
 cd $HOME/mailinabox
 
 # Update it.
-if [ "$TAG" != `git describe` ]; then
+if [ "$TAG" != $(git describe) ]; then
 	echo Updating Mail-in-a-Box to $TAG . . .
 	git fetch --depth 1 --force --prune origin tag $TAG
 	if ! git checkout -q $TAG; then
-		echo "Update failed. Did you modify something in `pwd`?"
+		echo "Update failed. Did you modify something in $(pwd)?"
 		exit 1
 	fi
 	echo

setup/dns.sh

@@ -132,7 +132,7 @@ cat > /etc/cron.daily/mailinabox-dnssec << EOF;
 #!/bin/bash
 # Mail-in-a-Box
 # Re-sign any DNS zones with DNSSEC because the signatures expire periodically.
-`pwd`/tools/dns_update
+$(pwd)/tools/dns_update
 EOF
 chmod +x /etc/cron.daily/mailinabox-dnssec
 

setup/firstuser.sh

@@ -1,5 +1,5 @@
 # If there aren't any mail users yet, create one.
-if [ -z "`management/cli.py user`" ]; then
+if [ -z "$(management/cli.py user)" ]; then
 	# The outut of "management/cli.py user" is a list of mail users. If there
 	# aren't any yet, it'll be empty.
 
@@ -10,7 +10,7 @@ if [ -z "`management/cli.py user`" ]; then
 			input_box "Mail Account" \
 				"Let's create your first mail account.
 				\n\nWhat email address do you want?" \
-				me@`get_default_hostname` \
+				me@$(get_default_hostname) \
 				EMAIL_ADDR
 
 			if [ -z "$EMAIL_ADDR" ]; then

setup/mail-dovecot.sh

@@ -45,8 +45,8 @@ apt_install \
 # - https://www.dovecot.org/list/dovecot/2012-August/137569.html
 # - https://www.dovecot.org/list/dovecot/2011-December/132455.html
 tools/editconf.py /etc/dovecot/conf.d/10-master.conf \
-	default_process_limit=$(echo "`nproc` * 250" | bc) \
-	default_vsz_limit=$(echo "`free -tm  | tail -1 | awk '{print $2}'` / 3" | bc)M \
+	default_process_limit=$(echo "$(nproc) * 250" | bc) \
+	default_vsz_limit=$(echo "$(free -tm  | tail -1 | awk '{print $2}') / 3" | bc)M \
 	log_path=/var/log/mail.log
 
 # The inotify `max_user_instances` default is 128, which constrains

setup/management.sh

@@ -97,7 +97,7 @@ export LANG=en_US.UTF-8
 export LC_TYPE=en_US.UTF-8
 
 source $venv/bin/activate
-exec python `pwd`/management/daemon.py
+exec python $(pwd)/management/daemon.py
 EOF
 chmod +x $inst_dir/start
 cp --remove-destination conf/mailinabox.service /lib/systemd/system/mailinabox.service # target was previously a symlink so remove it first
@@ -112,7 +112,7 @@ minute=$((RANDOM % 60))  # avoid overloading mailinabox.email
 cat > /etc/cron.d/mailinabox-nightly << EOF;
 # Mail-in-a-Box --- Do not edit / will be overwritten on update.
 # Run nightly tasks: backup, status checks.
-$minute 3 * * *	root	(cd `pwd` && management/daily_tasks.sh)
+$minute 3 * * *	root	(cd $(pwd) && management/daily_tasks.sh)
 EOF
 
 # Start the management server.

setup/nextcloud.sh

@@ -128,7 +128,7 @@ if [ ! -d /usr/local/lib/owncloud/ ] || [[ ! ${CURRENT_NEXTCLOUD_VER} =~ ^$nextc
 
 	# Backup the existing ownCloud/Nextcloud.
 	# Create a backup directory to store the current installation and database to
-	BACKUP_DIRECTORY=$STORAGE_ROOT/owncloud-backup/`date +"%Y-%m-%d-%T"`
+	BACKUP_DIRECTORY=$STORAGE_ROOT/owncloud-backup/$(date +"%Y-%m-%d-%T")
 	mkdir -p "$BACKUP_DIRECTORY"
 	if [ -d /usr/local/lib/owncloud/ ]; then
 		echo "Upgrading Nextcloud --- backing up existing installation, configuration, and database to directory to $BACKUP_DIRECTORY..."

setup/preflight.sh

@@ -8,7 +8,7 @@ if [[ $EUID -ne 0 ]]; then
 fi
 
 # Check that we are running on Ubuntu 18.04 LTS (or 18.04.xx).
-if [ "`lsb_release -d | sed 's/.*:\s*//' | sed 's/18\.04\.[0-9]/18.04/' `" != "Ubuntu 18.04 LTS" ]; then
+if [ "$(lsb_release -d | sed 's/.*:\s*//' | sed 's/18\.04\.[0-9]/18.04/' )" != "Ubuntu 18.04 LTS" ]; then
 	echo "Mail-in-a-Box only supports being installed on Ubuntu 18.04, sorry. You are running:"
 	echo
 	lsb_release -d | sed 's/.*:\s*//'

setup/start.sh

@@ -46,7 +46,7 @@ fi
 # in the first dialog prompt, so we should do this before that starts.
 cat > /usr/local/bin/mailinabox << EOF;
 #!/bin/bash
-cd `pwd`
+cd $(pwd)
 source setup/start.sh
 EOF
 chmod +x /usr/local/bin/mailinabox

setup/webmail.sh

@@ -47,7 +47,7 @@ needs_update=0 #NODOC
 if [ ! -f /usr/local/lib/roundcubemail/version ]; then
 	# not installed yet #NODOC
 	needs_update=1 #NODOC
-elif [[ "$UPDATE_KEY" != `cat /usr/local/lib/roundcubemail/version` ]]; then
+elif [[ "$UPDATE_KEY" != $(cat /usr/local/lib/roundcubemail/version) ]]; then
 	# checks if the version is what we want
 	needs_update=1 #NODOC
 fi

setup/zpush.sh

@@ -27,7 +27,7 @@ TARGETHASH=4b312d64227ef887b24d9cc8f0ae17519586f6e2
 needs_update=0 #NODOC
 if [ ! -f /usr/local/lib/z-push/version ]; then
 	needs_update=1 #NODOC
-elif [[ $VERSION != `cat /usr/local/lib/z-push/version` ]]; then
+elif [[ $VERSION != $(cat /usr/local/lib/z-push/version) ]]; then
 	# checks if the version
 	needs_update=1 #NODOC
 fi