diff --git a/github-dev/cleanup-pr-branch b/github-dev/cleanup-pr-branch
index 3af2446..4a28a96 100755
--- a/github-dev/cleanup-pr-branch
+++ b/github-dev/cleanup-pr-branch
@@ -2,7 +2,7 @@
 set -e
 set -o pipefail
 
-if [[ ! -z "$TOKEN" ]]; then
+if [[ -n "$TOKEN" ]]; then
 	GITHUB_TOKEN=$TOKEN
 fi
 
diff --git a/github-dev/release-email-notification b/github-dev/release-email-notification
index c749ecb..c39e55a 100755
--- a/github-dev/release-email-notification
+++ b/github-dev/release-email-notification
@@ -8,7 +8,7 @@ if [[ -z "$MAILGUN_API_KEY" ]]; then
 	exit 1
 fi
 
-if [[ ! -z "$MAILGUN_DOMAIN" ]]; then
+if [[ -n "$MAILGUN_DOMAIN" ]]; then
 	MAILGUN_DOMAIN_NAME=$MAILGUN_DOMAIN
 fi
 
diff --git a/github-dev/upload-assets b/github-dev/upload-assets
index b7936c9..854bf54 100755
--- a/github-dev/upload-assets
+++ b/github-dev/upload-assets
@@ -1,6 +1,6 @@
 #!/bin/bash
 
-if [[ ! -z "$TOKEN" ]]; then
+if [[ -n "$TOKEN" ]]; then
 	GITHUB_TOKEN=$TOKEN
 fi
 
diff --git a/mailgun/sendemail b/mailgun/sendemail
index ce1a28b..a1e2ba8 100755
--- a/mailgun/sendemail
+++ b/mailgun/sendemail
@@ -8,7 +8,7 @@ if [[ -z "$MAILGUN_API_KEY" ]]; then
 	exit 1
 fi
 
-if [[ ! -z "$MAILGUN_DOMAIN" ]]; then
+if [[ -n "$MAILGUN_DOMAIN" ]]; then
 	MAILGUN_DOMAIN_NAME=$MAILGUN_DOMAIN
 fi
 
diff --git a/mutt/entrypoint.sh b/mutt/entrypoint.sh
index 86ca55e..90a72ee 100755
--- a/mutt/entrypoint.sh
+++ b/mutt/entrypoint.sh
@@ -47,7 +47,7 @@ if [ -d "$HOME/.gnupg" ]; then
 		if [ -f "/usr/share/doc/mutt/examples/gpg.rc" ]; then
 			echo 'source /usr/share/doc/mutt/examples/gpg.rc'
 		fi
-		if [ ! -z "$GPG_ID" ]; then
+		if [ -n "$GPG_ID" ]; then
 			echo "set pgp_sign_as = $GPG_ID"
 		fi
 		echo 'set crypt_replysign=yes'
diff --git a/postfix/service/postfix/run b/postfix/service/postfix/run
index 97c0e92..6a73ecf 100755
--- a/postfix/service/postfix/run
+++ b/postfix/service/postfix/run
@@ -14,7 +14,7 @@ EOF
 # shellcheck disable=SC1091
 [ -f /etc/service/postfix/run.config ] && source /etc/service/postfix/run.config
 
-if [[ ! -z "$MAILNAME" ]]; then
+if [[ -n "$MAILNAME" ]]; then
 	echo "$MAILNAME" > /etc/mailname
 	postconf -e myorigin="/etc/mailname"
 
@@ -25,15 +25,15 @@ if [[ ! -z "$MAILNAME" ]]; then
 	EOF
 fi
 
-if [[ ! -z "$MY_NETWORKS" ]]; then
+if [[ -n "$MY_NETWORKS" ]]; then
 	postconf -e mynetworks="$MY_NETWORKS"
 fi
 
-if [[ ! -z "$MY_DESTINATION" ]]; then
+if [[ -n "$MY_DESTINATION" ]]; then
 	postconf -e mydestination="$MY_DESTINATION"
 fi
 
-if [[ ! -z "$ROOT_ALIAS" ]]; then
+if [[ -n "$ROOT_ALIAS" ]]; then
 	if [[ -f /etc/aliases ]]; then
 		sed -i '/^root:/d' /etc/aliases
 	fi
@@ -41,7 +41,7 @@ if [[ ! -z "$ROOT_ALIAS" ]]; then
 	newaliases
 fi
 
-if [[ ! -z "$RELAY" ]]; then
+if [[ -n "$RELAY" ]]; then
 	# setup the relay
 	cat >> /etc/postfix/main.cf <<- EOF
 	relayhost = $RELAY
@@ -52,7 +52,7 @@ if [[ ! -z "$RELAY" ]]; then
 	EOF
 fi
 
-if [[ ! -z "$TLS" ]]; then
+if [[ -n "$TLS" ]]; then
 	# setup tls
 	cat >> /etc/postfix/main.cf <<- EOF
 	smtp_use_tls = yes
@@ -60,7 +60,7 @@ if [[ ! -z "$TLS" ]]; then
 	EOF
 fi
 
-if [[ ! -z "$SASL_AUTH" ]]; then
+if [[ -n "$SASL_AUTH" ]]; then
 	cat >> /etc/postfix/main.cf <<- EOF
 	smtp_sasl_auth_enable = yes
 	smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd