diff --git a/libexec/portzap/git-changed-files b/libexec/portzap/git-changed-files
index afbc658..f00bec5 100644
--- a/libexec/portzap/git-changed-files
+++ b/libexec/portzap/git-changed-files
@@ -7,8 +7,8 @@ commit=$2
 
 ##
 # main
-cd ${gitdir}
-add=$(git diff --name-only --diff-filter=A ${commit} HEAD)
-mod=$(git diff --name-only --diff-filter=M ${commit} HEAD)
-echo ${add}
-echo ${mod}
+cd "${gitdir}"
+add=$(git diff --name-only --diff-filter=A "${commit}" HEAD)
+mod=$(git diff --name-only --diff-filter=M "${commit}" HEAD)
+echo "${add}"
+echo "${mod}"
diff --git a/libexec/portzap/git-removed-files b/libexec/portzap/git-removed-files
index 48219c1..1190ebb 100644
--- a/libexec/portzap/git-removed-files
+++ b/libexec/portzap/git-removed-files
@@ -7,5 +7,5 @@ commit=$2
 
 ##
 # main
-cd ${gitdir}
-git diff --name-only --diff-filter=D ${commit} HEAD
+cd "${gitdir}"
+git diff --name-only --diff-filter=D "${commit}" HEAD
diff --git a/libexec/portzap/git-rev b/libexec/portzap/git-rev
index a5cf25a..4f94ab8 100644
--- a/libexec/portzap/git-rev
+++ b/libexec/portzap/git-rev
@@ -6,5 +6,5 @@ gitdir=$1
 
 ##
 # main
-cd ${gitdir}
+cd "${gitdir}"
 git rev-parse HEAD
diff --git a/libexec/portzap/portzap-install b/libexec/portzap/portzap-install
index 06f4990..baff225 100755
--- a/libexec/portzap/portzap-install
+++ b/libexec/portzap/portzap-install
@@ -23,8 +23,8 @@ perform_update()
     for file in ${add}; do
         target="${installdir}/${file}"
         parent=$(dirname "${target}")
-        if [ ! -e ${parent} ]; then
-            mkdir -p ${parent}
+        if [ ! -e "${parent}" ]; then
+            mkdir -p "${parent}"
         fi
         cp "${file}" "${target}"
         chown root:_portzap "${target}"
@@ -39,7 +39,7 @@ perform_install()
         -exec cp -Rfv {} "${installdir}" \; \
         -exec chown -R root:_portzap "${installdir}/{}" \;
     for path in ${artifacts}; do
-        rm -rf "${installdir}/${path}"
+        rm -rf "${installdir:?}/${path}"
     done
 }
 
@@ -52,4 +52,4 @@ if [ -e "${revfile}" ]; then
 else
     perform_install
 fi
-echo $(doas -u _portzap ${libexec}/git-rev ${gitdir}) > ${revfile}
+doas -u _portzap ${libexec}/git-rev "${gitdir}" > "${revfile}"
diff --git a/libexec/portzap/portzap-setup b/libexec/portzap/portzap-setup
index b453d01..04b6516 100755
--- a/libexec/portzap/portzap-setup
+++ b/libexec/portzap/portzap-setup
@@ -16,7 +16,7 @@ if ! id -u _portzap > /dev/null 2>&1; then
 echo "[ok] add _portzap user, group and home directory"
 fi
 
-if ! fgrep "${conf}" "${doas}" > /dev/null 2>&1; then
+if ! grep -F "${conf}" "${doas}" > /dev/null 2>&1; then
     echo "${conf}" >> "${doas}"
     echo "[ok] update ${doas}"
 fi