diff --git a/completions/docker-compose.completion.sh b/completions/docker-compose.completion.sh
index be58a51..b3fabd8 100644
--- a/completions/docker-compose.completion.sh
+++ b/completions/docker-compose.completion.sh
@@ -552,7 +552,7 @@ _docker_compose() {
 	done
 
 	local completions_func=_docker_compose_${command//-/_}
-	_omb_util_function_exists $completions_func && $completions_func
+	_omb_util_function_exists "$completions_func" && "$completions_func"
 
 	eval "$previous_extglob_setting"
 	return 0
diff --git a/completions/docker-machine.completion.sh b/completions/docker-machine.completion.sh
index 5009864..c6d0a39 100644
--- a/completions/docker-machine.completion.sh
+++ b/completions/docker-machine.completion.sh
@@ -244,7 +244,7 @@ _docker_machine() {
 
     local completion_func=_docker_machine_"${command//-/_}"
     if _omb_util_function_exists "${completion_func}"; then
-        ${completion_func}
+        "${completion_func}"
     fi
 
     return 0
diff --git a/completions/docker.completion.sh b/completions/docker.completion.sh
index c14c600..6b3d8c1 100644
--- a/completions/docker.completion.sh
+++ b/completions/docker.completion.sh
@@ -394,7 +394,7 @@ __docker_subcommands() {
 				subcommand_pos=$counter
 				local subcommand=${words[$counter]}
 				local completions_func=_docker_${command}_${subcommand}
-				_omb_util_function_exists $completions_func && $completions_func
+				_omb_util_function_exists "$completions_func" && "$completions_func"
 				return 0
 				;;
 		esac
@@ -2953,7 +2953,7 @@ _docker() {
 	fi
 
 	local completions_func=_docker_${command}
-	_omb_util_function_exists $completions_func && $completions_func
+	_omb_util_function_exists "$completions_func" && "$completions_func"
 
 	eval "$previous_extglob_setting"
 	return 0
diff --git a/completions/maven.completion.sh b/completions/maven.completion.sh
index 94aaf1d..a5d36c6 100644
--- a/completions/maven.completion.sh
+++ b/completions/maven.completion.sh
@@ -6,8 +6,8 @@
 
 function_exists()
 {
-	_omb_util_function_exists $1
-	return $?
+	_omb_util_function_exists "$1"
+	return "$?"
 }
 
 function_exists _get_comp_words_by_ref ||
diff --git a/completions/packer.completion.sh b/completions/packer.completion.sh
index 22369e2..d2ac8e0 100644
--- a/completions/packer.completion.sh
+++ b/completions/packer.completion.sh
@@ -133,7 +133,7 @@ _packer_completion ()
     _omb_util_function_exists _get_comp_words_by_ref && _get_comp_words_by_ref -n = cur
 
     COMPREPLY=()
-    local i c=1 command
+    local i c=1 command=
 
     while [ $c -lt $COMP_CWORD ]; do
         i="${COMP_WORDS[c]}"
@@ -144,7 +144,7 @@ _packer_completion ()
         ((c++))
     done
 
-    if [ -z $command ]; then
+    if [ -z "$command" ]; then
         case "$cur" in
             '-'*)
                 __packercomp "-machine-readable --help --version"
@@ -157,7 +157,7 @@ _packer_completion ()
     fi
 
     local completion_func="__packer_${command}"
-    _omb_util_function_exists $completion_func && $completion_func
+    _omb_util_function_exists "$completion_func" && "$completion_func"
 }
 
 complete -o nospace -F _packer_completion packer