diff --git a/install.sh b/install.sh
index 9d52695..db544d2 100755
--- a/install.sh
+++ b/install.sh
@@ -1,4 +1,5 @@
 #!/bin/bash
+# shellcheck disable=SC1090 # dynamically sourced file
 
 SEQGITURL="https://winklerfamilie.eu/git/efelon/shell_sequencer.git"
 DEFAULT_DIR="/opt/sequencer"
@@ -14,7 +15,7 @@ SEQUENCER_DIR="$1"
 if [ -z "$SEQUENCER_DIR" ]; then
   [ -w "$(dirname "$DEFAULT_DIR")" ] && SEQUENCER_DIR="$DEFAULT_DIR"
   # Fallback to working directory
-  [ -z "$SEQUENCER_DIR" ] && $SEQUENCER_DIR="${WDIR}/sequencer"
+  [ -z "$SEQUENCER_DIR" ] && SEQUENCER_DIR="${WDIR}/sequencer"
 fi
 
 # Check if already installed
@@ -23,36 +24,34 @@ if [ -d "$SEQUENCER_DIR" ]; then
   echo "     $SEQUENCER_DIR"
   exit 1
 fi
-if [ ! -w "$(dirname $SEQUENCER_DIR)" ]; then
-  echo " [E] Your user has no permission to write to $(dirname $SEQUENCER_DIR)"
+if [ ! -w "$(dirname "$SEQUENCER_DIR")" ]; then
+  echo " [E] Your user has no permission to write to $(dirname "$SEQUENCER_DIR")"
   exit 2
 fi
 
 # Install git if neccessary
-which git >>/dev/null 2>&1
-if [ $? != 0 ]; then
+if ! which git >>/dev/null 2>&1; then
   echo " [W] Git not found and will be installed"
-  apt update 
-  if [ $? != 0 ]; then
+  
+  if ! apt update; then
     echo " [W] Cannot update apt repositories"
   fi
-  apt install git -y
-  if [ $? != 0 ]; then
+  
+  if ! apt install git -y; then
     echo " [E] Cannot install git via apt"
     exit 3
   fi
 fi
 
 # Clone sequncer to target directory
-git clone $SEQGITURL "$SEQUENCER_DIR"
-if [ $? -ne 0 ]; then
+if ! git clone $SEQGITURL "$SEQUENCER_DIR"; then
   echo " [E] Error cloning git repository:"
   echo "     $SEQGITURL"
   exit 4
 fi
 
 # If available use configuration
-. ${SEQUENCER_DIR}/sequencer.cfg >/dev/null 2>&1
+. "${SEQUENCER_DIR}/sequencer.cfg" >/dev/null 2>&1
 
 # Set to default if not configured
 [ -z "$SEQUENCER_USER_SEQS" ] && SEQUENCER_USER_SEQS="$DEFAULT_USER_SEQS"
diff --git a/installCompletion.sh b/installCompletion.sh
index b1c0dbb..14dc8cb 100755
--- a/installCompletion.sh
+++ b/installCompletion.sh
@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 # Get script working directory
 sq_dir="$(cd "$(dirname -- "$(realpath "${BASH_SOURCE[0]}")")" >>/dev/null 2>&1 && pwd)"
@@ -8,14 +8,14 @@ _sequencerCompletion() {
   local SEQCOMP_LOADER="$HOME/.bashrc"
   local SEQCOMP_SOURCE=". \"$SEQCOMP_LOC\""
 
-  grep "$SEQCOMP_SOURCE" "$SEQCOMP_LOADER" >>/dev/null 2>&1
-  if [ $? -eq 0 ]; then
+  if grep "$SEQCOMP_SOURCE" "$SEQCOMP_LOADER" >>/dev/null 2>&1; then
     echo " [I] Completion already installed ($SEQCOMP_LOADER)"
   else
     echo "$SEQCOMP_SOURCE" >>"$SEQCOMP_LOADER"
-    [ $? -eq 0 ] && echo " [I] Sequence bash-completion installed"
+    echo " [I] Sequence bash-completion installed"
   fi
-  source "$SEQCOMP_LOC"
+  # shellcheck source=sqn-completion.bash
+  . "$SEQCOMP_LOC"
 }
 
 _sequencerCompletion