diff --git a/rechnung.sh b/rechnung.sh
index dbd73a1..bb3f4ac 100755
--- a/rechnung.sh
+++ b/rechnung.sh
@@ -24,7 +24,7 @@ RUBBER_BIN=$(which rubber 2>/dev/null || echo "rubber")
 EXECUTABLES_TO_CHECK="$BC_BIN $TR_BIN $SED_BIN $CUT_BIN $TPUT_BIN $DATE_BIN $PDFLATEX_BIN $RUBBER_BIN"
 
 GENPDF=""
-if [ -x $RUBBER_BIN ]; then
+if [ -x "$RUBBER_BIN" ]; then
     GENPDF="$RUBBER_BIN -d "
 else
     GENPDF="$PDFLATEX_BIN -halt-on-error "
@@ -231,11 +231,11 @@ make_invoice() {
     echo -n "s!#POSITION#!" >>$SEDFILE; echo "$POSITION!" >>$SEDFILE
     echo -n "s!#BETRAG#!" >>$SEDFILE; echo "$BETRAG!" >>$SEDFILE
     echo -n "s!#DEADLINE#!" >>$SEDFILE; echo "$inv_dead!" >>$SEDFILE
-    cp $TEMPLATEFILE $filename
-    $SED_BIN -i -f $SEDFILE $filename
-    $GENPDF $filename
-    if [ -x $RUBBER_BIN ]; then
-	$RUBBER_BIN --clean $filename
+    cp "$TEMPLATEFILE" "$filename"
+    $SED_BIN -i -f "$SEDFILE" "$filename"
+    $GENPDF "$filename"
+    if [ -x "$RUBBER_BIN" ]; then
+	"$RUBBER_BIN" --clean "$filename"
     fi
 
     if [ $? -eq 0 ]; then
@@ -276,7 +276,7 @@ proced_ini_line() {
         is_option $line
         if [ $? -eq 0 ]
         then
-            set_value $line
+            set_value "$line"
         else
             print_warn "Invalid syntax: $line"
         fi
@@ -286,7 +286,7 @@ proced_ini_line() {
 quit() {
     printf "\n$BLUE"
     printf "[-] Exit$NORMAL\n"
-    exit $1
+    exit 1
 }
 
 
@@ -297,7 +297,7 @@ echo "= Rechnung v$PROGRAMM_VERSION ="
 echo "==================="
 
 # Verschiedene Basic Checks
-if [ -n $NUMBER_OF_COLORS ] && [ "$NUMBER_OF_COLORS" -ge 8 ]; then
+if [ -n "$NUMBER_OF_COLORS" ] && [ "$NUMBER_OF_COLORS" -ge 8 ]; then
     COLORED_OUTPUT=1
 fi
 
@@ -305,16 +305,16 @@ if [ $(id -u) -eq 0 ]; then
     echo "$0: Das Skript darf nicht als Root ausgeführt werden."
     exit 1
 fi
-check_binaries $EXECUTABLES_TO_CHECK
-check_readable $RECHNUNGSFILE
-check_readable $TEMPLATEFILE
+check_binaries "$EXECUTABLES_TO_CHECK"
+check_readable "$RECHNUNGSFILE"
+check_readable "$TEMPLATEFILE"
 printf "\n"
 
 # Kundendatei einlesen und rechnungen erstellen
 while IFS= read -r rawline
 do
-    trim_line $rawline
-    proced_ini_line $LINE_BUFFER
-done <$RECHNUNGSFILE
+    trim_line "$rawline"
+    proced_ini_line "$LINE_BUFFER"
+done < "$RECHNUNGSFILE"