diff --git a/nmap-parse-output b/nmap-parse-output
index 969dbf4..a48efe6 100755
--- a/nmap-parse-output
+++ b/nmap-parse-output
@@ -10,21 +10,25 @@ while [ -h "$SOURCE" ]; do # resolve $SOURCE until the file is no longer a symli
 done
 SCRIPT_DIR="$( cd -P "$( dirname "$SOURCE" )" && pwd )"
 
-XSLT_DIR=$SCRIPT_DIR/nmap-parse-output-xslt
+XSLT_DIR="$SCRIPT_DIR/nmap-parse-output-xslt"
 
 # functions (mostly for help)
 function xml_node_text() {
-  xmllint --xpath "//*[local-name()='$2' and namespace-uri()='http://xmlns.sven.to/npo']/text()" $1 2>/dev/null
+  # $1 = file, $2 = node
+  xmllint --xpath "//*[local-name()='$2' and namespace-uri()='http://xmlns.sven.to/npo']/text()" "$1" 2>/dev/null
 }
 
 function print_command_category() {
   echo "$1 Commands:"
-  for fullf in $XSLT_DIR/*.xslt; do
-    if [ "$(xml_node_text $fullf category)" == "$2" ]
+  for fullf in "$XSLT_DIR"/*.xslt; do
+    # If the glob didn't match any file, it will expand literally; skip in that case.
+    [ ! -f "$fullf" ] && continue
+
+    if [ "$(xml_node_text "$fullf" category)" == "$2" ]
     then
-      f=$(basename $fullf)
+      f=$(basename "$fullf")
       echo -e -n "  ${f%.*} "
-      xml_node_text $fullf comment || echo -e "\n\t(No documentation)"
+      xml_node_text "$fullf" comment || echo -e "\n\t(No documentation)"
     fi
   done
   echo 
@@ -56,8 +60,6 @@ UNFINISHED_SCAN=""
 
 while [ $# -gt 0 ]
 do
-  CURRENT_PARAM=$1
-
   case "$1" in
           --help|-h)
               help
@@ -76,14 +78,19 @@ done
 [ $# -lt 2 ] && help
 
 # check if input is readable
-NMAP_XML_OUTPUT=$1
-[ -f "$NMAP_XML_OUTPUT" -o "$NMAP_XML_OUTPUT" = "-" ] || { echo "Can't read nmap file: $NMAP_XML_OUTPUT.  Aborting." >&2; exit 1; }
+NMAP_XML_OUTPUT="$1"
+if [ -f "$NMAP_XML_OUTPUT" ] || [ "$NMAP_XML_OUTPUT" = "-" ]; then
+  :
+else
+  echo "Can't read nmap file: $NMAP_XML_OUTPUT.  Aborting." >&2
+  exit 1
+fi
 
-XSLT=$XSLT_DIR/$2.xslt
-[ -f $XSLT ] || { echo "Unknown command: $2.  Aborting." >&2; exit 1; }
+XSLT="$XSLT_DIR/$2.xslt"
+[ -f "$XSLT" ] || { echo "Unknown command: $2.  Aborting." >&2; exit 1; }
 
 # read post process command from xslt
-POST_PIPE=$(xml_node_text $XSLT post-processor)
+POST_PIPE=$(xml_node_text "$XSLT" post-processor)
 if [ -z "$POST_PIPE" ]
 then
   POST_PIPE="cat - "