diff --git a/jsawk b/jsawk
index bb02531..4b2f4e1 100755
--- a/jsawk
+++ b/jsawk
@@ -12,10 +12,13 @@
 #   licenses of the incorporated software below.
 #
 
-TMP1=`mktemp /tmp/tmp.XXXXXX`
-TMP2=`mktemp /tmp/tmp.XXXXXX`
+TMP1=$(mktemp /tmp/tmp.XXXXXX)
+TMP2=$(mktemp /tmp/tmp.XXXXXX)
 
-trap "rm -f $TMP1 $TMP2" SIGINT SIGTERM SIGHUP SIGQUIT
+cleanup() {
+  rm -f $TMP1 $TMP2
+}
+trap cleanup SIGINT SIGTERM SIGHUP SIGQUIT
 
 cat <<'__END__' > $TMP1
 
@@ -1286,10 +1289,10 @@ while getopts :hni:s:j:q:f:b:a:v: opt; do
 done
 
 if [ $get_lines != "no" ]; then
-  if [ -n "$input_string" ]; then
+  if [ "$input_string" ]; then
   	# Pass in the input string specified directly
   	echo "$input_string" > $TMP2
-  elif [ -n "$input_file" ]; then
+  elif [ "$input_file" ]; then
   	# Pass in the input file contents specified, first checking the file exists
   	if ! [ -e "$input_file" ]; then
   		echo "Error: Input file cannot be found: $input_file"
@@ -1298,7 +1301,7 @@ if [ $get_lines != "no" ]; then
   	cat "$input_file" > $TMP2
   else
   	# Read input from STDIN
-    echo "$(cat 2>/dev/null)" > $TMP2
+    cat 2>/dev/null > $TMP2
   fi
   nlines=$(grep -c '$' $TMP2 2>/dev/null || echo 0)
 fi
@@ -1318,9 +1321,9 @@ res=$(cat $TMP2 2>/dev/null | $JSBIN $TMP1 $nlines "$@")
 out=$(echo "$res" |sed '/^OUT: /s/^.....//p;d')
 err=$(echo "$res" |sed '/^ERR: /s/^.....//p;d')
 
-[ -n "$err" ] && echo "$err" 1>&2
-[ -n "$out" ] && echo "$out"
+[ "$err" ] && echo "$err" 1>&2
+[ "$out" ] && echo "$out"
 
-rm -f $TMP1 $TMP2
+cleanup
 
 exit $ret