diff --git a/nyan b/nyan
index e344b70..58b1bfb 100755
--- a/nyan
+++ b/nyan
@@ -10,19 +10,19 @@ if [ ! -e "$(which pv)" ]; then
 fi
 
 function simplify_size_number {
-	declare -i bytes=$1
-	declare -i kilobytes=$((bytes/1024))
+	local declare -i bytes=$1
+	local declare -i kilobytes=$((bytes/1024))
 
-	size_str=""
+	local size_str=""
 
 	if [ $kilobytes -lt 1024 ]; then
 		size_str="${kilobytes}kb"
 	else
-		declare -i megabytes=$((kilobytes/1024))
+		local declare -i megabytes=$((kilobytes/1024))
 		if [ $megabytes -lt 1024 ]; then
 			size_str="${megabytes}mb"
 		else
-			declare -i gigabytes=$((megabytes/1024))
+			local declare -i gigabytes=$((megabytes/1024))
 			size_str="${gigabytes}gb"
 		fi
 	fi
@@ -33,10 +33,15 @@ while getopts ${optstring} args; do
 	case $args in
 		o) output_file=${OPTARG} ;;
 		:) echo "Output file required." ;;
+		# TODO: Expand this into something nicer looking.
 		h) echo "Usage: nyan -o [OUTPUT FILE] [INPUT FILE]..." && exit 0 ;;
 	esac
 done
 shift $((OPTIND-1))
+if [ -z "$output_file" ]; then
+	echo "Error: no output file specified."
+	exit 1
+fi
 
 echo "Concatenating files..."
 declare -i total_size=0
@@ -54,6 +59,8 @@ for fname in "$@"; do
 	fi
 done
 
+# TODO: Make sure that output_file does not exist. Maybe add an overwrite switch.
+
 if [ $abort -eq 0 ]; then
 	cat "$@" | pv -epts "$total_size" > "$output_file"
 	echo "Done!"