diff --git a/nyan b/nyan
index 697a960..ca6a11f 100755
--- a/nyan
+++ b/nyan
@@ -1,6 +1,8 @@
 #!/bin/bash
 optstring="o:"
-input_files=""
+declare -i abort=0
+
+# TODO: Check for dependencies pv and stat.
 
 while getopts ${optstring} args; do
 	case $args in
@@ -8,20 +10,28 @@ while getopts ${optstring} args; do
 		:) echo "Output file required." ;;
 	esac
 done
-
 shift $((OPTIND-1))
-echo $output_file
-
 
 echo "Concatenating files..."
 declare -i total_size=0
 for fname in "$@"; do
-	#TODO: Make sure this file exists and isn't a directory!
-	current_file_size=$(stat -c%s "$fname")
-	let total_size=$total_size+$current_file_size
-	echo "${fname} is ${total_size}b and valid."
+	if [ ! -e "$fname" ]; then
+		abort=1
+		echo "${fname} does not exist."
+	elif [ -d "$fname" ]; then
+		abort=1
+		echo "${fname} is a directory."
+	else
+		current_file_size=$(stat -c%s "$fname")
+		total_size=$((total_size+current_file_size))
+		# TODO: Use something more legible than bytes.
+		echo "Adding ${fname} at ${total_size}b."
+	fi
 done
 
-cat "$@" | pv -epts "$total_size" > "$output_file"
-
-echo "Done!"
+if [ $abort -eq 0 ]; then
+	cat "$@" | pv -epts "$total_size" > "$output_file"
+	echo "Done!"
+else
+	echo "Errors occurred, concatenation aborted."
+fi