Total Number of Lines of a Given File Type in a Folder

getTotalLineCount.sh

#!/bin/bash

if [ -z "$1" ] # Check if no argument was passed
then
    echo "No extension specified."
    exit
fi

# If someone passes * as an argument it'll pass all the
# files in the directory as arguments, so we just need
# check if another variable is set and we'll know
# whether more than one argument was passed
if [ "$2" ]
then
    find . -name '*.*' | xargs wc -l
else
    find . -name '*.'$1 | xargs wc -l
fi