Added checks to make sure the specified track exists

Added precondition checks to validate input files and paths to return more informative error messages as per #2

node_modules/yargs/completion.sh.hbs

@@ -0,0 +1,28 @@
+###-begin-{{app_name}}-completions-###
+#
+# yargs command completion script
+#
+# Installation: {{app_path}} {{completion_command}} >> ~/.bashrc
+#    or {{app_path}} {{completion_command}} >> ~/.bash_profile on OSX.
+#
+_yargs_completions()
+{
+    local cur_word args type_list
+
+    cur_word="${COMP_WORDS[COMP_CWORD]}"
+    args=("${COMP_WORDS[@]}")
+
+    # ask yargs to generate completions.
+    type_list=$({{app_path}} --get-yargs-completions "${args[@]}")
+
+    COMPREPLY=( $(compgen -W "${type_list}" -- ${cur_word}) )
+
+    # if no match was found, fall back to filename completion
+    if [ ${#COMPREPLY[@]} -eq 0 ]; then
+      COMPREPLY=( $(compgen -f -- "${cur_word}" ) )
+    fi
+
+    return 0
+}
+complete -F _yargs_completions {{app_name}}
+###-end-{{app_name}}-completions-###