#!/usr/bin/env python

 # long version of this one liner: python -c 'import yaml,sys;yaml.safe_load(sys.stdin)' < yamltest.txt
 import yaml
 import sys
 
 if len(sys.argv) > 1:
     check_file = open(sys.argv[1])
 else:
     check_file = sys.stdin
 
 try:
     yaml.safe_load(check_file)
 except yaml.scanner.ScannerError as e:
     sys.exit('Invalid YAML:\n%s' % str(e))
 
 print('valid YAML')