docs: def env_to_statement(env):
      ''' Return the abstraction description of an environment variable definition
      into a statement for shell script.
  
      >>> env_to_statement(dict(name='X', value='Y'))
      'X="Y"; export X'
      >>> env_to_statement(dict(name='X', value='Y', raw=True))
      'X=Y; export X'
      >>> env_to_statement(dict(name='X', value='"A","B","C"'))
      'X="\\\\"A\\\\",\\\\"B\\\\",\\\\"C\\\\""; export X'
      >>> env_to_statement(dict(file="Y"))
      '. "Y"'
      >>> env_to_statement(dict(file="'RAW $FILE'", raw=True))
      ". 'RAW $FILE'"
      >>> # Source file takes precedence
      >>> env_to_statement(dict(name='X', value='"A","B","C"', file="S"))
      '. "S"'
      >>> env_to_statement(dict(execute="module load java/1.5.1"))
      'module load java/1.5.1'
      '''
      source_file = env.get('file', None)
      if source_file:
          return '. %s' % __escape(source_file, env)
      execute = env.get('execute', None)
      if execute:
          return execute
      name = env['name']
      value = __escape(env['value'], env)
      return '%s=%s; export %s' % (name, value, name)