Comment by brian_cloutier

> Ignoring include boilerplate and the like leaves us with roughly ten lines of code.

I'm not sure you get to claim a language is a scripting language and then ignore the boilerplate.

The equivalent python is 4 lines, just one more than the number of steps you're performing.

  import sys
  data = open(sys.argv[1]).readlines()
  lines = sorted(data)
  open(sys.argv[2], 'w').writelines(lines)

C++ is good at many things, but quickly creating readable scripts and live-coding with a REPL are not among them.