minor REPL enhancements

[michaelficarra]

Full list of changes in line number order:

• trailing whitespace
• a trapped SIGINT causes suppressed terminal output after REPL "exits" (should fix Ctrl+C from REBL messes up shell; Ctrl+D works fine #151)
  • submitted related issue REPL: piped input causes infinite loop #234
• formatting
• more formatting
• when piping to the REPL, it's nice to have it echoed to $stdout
• don't save commented lines to the history
• exit with a successful error code

[jhellerstein]

what's the intention here?

[jhellerstein]

Ah, I see from your comment you want output when it's used in a pipe. I personally think this should be off by default, but it's a nice command-line option. For Postgres' psql it's the "-a" option, for example.

[michaelficarra]

Yeah, it's a nice REPL feature. I don't see why a flag would be useful, though. Is there a reason someone wouldn't want the output?

[jhellerstein]

Well, if you're writing a pipe it's not necessarily nice to have things in the middle dumping stuff to stdout. As another example, there's tar -v. I'm old (from when cp was braindead) so I often run things like "tar cf - . | (cd /foo/bar; tar xf -)". I definitely don't want both of the tar calls to dump the file list, and in many cases I don't want either one to do so. But I agree that it's a useful flag.

[michaelficarra]

But who's using REPL output as the input to a pipe? Again, I don't think there's a use case that would prefer the input not to be echoed, so no need for a flag. At least not one that's off by default.

[jhellerstein]

It's not clear to me that you always (or usually) want to see rebl input lines on stdout any more than you'd want to see inbound network messages on stdout. If your goal is to control bud from a command line script and see what it does, it's not clear whether you want that control logic in the output.

Anyway, I'm very open to a command-line flag on this; we can ponder what the right default is but the important thing is to enable what you're asking for here.