advanced functions for process / subprocess management

[refaktor]

From the lobste.rs thread:

As for subprocess management: The simple cases are: start a process, synchronously or asynchronously, but sync might suffice, if you can start a process in a go-routine. Be able to catch it's output or redirect it. Be able to merge the output streams (and redirect the merged stream), be able to provide input. So far for the basics. Then it gets harder: start a process asynchronously and be able to read out the streams while it runs, and to provide input base on the outputs. Most subporcessing libraries only offer the possibility to set the data that should be sent to stdin before the process is started, but not after starting it. Additionally, if you could do simple call chains like ls -la | wc -l and then catch the last output, that would be very nice too.

reference: https://lobste.rs/s/vw12iy/when_if_is_just_function#c_eyoih5

[refaktor]

@lluchs made great progress towards this in a PR mentioned above. Feedback and further ideas are welcome.

//cc: @KnorrFG

[refaktor]

@lluchs I renamed cmd and cmd\capture to scmd and scmd\capture because I still need it for some my utils. Like the music player :)

(scmd simple cmd or string cmd). If your functions will cover these cases we will remove them.

[lluchs]

Overview of what I have implemented so far and what is still missing:

• start a synchronous process
• start an asynchronous process
  • Not sure whether we want this - using goroutines for asynchronous processes might be nicer.
• catch output
• redirect output
• merge output streams
• redirect merged stream
  • No special support, but redirecting stdout and stderr to the same target would probably work.
• provide input
• read or write streams while the process is running
  • While it's possible to pass readers or writers to stdout/stdin, you can't interact much with these readers and writers. This will need some supporting work around general I/O functions.
• simple call chains

[refaktor]

Thank you, awesome! (related: #670 (comment))

start an asynchronous process
Not sure whether we want this - using goroutines for asynchronous processes might be nicer.

I don't have it in my mind concretely, but sometimes I imagine I would like to start a process, get the PID and forget about it, or just send it a signal later.

For example I have an third party server and I would like to manage it with Go. Maybe even store the PID, detach / Release the process and exit Go script and use that PID at next evocation of script. I think there is cmd.Start and Release function in Go.

redirect merged stream

read or write streams while the process is running

I don't have much experience with this so you be the judge.

btw: I thought about it and I'm adding a flagword to Rye. It will have optional short and long form. For example "-v" and "--verbose" could both be the same flag word. For now it will be used only for DSL-s, as I feel it would over diversify the language if we also use that (but there is one set of problems where it might be useful, we will see). I will have a PR for this today I hope. (related: https://www.reddit.com/r/ryelang/comments/1opusig/new_dsl_for_working_with_external_processes_cmd_sh/)

[refaktor]

PR from @lluchs was merged today. More information on: #670

I think this is an excellent start, and more than start, to provide this. We will improve it and extend it with further practical use, so further suggestions and issues are welcome.