Proposal: Add Piping

[Alogani]

It should be a nice feature to have some sort of piping for conciseness, like in bash echo num | sed s/u/i/

Examples

Here is a working example/proof of concept

import asyncproc ## v0.4.2
import macros

macro `|`(a, b: typed): Future[string] =
    var newB = b.copyNimTree()
    let shSym = b[1]
    newB[1] = quote do:
        `shSym`.merge(input = some AsyncioBase(AsyncString.new(await `a`)))
    quote do:
        `newB`  

var sh = sh.merge(prefixCmd = some @["sh", "-c"], toRemove = { QuoteArgs })

proc main() {.async.} =
    echo await (sh.runGetOutput(@["echo", "'54\n'"]) |
        sh.runGetOutput(@["read a; echo a=$a'\n'"]) |
        sh.runGetOutput(@["read b; echo b=$b'\n'"]))

waitFor main()

Problematics

Here are some pain points before including it in the library

• Is | appropriate ?
  • Pros: concise, already used in shells.
  • Cons: not as readable as for example >
• runGetOutput ditch the line end. This is problematic for piping. Possible solutions :
  1. use run directly ?
     • Pros: concise
     • Cons: less explicit
  2. use RemoveLineEnd flag ?
     • Pros: explicit
     • Cons: behaviour of runGetOutput is not as reliable. Can be circumvet by decreting runGetOutput always ditch lineEnd no matter the flag. Or by saying internalCmd always ditch lineEnd. Or by using withoutLineEnd explicitly in shellcmd. Etc.
• The example syntax is verbose. How much could it be reduced without compromising flexibility and explicitness ?
• Should it accept a Future or the awaited result ? How could it play with implicitAsync ?
• {.async.} macro makes | macro be called two times (concerns all macros). But this is low priority