Re: Confused about how to use ``inputStream`` with ``osproc.startProcess``

[pmags]

Thank you, Vindaar. That's very helpful!

Re: Confused about how to use ``inputStream`` with ``osproc.startProcess``

[Vindaar]

Sorry, I didn't see the post before.

You're almost there. There's two small things missing in your code.

  1. you should add a newline to the string you write to the input stream. cat 
wants that newline
  2. instead of closing the input stream, you flush it.



Note however that with cat at least the output stream will never be "done". So 
you need some stopping criteria.


import osproc, streams

proc cat(strs: seq[string]): string =
  var command = "cat"
  var p = startProcess(command, options = {poUsePath})
  var inp = inputStream(p)
  var outp = outputStream(p)
  
  for str in strs:
# append a new line!
inp.write(str & "\n")
  
  # make sure to flush the stream!
  inp.flush()
  var line = ""
  var happy = 0
  while p.running:
if happy == strs.len:
  # with `cat` there will always theoretically be data coming from the 
stream, so
  # we have some artificial stopping criterium (maybe just Ctrl-C)
  break
elif outp.readLine(line):
  result.add(line & "\n")
inc happy
  close(p)

echo cat(@["hello", "world"])


Run

Re: Confused about how to use ``inputStream`` with ``osproc.startProcess``

[pmags]

Still hoping someone can offer some insight on the use of inputStream. Is the 
documentation simply wrong on this point?

Confused about how to use ``inputStream`` with ``osproc.startProcess``

[pmags]

I'm trying to understand how to effectively use `osproc.startProcess` with 
input and output streams. Using execProcess as an starting point, I've written 
a simple function which calls the unix `cat` program, passes strings of 
interest via an `inputStream` and reads from stdout using an `outputStream`.

The [inputStream 
documentation]([https://nim-lang.org/docs/osproc.html#inputStream%2CProcess](https://nim-lang.org/docs/osproc.html#inputStream%2CProcess))
 specifically warns: "WARNING: The returned Stream should not be closed 
manually as it is closed when closing the Process p." However if I don't close 
the inputStream manually as shown in the code below the thread is blocked and 
never returns.

Can someone offer some insight into how I'm supposed to pass data to an 
inputStream w/out closing it manually? Thanks!


import osproc, streams

proc cat(strs: seq[string]): string =
  var command = "cat"
  var p = startProcess(command, options = {poUsePath})
  var inp = inputStream(p)
  var outp = outputStream(p)
  
  for str in strs:
inp.write(str)
  
  close(inp) # this line is needed or the thread blocks
  
  var line = ""
  while true:
if outp.readLine(line):
  result.add(line)
  result.add("\n")
elif not running(p): break
  close(p)

echo cat(@["hello", "world"])


Run