reading standardInput ?

[K.-P. Kirchdoerfer]

If I understood it right, programs that can throw their output into a
pipe like ls or dir in fact write into standard input (e.g. ls -al |
grep). How can I read with NetRexx/Java from this pipe/standard
input?

TIA kp

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[Ed Tomlinson]

-----BEGIN PGP SIGNED MESSAGE-----

On Tue, 26 May 1998 21:45:15 +0100, K.-P. Kirchd”rfer wrote:

>If I understood it right, programs that can throw their output into a
>pipe like ls or dir in fact write into standard input (e.g. ls -al |
>grep). How can I read with NetRexx/Java from this pipe/standard
>input?

Here is a fragment from the njpipes command stage that show a way to
do this:
- --------------------------
method runCommand(a=rexx) private

   do
      r = Runtime.getRuntime
      p = r.exec(a)
   catch IOException
      exit(13)
   end

   in = PrintWriter(p.getOutputStream())
   do
      selectinput(1)
      loop forever
         in.println(String peekto())
         readto()
      end
   catch StageError
   finally
      in.close()
   end

   out  = BufferedReader(InputStreamReader(p.getInputStream()))
   do
      selectoutput(0)
   catch StageError
   end
   outputLines(out)

   err = BufferedReader(InputStreamReader(p.getErrorStream()))
   do
      selectoutput(1)
   catch StageError
   end
   outputLines(err)

   do
      p.waitfor()
- --    say p.exitValue()
      selectoutput(2)
      output(Rexx p.exitValue())
   catch StageError
      rc = rc()
   catch InterruptedException
      rc = 16
   end

   p.destroy()
- -----------------

Hope this helps,

Luck,
Ed Tomlinson ([hidden email])
Montreal, Canada

To obtain my public key mail me with a subject of: PGP Key


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[K.-P. Kirchdoerfer]

On Tue, 26 May 1998 18:00:11 -0500, Ed Tomlinson wrote:

>On Tue, 26 May 1998 21:45:15 +0100, K.-P. Kirchdörfer wrote:
>
>>If I understood it right, programs that can throw their output into a
>>pipe like ls or dir in fact write into standard input (e.g. ls -al |
>>grep). How can I read with NetRexx/Java from this pipe/standard
>>input?
>
>Here is a fragment from the njpipes command stage that show a way to
>do this:
>--------------------------
>method runCommand(a=rexx) private
>
>   do
>      r = Runtime.getRuntime
>      p = r.exec(a)
>   catch IOException
>      exit(13)
>   end
>
>   in = PrintWriter(p.getOutputStream())
>   do
>      selectinput(1)
>      loop forever
>         in.println(String peekto())
>         readto()
>      end
>   catch StageError
>   finally
>      in.close()
>   end

[...]

Thanks for that one; but what you are doing here is to create a
subprocess within your java class and then getting the I/O-streams of
the _subprocess_.

Your solution is a nice way to deal with outputstreams (standard and
error) of a native program started from a java program in the systems
runtime.

I was looking the systems standardinputstream - like in teh example -
ls | grep - e.g. I want to write grep.class (no, I won't do that) and
how can I catch the output of ls?

Well after looking into the java programmers faq, with some hints to
related problems and again reading the docs more carefully I found
java.lang.system with the var in, which has the output of e.g. ls
already, I just have to read it. Pretty simple, if one only find the
right way to do it.

regards kp
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[Mike Cowlishaw-2]

If reading it line-by-line is OK, try using the NetRexx special word ASK.  It
returns the next line from System.in.

Here's the codeit uses:

properties private static
  StdIn =BufferedReader(InputStreamReader(System.in))

/* <sgml> Function to return a line read from the standard input stream

[Martin Lafaix]

> From: "K.-P._Kirchdörfer" <[hidden email]>
> Well after looking into the java programmers faq, with some hints to
> related problems and again reading the docs more carefully I found
> java.lang.system with the var in, which has the output of e.g. ls
> already, I just have to read it. Pretty simple, if one only find the
> right way to do it.

Well, a simple solution is to use "ask".  The following code
implements a simple filter which displays lines containing a given
string:

  -- ngrep.nrx

  loop forever
    curline = ask
    if curline.pos(arg) > 0 then
      say curline
  catch NullPointerException
  end

You use it the following way:

  {0}[E:\LOCAL\nrx] dir | java ngrep "<DIR>"
  13/05/97  19:29      <DIR>           0  .
  13/05/97  19:29      <DIR>           0  ..
  18/01/98  21:57      <DIR>           0  ctr

[Catching NullPointerExceptions is not a recommended practice,
 but is here needed.]


Martin
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http://www.mygale.org/~lafaix

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[K.-P. Kirchdoerfer]

Thanks for all the input;
small question, but learned more than asked :)

>Well, a simple solution is to use "ask".  The following code
>implements a simple filter which displays lines containing a given
>string:

I wasn't shure, if the input will be line-oriented, therefor I used a
less readable and more java-like solution to read the input into a
2kb buffer and write to a file until all is done.

Both solutions, ask() and the one described, will do the work ('cause
the input in fact _is_ always line-oriented), I'm now wondering which
one would be faster.
This raises a more general question for me. I use whereever possible
NetRexx and a (net)rexxish style for programming, 'cause it's so
easy. Does this style have an impact on the performance? In the above
case, doing the job with ask() is simple. easy to understand, and
very few lines of code; doing it with a bufferedinputstream and
reading it into a buffer is less readable, and possibly introduces
bugs, 'cause it's more complicated, needs more lines of code..., but
will it run better without using the netrexx runtime?

regards kp

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