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Re: Why does this only work when I am running a shellscript

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On 30/03/13 14:54, Barb Knox wrote:
> In article <8738vdmg0h.fsf@Servus.decebal.nl>,
>   Cecil Westerhof <Cecil@decebal.nl> wrote:
>> I have the following code:
>>      private static void doCommand(final String cmd) throws IOException {
>>          Process p;
>>          Scanner sc;
>>
>>          System.out.println("#" + cmd + "#");
>>          p  = Runtime.getRuntime().exec(cmd);
>>          sc = new Scanner(p.getInputStream());
>>          while (sc.hasNext()) {
>>              System.out.println(sc.nextLine());
>>          }
>>      }
>> When I use something like:
>>      /usr/bin/convert Š
>>
>> It hangs.
> I have not tested this, but I expect the Scanner is blocking waiting for
> input.  You might want to try  while (sc.hasNextLine()).

It's probably good advice anyway, but I don't think it makes much 
difference in this case. hasNext() tests for the next 'token', using a 
whitespace separator by default. This means that it will block while 
there are only blank lines on the unclosed input. The next non-blank 
line will unblock it, then each of the pending blank lines will be read, 
while hasNext() remains true (because the next token is still not 
consumed). Blank lines followed by EOF will be skipped, however.

I tested with the following program:

import java.io.*;
import java.util.*;

public class Scan {
     public static void main(String[] args) throws Exception {
         Scanner s = new Scanner(System.in);
         while (s.hasNext()) {
             String l = s.nextLine();
             System.out.printf("Next line: %s<--%n", l);
         }
     }
}

-- 
ss at comp dot lancs dot ac dot uk

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Why does this only work when I am running a shellscript Cecil Westerhof <Cecil@decebal.nl> - 2013-03-30 09:46 +0100
  Re: Why does this only work when I am running a shellscript Barb Knox <see@sig.below> - 2013-03-31 03:54 +1300
    Re: Why does this only work when I am running a shellscript Steven Simpson <ss@domain.invalid> - 2013-03-30 16:07 +0000
  Re: Why does this only work when I am running a shellscript markspace <markspace@nospam.nospam> - 2013-03-30 08:23 -0700
    Re: Why does this only work when I am running a shellscript Arne Vajhøj <arne@vajhoej.dk> - 2013-03-30 11:34 -0400
  Re: Why does this only work when I am running a shellscript Roedy Green <see_website@mindprod.com.invalid> - 2013-03-30 08:35 -0700
  Re: Why does this only work when I am running a shellscript RVic <rvince99@hotmail.com> - 2013-03-30 08:41 -0700
    Re: Why does this only work when I am running a shellscript Joerg Meier <joergmmeier@arcor.de> - 2013-03-31 01:00 +0100
    Re: Why does this only work when I am running a shellscript Roedy Green <see_website@mindprod.com.invalid> - 2013-03-31 17:04 -0700
  Re: Why does this only work when I am running a shellscript Steven Simpson <ss@domain.invalid> - 2013-03-30 16:13 +0000

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