From:	"Mark E." <snowball3 AT bigfoot DOT com>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Gnu compiler for Perl
Date:	Thu, 14 Jun 2001 14:05:21 -0400
Organization:	Snowball's Web
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References:	<20010614145506 DOT EFE4 DOT H DOT M DOT BRAND AT hccnet DOT nl> <Pine DOT SUN DOT 3 DOT 91 DOT 1010614160710 DOT 6496A AT is> <20010614160042 DOT EFE9 DOT H DOT M DOT BRAND AT hccnet DOT nl> <2110-Thu14Jun2001190959+0300-eliz AT is DOT elta DOT co DOT il>
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"Eli Zaretskii" <eliz AT is DOT elta DOT co DOT il> wrote:

>Mark, could you please see what does Bash do with "> /dev/null" that
>it doesn't do with ">> /dev/null"?

This program simulates (if I did it right) what Bash does with 'echo x > /dev/null'
and 'echo x >> /dev/null'. I put in calls to 'perror' to show at what point the
program fails (if anywhere). This works under win98. Try it under w2k and report the
results. If this works, try modifying the example to run a program instead of
printing a message.

#include <unistd.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <stdio.h>
#include <errno.h>

/* Simulate the script:
   echo "abc" > /dev/null
   echo "abc" >> /dev/null
*/

int main()
{
  int fd1, fd2, ret;

  fd1 = dup(1);

  /* open /dev/null */
  fd2 = open("/dev/null", O_WRONLY | O_TRUNC | O_CREAT, S_IWUSR);

  if (fd2 < 0)
  {
    perror("#1");
    return 1;
  }

  if (dup2(fd2, 1) < 0)
  {
    perror("#2");
    return 1;
  }

  /* echo "abc" > /dev/null */
  printf("abc");
  putchar('\n');
  fflush (stdout);

  if (dup2(fd1, 1) < 0)
  {
    perror("#3");
    return 1;
  }

  close(fd2);

  /* echo "abc" >> /dev/null */
  fd2 = open("/dev/null", O_WRONLY | O_APPEND | O_CREAT, S_IWUSR);

  if (fd2 < 0)
  {
    perror("#4");
    return 1;
  }

  if (dup2(fd2, 1) < 0)
  {
    perror("#5");
    return 1;
  }

  printf("abc");
  putchar('\n');
  fflush (stdout);

  if (dup2(fd1, 1) < 0)
  {
    perror("#6");
    return 1;
  }

  /* close up shop */
  close (fd2);
  close (fd1);

  printf("Success!\n");
  return 0;
}

-- 
Mark E.: snowball3 AT bigfoot DOT com
http://snowball.frogspace.net/

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