glibc/manual/examples/popen.c

/* Pipe to a Subprocess
   Copyright (C) 1991-2019 Free Software Foundation, Inc.

   This program is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License
   as published by the Free Software Foundation; either version 2
   of the License, or (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, see <http://www.gnu.org/licenses/>.
*/

#include <stdio.h>
#include <stdlib.h>

void
write_data (FILE * stream)
{
  int i;
  for (i = 0; i < 100; i++)
    fprintf (stream, "%d\n", i);
  if (ferror (stream))
    {
      fprintf (stderr, "Output to stream failed.\n");
      exit (EXIT_FAILURE);
    }
}

/*@group*/
int
main (void)
{
  FILE *output;

  output = popen ("more", "w");
  if (!output)
    {
      fprintf (stderr,
	       "incorrect parameters or too many files.\n");
      return EXIT_FAILURE;
    }
  write_data (output);
  if (pclose (output) != 0)
    {
      fprintf (stderr,
	       "Could not run more or other error.\n");
    }
  return EXIT_SUCCESS;
}
/*@end group*/