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From: mroz@eplrx7.uucp (Peter Mroz)
Newsgroups: comp.unix.aix
Subject: Problems with popen on RS/6000
Keywords: popen, C, vmstat
Message-ID: <1990Aug15.203239.8832@eplrx7.uucp>
Date: 15 Aug 90 20:32:39 GMT
Sender: usenet@ee.udel.edu
Organization: DuPont Engineering Physics Lab
Lines: 56
Nntp-Posting-Host: louie.udel.edu

I'm having a problem with popen sending back buffered output.  I am in the
process of writing a program to display vmstat output using curses.  However,
when I issue the command

	vin = popen("vmstat 2","r");

I can't read anything with fgets until some internal buffer is filled.  I
tried running the same program on a Sun and it works just fine.  Any suggestions
would be appreciated.

On the IBM RS/6000 the following program doesn't send back any vmstat output
until 30 seconds have passed.  On the Sun it sends output back every second,
like I thought it would.

/* testp.c */
#include <stdio.h>
#include <signal.h>

char *progname;		/* program name for error messages */

main (argc, argv)
	int argc;
	char *argv[];
{

	FILE *vin, *popen();
	char *vmstat_cmd = "vmstat 1 30";
	char input_line[BUFSIZ];

	progname = argv[0];
	if ((vin = popen(vmstat_cmd, "r")) == NULL)
	{
		fprintf(stderr, "%s: can't run %s\n", progname, vmstat_cmd);
		exit(1);
	}

	printf("\nOK.  Pipe initialized \n");

	fgets(input_line, sizeof input_line, vin);
	printf("%s", input_line);

	while (fgets(input_line, sizeof input_line, vin) != NULL)
	{
		printf("%s", input_line);
	}
}



-- 
    Peter Mroz                    |    E.I. Du Pont de Nemours & Co.
    eplrx7!mroz@uunet.uu.net      |    Consultant, Scicon
    mrozpa%wmvx@dupont.com        |    DuPont Building, D4078
                                  |    Wilmington, DE 19898
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