Can get stderr.

mypopen.c

#include <stdio.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/wait.h>
#include <malloc.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>

#ifdef __ANDROID__
#define	_PATH_BSHELL	"/system/bin/sh"
#define printf(fmt,args...)  ALOGW (fmt ,##args) 
#else 
#define	_PATH_BSHELL	"/bin/sh"
#endif


/*
 * Pointer to array allocated at run-time.
 */
static pid_t	*childpid = NULL;

/*
 * From our open_max(), {Prog openmax}.
 */
static int		maxfd;

FILE *
mypopen(const char *cmdstring, const char *type)
{
	int		i;
	int		pfd[2];
	pid_t	pid;
	FILE	*fp;

	/* only allow "r" "e" or "w" */
	if ((type[0] != 'r' && type[0] != 'w' && type[0] != 'e') || type[1] != 0) {
		errno = EINVAL;		/* required by POSIX */
		return(NULL);
	}

	if (childpid == NULL) {		/* first time through */
		/* allocate zeroed out array for child pids */
		maxfd = 256;
		if ((childpid = (pid_t*)calloc(maxfd, sizeof(pid_t))) == NULL)
			return(NULL);
	}

	if (pipe(pfd) < 0)
		return(NULL);	/* errno set by pipe() */

	if ((pid = fork()) < 0) {
		return(NULL);	/* errno set by fork() */
	} else if (pid == 0) {							/* child */
		if (*type == 'e') {
			close(pfd[0]);
			if (pfd[1] != STDERR_FILENO) {
				dup2(pfd[1], STDERR_FILENO);
				close(pfd[1]);
			}
		} else if (*type == 'r') {
			close(pfd[0]);
			if (pfd[1] != STDOUT_FILENO) {
				dup2(pfd[1], STDOUT_FILENO);
				close(pfd[1]);
			}
		} else {
			close(pfd[1]);
			if (pfd[0] != STDIN_FILENO) {
				dup2(pfd[0], STDIN_FILENO);
				close(pfd[0]);
			}
		}

		/* close all descriptors in childpid[] */
		for (i = 0; i < maxfd; i++)
			if (childpid[i] > 0)
				close(i);

		execl(_PATH_BSHELL, "sh", "-c", cmdstring, (char *)0);
		_exit(127);
	}

	/* parent continues... */
	if (*type == 'e') {
		close(pfd[1]);
		if ((fp = fdopen(pfd[0], "r")) == NULL)
			return(NULL);
	} else if (*type == 'r') {
		close(pfd[1]);
		if ((fp = fdopen(pfd[0], type)) == NULL)
			return(NULL);
	
	} else {
		close(pfd[0]);
		if ((fp = fdopen(pfd[1], type)) == NULL)
			return(NULL);
	}

	childpid[fileno(fp)] = pid;	/* remember child pid for this fd */
	return(fp);
}

int
mypclose(FILE *fp)
{
	int		fd, stat;
	pid_t	pid;

	if (childpid == NULL) {
		errno = EINVAL;
		return(-1);		/* popen() has never been called */
	}

	fd = fileno(fp);
	if ((pid = childpid[fd]) == 0) {
		errno = EINVAL;
		return(-1);		/* fp wasn't opened by popen() */
	}

	childpid[fd] = 0;
	if (fclose(fp) == EOF)
		return(-1);

	while (waitpid(pid, &stat, 0) < 0)
		if (errno != EINTR)
			return(-1);	/* error other than EINTR from waitpid() */

	return(stat);	/* return child's termination status */
}

int shellcmd(const char *cmd){
	FILE *fp;
	char buf[1024];
	fp = mypopen(cmd,"e");
	if (fp==NULL) return -1;

	while(fgets(buf,1024,fp)!=NULL)
	{
		printf("shellcmd:%s", buf);
	}

	pclose(fp);
	return 0;
}

int main()
{
	shellcmd("ls kangear");
}