#include <stdio.h> /* fprintf(3), perror(3), stderr */
#if !defined EX_OSERR || !defined EX_USAGE
#	include <sysexits.h>
#endif
#include <unistd.h> /* dup2(2), fork(2), pipe(2), STDERR_FILENO,
                     * STDOUT_FILENO */
#include <sys/types.h> /* <sys/wait.h> */
#include <sys/wait.h> /* waitpid(2), WEXITSTATUS */
#include "libpsargs.h" /* check_arg(3), corresponding_arg(3) */

int oserr(char *s){

	perror(s);

	return EX_OSERR;
}
int main(int argc, char *argv[]){
	int child;
	char **corr;
	char **curr;
	int e[2];
	int efd;
	int i;
	int o[2];
	int ofd;
	int pid;

	if(argc < 2 || check_arg(curr = &argv[1]) != 3){
		fprintf(stderr,
			"Usage: %s \"[\" [command] (arguments...) \"]\""
			"\t"	"\"[\" [command] (arguments...) \"]\""
			" \"[\" [command (arguments...) \"]\"\n",
			argc == 0 ? "<no argv[0]>" : argv[0]);
		return EX_USAGE;
	}

	if(		(ofd = dup(STDOUT_FILENO)) < 0 /* preserve stdout */
			|| (efd = dup(STDERR_FILENO)) < 0 /* and stderr */
			|| pipe(o) < 0 /* establish out pipe */
			|| pipe(e) < 0 /* and err pipe, and use them: */
			|| dup2(o[1], STDOUT_FILENO) != STDOUT_FILENO
			|| dup2(e[1], STDERR_FILENO) != STDERR_FILENO)
		return oserr(argv[0]);

	/* start the source command first because it's the most critical point
	 * of failure */
	*(corr = corresponding_arg(curr++)) = NULL;
	switch(pid = fork()){
		case  0:	execvp(curr[0], curr);
		case -1:	return oserr(argv[0]);
	}

	/* restore preserved stdout/stderr */
	if(		dup2(ofd, STDOUT_FILENO) != STDOUT_FILENO
			|| dup2(efd, STDERR_FILENO) != STDERR_FILENO)
		return oserr(argv[0]);

	for(i = 1; i <= 2; ++i){
		curr = corr + 1;
		*(corr = corresponding_arg(curr++)) = NULL;
		if(dup2(((i == 1) ? o : e)[0], STDIN_FILENO != STDIN_FILENO))
			return oserr(argv[0]);
		switch(fork()){
		case  0:	execvp(curr[0], curr);
		case -1:	return oserr(argv[0]);
 		}
	}

	waitpid(pid, &child, 0);

	return WEXITSTATUS(child);
}