example for redirecting stderr,stdout in seperate files using two way pipes concept
 

Please give example or suggestions for redirecting stderr , stdout in separate files using two way pipes concept.

I did the following example , but I am getting crashes after running some time.
I write following program for redirecting stderr , stdout in separate files while running script remotly on another linux system using plink.
Here out put is redirecting to outputfile and err is redirecting to errfile.Here I should wait the process upto comlpeting the total script execution.




int main(){
int pid=0;
int write_stdin[2], read_stdout[2];

pipe(write_stdin);
pipe(read_stdout);

/* Fork the process */
pid = fork();

switch (pid) {
case 0: /* Child process */
close(write_stdin[1]);
close(read_stdout[0]);

/* Replace stdin and stdout with the new fds */
dup2(write_stdin[0], STDIN_FILENO);
dup2(read_stdout[1], STDOUT_FILENO);

close(write_stdin[0]);
close(read_stdout[1]);
int f,ferr;
f=creat(outputFilename, S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH));
ferr=creat(errFileName, S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH);

dup2(f,STDOUT_FILENO);
dup2(ferr, STDERR_FILENO);
close(f); // original not needed after dup2
close(ferr); // original not needed after dup2
execvp(exeName,argv);
_exit(0);
break;

case -1: /* fork() error */
printf("Fork() error for host");
return NULL;
break;

default: /* Parent process */
/* Close unneeded fds */
close(write_stdin[0]);
close(read_stdout[1]);
struct pollfd waitfordata[1];
waitfordata[0].fd=read_stdout[0];
waitfordata[0].events=POLLIN;
sleep(1);

//run the commands
talkToPlink(waitfordata,read_stdout[0],write_stdin[1], passwd);
waitWithTimeOut(pid, 300, status);
close(write_stdin[1]);
close(read_stdout[0]);
};
}


int talkToPlink(struct pollfd *waitfordata ,int read_stdout,int write_stdin,const char *passwd, const char *outputFilename,const char *errFileName)
{
char buf[2048];
int pollRes=0;
unsigned long bread = 0;
while(1)
{
pollRes = poll(waitfordata,1,5*1000);
if(pollRes < 0)
{
printf("ReadWithTimeOut: Poll Error:%s",strerror(errno));
return -1; // pipe closed or other failure
}
memset(buf, 0, 2048);
bread = 0;
if(pollRes > 0)
if(waitfordata[0].revents > 0 )
if(waitfordata[0].revents != POLLIN)
break;
}
}

int waitWithTimeOut(pid_t pid, int timeout,int &status)
{
char filebuf[64];
snprintf(filebuf, 63, "/proc/%d/status", pid);
int timespent = 0;
int state=0;
while(timespent <= timeout){
FILE *fp = fopen(filebuf,"r");
if(!fp){
printf("no process\n\n");
return 0;
}
char buf[64];
while(!feof(fp)){
memset(buf, 0, 64);
fgets(buf, 63, fp);
if(!strstr(buf, "State"))
continue;
if(!strstr(buf, "zombie"))
break;
waitpid(pid, &state, WNOHANG);
if(WIFEXITED(state))
{
printf("WEXITSTATUSi1\n");
status=WEXITSTATUS(state);
kill(pid, SIGKILL);
waitpid(pid, 0, 0);
return 1;
}
sleep(1);
fclose(fp);
fp = NULL;
return 0;
} // end of while -- file reading..
fclose(fp);
fp = NULL;
timespent++;
sleep(1);
} // end of while -- time wait
kill(pid, SIGKILL);
waitpid(pid, 0, 0);
return 1;
}


Thanks,
Nagendra R