asked on

Redirecting stdin/stdout/stderr [Linux]

Hello,
i need to run a command-line program, read its stdout/stdin and write its stdin.
In few words i need to do what this python script does:

import popen2
r,w,e = popen2.popen3('mount -t reiserfs ./MyDisks/ecnrypteddisk ./mnt/mydisk -o loop,encryption=AES256,rw -p 0');
w.write('password');
w.close();
for line in e.readlines():
print 'E: ' + line
for line in r.readlines():
print 'R: ' + line

r.close();
e.close();

Thank you,
Luca

SOLUTION

stefan73

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stefan73

Ah, popen3 also dups stderr (fd=2). But then it gets messy for your program, as you need non-blocking I/O. You'd better just do a dup2 for stderr, also redirecting it to the stdout pipe.

lucat

ASKER

Hmmm why this doesn't work?
It segfault on me... even thought the "ls" command is correctly executed (i know it because if i write "kwrite" instead than "ls" kwrite shows up).
I believe i am doing something wrong with fscanf (if i comment it out it doesn't give any error).
Is it correct how i use dup2?

Thanx,
Luca

#include <stdio.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

int main()
{
      int fdin[2];
      int fdout[2];
      int fderr[2];
      pid_t pid;
      char s[256];

      pipe(fdin);
      pipe(fdout);
      pipe(fderr);

      pid = fork();
      if (pid == (pid_t) 0) {
            close(fdin[1]);
            close(fdout[1]);
            close(fderr[1]);
            dup2(fdin[0],STDIN_FILENO);
            dup2(fdout[0],STDOUT_FILENO);
            dup2(fderr[0],STDERR_FILENO);
            execlp("ls","ls",0);
      }
      else {
            close(fdin[0]);
            close(fdout[0]);
            close(fderr[0]);
            FILE* streamin;
            FILE* streamout;
            FILE* streamerr;
            streamin = fdopen(fdin[1],"w");
            streamout = fdopen(fdout[1],"r");
            streamerr = fdopen(fderr[1],"r");
            fscanf(streamout,"%[^]",s);
            printf("%s",s);
            close(fdin[1]);
            close(fdout[1]);
            close(fderr[1]);
            waitpid(pid, NULL, 0);
      }

      return 0;
}

ASKER CERTIFIED SOLUTION

ozo

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