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Redirecting stdin/stdout/stderr [Linux]

lucat
lucat asked
on
Medium Priority
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Last Modified: 2008-02-01
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
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Top Expert 2004
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Top Expert 2004

Commented:
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.

Author

Commented:
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;
}
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