Mar 21, 2015 01:05 AM
(This post was last modified: Mar 21, 2015 09:22 AM by mr.cracker.)
I was trying to redirect childs STDIN and STDOUT to pipes using dup2().
child has : execl("/bin/sh")
I want to give commands from Parent.
Child executes it. Write o/p to stdout, which is redirected to pipe.
Then parent read from pipe, o/p to stdout of parent.
my code is,
it got stuck on here,
I dont get any output.
Why child does not write into pipe2[1] ?
I think thats why system waits for some data in read() function.
Where i got mistake?
How can i make it work?
child has : execl("/bin/sh")
I want to give commands from Parent.
Child executes it. Write o/p to stdout, which is redirected to pipe.
Then parent read from pipe, o/p to stdout of parent.
my code is,
Code
#include<stdio.h>
#include<wait.h>
#include<unistd.h>
#include<stdlib.h>
#include<string.h>
int main(){
pid_t pid;
int n, len;
int pipe1[2], pipe2[2];
char buff[1024], data[4096];
pipe(pipe1);
pipe(pipe2);
if( (pid = fork()) < 0){
return 1;
}else if(pid == 0){ //child
close(pipe1[1]); //child closes write end of pipe 1 ( fd1[1]), and
close(pipe2[0]); //child closes read end of pipe 2 (fd2[0]).
dup2(pipe1[0], STDIN_FILENO); // pipe1[0] read pipe, which is opened in child. And it's companion
// pipe1[1] write pipe is opened in parent.
// whatever write into pipe1[1] will be recived by stdin of child.
dup2(pipe2[1], STDOUT_FILENO);
execl("/bin/sh", "/bin/sh", (char *)0);
exit(0);
}
//parent
printf("parent pid: %d\n", (int)getpid());
close(pipe1[0]); //parent closes read end of pipe 1 ( fd1[0])
close(pipe2[1]); //parent closes write end of pipe 2 (fd2[1])
while(1){
printf("\nenter command: ");
//read pathname
if(fgets(buff, 1024, stdin) == NULL){
printf("error in fgets");
exit(1);
}
len = strlen(buff); // fgets() guarantees null byte at end
//if(buff[len - 1] == '\n')
// len--; //delete newline from fgets
//write pathname to ipc channel
if(write(pipe1[1], buff, len) != len){
printf("write error in client\n");
}
printf("command written to child: %s\n", buff);
/* read from IPC, write to standard output */
n = read(pipe2[0], buff, 4096);
printf("am reading\n");
if(write(STDOUT_FILENO, buff, n) != n ){
printf("write error inside while in client\n");
}
}
}it got stuck on here,
Code
while((n = read(pipe2[0], buff, 4096)) > 0){Why child does not write into pipe2[1] ?
I think thats why system waits for some data in read() function.
Where i got mistake?
How can i make it work?