Redirecting outputs, Forking/Piping

Posted on 2003-11-21
Last Modified: 2010-04-15
First time playing around with forks and pipes.  Basically say if i have someone input a command "command1 P command2 | command3".   In this case, the key value P will direct the standard error of command1 to standard in of command2 and standard output of command1 directed to the pipe '|' after command2.  I know i will need to create a new pipe, fork it and get the input from parent thru fd 2 somehow.  Thanks.
Question by:aomega
LVL 84

Accepted Solution

ozo earned 100 total points
ID: 9801638
#include <stdio.h>
#include <unistd.h>
char *cmd0[]={"date","-u",0};
char *cmd1[]={"tr"," ","\n",0};
char *cmd2[]={"cat","-ve",0};
char *cmd3[]={"tr","$","_",0};
char **cmd[]={
  (char **)&cmd0,
  (char **)&cmd1,
  (char **)&cmd2,
  (char **)&cmd3,

#define N (sizeof(cmd)/sizeof(*cmd))
    double s0,s1;
    int pid[N];
    int fildes[N-1][2];
    int i;
    for( i=0; i<N; i+=1 ){
        if( i < N-1 ){ pipe(fildes[i]); }
        if( (pid[i]=fork())>0 ){
            if( i > 0 ){
        }else if( pid[i]<0 ){
            perror("fork"); exit(1);
            if( i>0 ){
            if( i<N-1 ){
            perror(cmd[i][0]); exit(1);
    for( i=0; i<N; i+=1 ){
        int s;

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