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I want to implement a linux shell interpreter which takes multiple piped commands such as "ls| grep c| sort | less" as input and gives the output on the command line as well as saves the output in a file in c, using pipes and tees only. I modified the code given in the answer in this link: Connecting n commands with pipes in a shell?

In my code, pipestr is the array of piped commands and parsed contains the space seperated arguments of a command i.e for the above example pipestr will have ["ls","grep c","sort","less"] and parsed for each of them would be : parsed[0]=["ls"], parsed[1]=["grep","c"] and so on.

I am getting the output on the command line, however nothing is being written to the file using the tee function? Kindly help.

int pipeex(int in,int out, char ** parsed)
    {
pid_t p;
p=fork();
if(p==0)
{
    if(in!=0)
    {
        dup2(in,0);
        close(in);
    }
    if(out!=1)
    {
        dup2(out,1);
        close(out);
    }
    if(execvp(parsed[0],parsed)<0)
    {
        printf("Command not executed\n");
        status=-1;
    }
}
else
{
    wait(NULL);
}
}

In the main function:

for(i=0;pipedstr[i]!=NULL;i++) 
{
     parseSpace(pipedstr[i],parsed);

        pid_t p;
        if(i!=noofpipe-1)
        {
            pipe(fd);
            pipeex(in,fd[1],parsed);
            close(fd[1]);
            in=fd[0];
        }
        else
        {
            pid_t p1;
            p1=fork();
            if(p1==0)
            {
                close(fd[1]);
                in=fd[0];
                if(in !=0)
                    dup2(in,0);
                fo = open("lf.txt", O_WRONLY | O_CREAT | O_TRUNC, S_IRWXU);
                statu = tee(STDOUT_FILENO,fo,INT_MAX, SPLICE_F_NONBLOCK); 
                close(fo);
                if(execvp(parsed[0],parsed)<0)
                {
                    printf("Command not executed\n");
                    status=-1;
                }
            }
            else
            {
                wait(NULL);
            }
        }
}
hidden_person
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  • I think you need to post more of your code as key elements are missing (e.g. the `tee` function). What you post should be downloadable as a single file, compile cleanly, and be runnable by a responder here. See: https://stackoverflow.com/help/mcve and https://stackoverflow.com/help/how-to-ask See my answers: https://stackoverflow.com/a/52825582/5382650 and https://stackoverflow.com/a/35570162/5382650 In the 2nd, see also: http://pastebin.com/Ny1w6pUh – Craig Estey Feb 17 '19 at 16:26
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    @CraigEstey tee(2) is a system call / wrapper in Linux. –  Feb 17 '19 at 16:54
  • @hidden_person post a mcve as required, but for one thing, notice that in the call to tee(2) after dup2(in, 0) you probably want to copy from stdin (0) not from STDOUT_FILENO (1). –  Feb 17 '19 at 16:59
  • @mosvy Well, bless me, it is. I hadn't heard of it, and I did a `man 3 tee` and got nothing, so I'll consider it for _my_ future use as well. – Craig Estey Feb 17 '19 at 16:59

0 Answers0