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Implementation of ls | wc command
  • Difficulty Level : Expert
  • Last Updated : 30 Apr, 2018

ls | wc command : Using ls|wc, we can count new lines, words and letters of all files of current directory. We can see from the following after execution of the code we get same results.

Prerequisites :ls command | wc command | piping in linux

Approach : First, we have to use pipe for inter process communication over an array where a[0] is used for reading and a[1] is used for writing. We can replicate the process using fork. In the parent process, standard output is closed so that output of ls command will go to a[0] and similarly standard input is closed in children process. Now, if we run the program output will be as same as command of linux ls|wc.

Below is the implementation of above approach :




// C code to implement ls | wc command
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include<errno.h>
#include<sys/wait.h>
#include <unistd.h>
int main(){
  
    // array of 2 size a[0] is for
    // reading and a[1] is for
    // writing over a pipe    
    int a[2];
  
    // using pipe for inter
    // process communication
    pipe(a);
  
    if(!fork())
    {
        // closing normal stdout
        close(1);
          
        // making stdout same as a[1]
        dup(a[1]);
          
        // closing reading part of pipe
        // we don't need of it at this time
        close(a[0]);
          
        // executing ls 
        execlp("ls","ls",NULL);
    }
    else
    {
        // closing normal stdin
        close(0);
          
        // making stdin same as a[0]
        dup(a[0]);
          
        // closing writing part in parent,
        // we don't need of it at this time
        close(a[1]);
          
        // executing wc
        execlp("wc","wc",NULL);
    }
}





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