Multiple line output from execlp

Question

I am trying to return a multiple line output using execlp but am unsure of the exact method to do so. I have tried

#include <iostream>
#include <string>
#include <unistd.h>
using namespace std;

int main()
{
   string str = "echo ";
   str += "one \n";
   str += "two \n";
   str += "three \n";
   if(execl("/bin/sh","/bin/sh","-c",str.c_str(),(char*)NULL) == -1)
   {
      printf("Child Execution Failed\n");
      exit(1); 
   }                
   exit(0);
   return 0;
}

I basically want all of one , two and three to be printed in the shell. I get the following output though

one
/bin/sh: 2: two: not found
/bin/sh: 3: three: not found

Many thanks again!

Answer: Found a simple answer:

#include <iostream>
#include <string>
#include <unistd.h>
using namespace std;

int main()
{
   string str = "echo one\n";
   str += "echo two\n";
   str += "echo three\n";

   if(execl("/bin/sh","/bin/sh","-c",str.c_str(),(char*)NULL) == -1)
   {
      printf("Child Execution Failed\n");
      exit(1); 
   }                
   exit(0);
   return 0;
}

Answer 1

execlp replaces the current process that calls it with the program specified in execlp arguments. See the man page and note:

The exec() family of functions replaces the current process image with a new process image.

Having a loop trying to call execlp many times is pointless, as after the first call to execlp , your program is no longer executing. There are ways to use execlp in combination with fork or one of fork's variants) that can work, but there are easier options...

Instead, use popen to run a distinct child process and have a pipe to read its output from.