Execvp not being executed n times in a loop - c

Question

Assume input is a pointer to array, which at each elements stores, "ls -l" at position 0, then cat helloworld.txt at position 1, and so forth, I wish to create the main parameter, which is ls, cat, pwd, and execute it. Essentially, what I am doing is I have a file with all those commands, I first store them in my input variable, which is declared as char *input[10]. Now I have what I need in that array, and I am able to extract the individual main commands, like ls, cat, and I wish to execute all of them.
For example,
if position 0 had ls -l, my first variable has ls and I wish to pass that to execvp and then position 1 might have cat sample.txt, now my variable first will be cat, and I pass that to execvp along with the entire cat sample.txt(which is input[i]), to execvp. For some strange reason, this is not working. How can I run all those commands in a loop in an execvp such that once it's done, all those commands have ran successfully. Here is my attempt, at the end of the first loop, I run an execvp, I expect that to finish, and then I extract further input, etc, etc.
Help me out.
for(i=0; i<lineCount; i++)
{
first = malloc(sizeof(char)*50);
for(j=0; j<strlen(input[i]); j++)
{
if(input[i][j]!=' ')
{
first[j]=input[i][j];
}
else
{
break;
}
}
execvp(first, input[i]);
}
I tried doing execp(first, input) but that didn't work either.

Answer 1

If you use execvp() once , the context of execution of the process that involved will be changed , except the pid of the process that called execvp , hence your loop won't work since once execvp() , there won't be any more iterations.
execvp() is mainly meant to be called by a child process , in your case for 'n' number of execvp() calls , there must have neen 'n' number of child processes forked,
Good Practices:
Using execl, execv, execle, execve, execlp, execvp , family of system calls , with child processes.
After the new process image is loaded to child , and after execution , collect the exit code of process launched , and perform any necessary error handling.
The child processes are now in a zombie state , the parent process must exexute wait()/waitpid() , and wait till all the child processes are terminated , and then exit.
-- Edit --
POC code for OP's reference
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
int main(void)
{
pid_t cpid;
int status = 0;
cpid = fork();
if (cpid == 0)
{
char *cmd[] = { "ls", "-l", (char *)0 };
int ret = execv ("/bin/ls", cmd);
}
wait(&status);
if(status < 0)
perror("Abnormal exit of program ls");
else
printf("Exit Status of ls is %d",status);
}

Answer 2

Here is what the opengroup exec manual says, in the first paragraph:
There shall be no return from a successful exec, because the calling
process image is overlaid by the new process image.
I suggest reading the opengroup fork manual, and using fork and exec in conjunction.

Answer 3

exec replaces the running process with the one you exec, and so it never returns on success because the process will be replaced.
If you want to run a bunch of processes, the simple way is to use a utility function like popen or system to run them. For complete control, use the usual UNIX fork/exec combo once for each command you want to run.