Algorithm to read and write command line string - command-line

Question

I'm trying to write a program that can read a command string and validate it (get the name of the command and it's arguments), change those arguments and then rewrite the command string dynamically.
I'm looking for an Algorithm or regEx that can parse a command string. I'm familiar with DOS 6.2 and batch files but I know very little about Mac like terminal, unix, shell, etc which is what I'm using. I'm not sure if the arguments is a different syntax from one command to the next.
More info:
Things I have to do is validate that a command line is formatted correctly, for example, where paths to files have quotes around them or escape spaces if they are there. I would like it to be generic so that it can work with any command.
I'm using a Mac so I can test in Terminal.

Answer 1

#include<stdio.h>
main(int argc,char *argv[])
{
if(execlp(argv[1], argv[1], argv[2], "/usr/", (char *) 0)==-1)
printf("This is not valid command\n");
exit(0);
}
Run the program :
./a.out ls -lhrt
This program handled more than one options.
which directory you want change it instead of the "/usr" directory
You run the program dynamically and change the command and options .