exec error handling

If errors occur while executing exec*(), it will return to the program and continue execution. The return value is -1, and errno is set to indicate the error.

/* Exec/exec_error.c */
#include <stdio.h>
#include <unistd.h>
#include <errno.h>
int main(int argc,char *argv[])
{
    printf("Try to execute lss\n");
    execl("/bin/lls","lls",NULL);
    printf("execl returned! errno is [%d]\n",errno);
    perror("The error message is :");
    return 0;
}

In this program, you can see the line execl returned!... is printed, indicating that execl() returns to the main function and the execution continues. errno is a global variable that stores the error number. You can check the manual for the error reason, however, you can print in a human-friendly way by using perror().