Excel usage example in Linus operating system

Excel usage

#include <stdio.h>
#include <unistd.h>

int main() {
  pid_t ret;
  printf("welcome...pid=%d\n", getpid());
  ret = fork();
  if (ret < 0) {
    perror("fork");
    exit(1);
  }
  if (ret == 0) {
    printf("child--hello,pid=%d,ppid=%d\n", getpid(), getppid());
    int k;
    k = execl("/usr/bin/cal", "cal", "10", "2021", NULL);
    if (k < 0) {
      perror("execv");
      exit(1);
    }
    exit(0);
  } else // ret>0
  {
    printf("parent--hello,pid=%d,ppid=%d\n", getpid(), getppid());
    waitpid(-1, &status, NULL);
  }
  return 0;
}

 
Other Possible ways of using execl family of functions
execlp:-

execlp("cal", "cal", "10", "2018", NULL);

execv:-

char* argv[]={"cal","10","2018",NULL};
k=execv("/usr/bin/cal",argv);

execvp:-

char* argv[]={"cal","10","2018",NULL};
k=execvp("cal",argv);

Try this example:-

• Build and generate an executable from a C Program taking command line arguments
• Launch this executable using execl/execv.

 
Notes

• Overwrites child address space with resources of specified program
• Process remains same, but program/resources will change
• Any code after execl is redundant, if execl succeeds
• execl vs execlp
• Usage of execv, execvp, execvpe
• Usage of excecle

 
Observation & Understanding
 

• When do execl fails, what’ll happen in such case?
• What if, program launched by execl fails (failure/abnormal termination) – how to analyze?
• Matching of
  • execl 2nd param
  • argv[0] in launched program
  • cmd attribute in ps output