Are environment variables replaced, copied or shared when calling exec family? - c

Question

I am trying some exec family functions in C and I have few questions concerning environment variables, here's my code:
find.c
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main(int argc, char *argv){
char *line = getenv("LINE");
char *target = getenv("TARGET");
if(!line || !target){
printf("LINE or/and TARGET not found\n");
return 1;
}
if(strstr(line,target))
puts(line);
return 0;
}
process.c
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int main(){
putenv("LINE=Hello world");
putenv("TARGET=Hello");
execl("./find","./find",NULL);
return 0;
}
output on "gcc process.c -o process && ./process"
Hello world
Quick explanation of the code.
find.c needs to read two environment variables and check if the TARGET variable value is a substring of the LINE variable value. If so, then print the LINE variable value.
process.c replace itself by executing find.c.
Questions
Knowing that the correct way of doing this is using execle, why did the program process.c work using execl and putenv ? In other words, creating environment variable in a process that get replaced doesn't replace the environment variable as well if not passed via execle ?
Does forking a process has the same answer to the above question ? So forking a process copies, replace or share the environment variables ?
Thank you

Answer 1

Knowing that the correct way of doing this is using execle, why did the program process.c work using execl and putenv?
This is explained in the man page:
The execle() and execvpe() functions allow the caller to specify the environment of the executed program via the argument envp. [...] The other functions take the environment for the new process image from the external variable environ in the calling process.
Note that environ is what's modified by putenv.
Does forking a process has the same answer to the above question ?
Forking duplicates the environment variables. From the man page:
The new process, referred to as the child, is an exact duplicate of the calling process, referred to as the parent, except for the following points:
[... list of points, none of which refer to environment variables ...]