getenv, getenv_s

1) Searches for an environmental variable with name name

This function is not required to be thread-safe. Another call to getenv, as well as a call to the POSIX functions setenv(), unsetenv(), and putenv()

Modifying the string returned by getenv invokes undefined behavior.

2) Same as (1), except that the values of the environment variable is written to the user-provided buffer value (unless null) and the number of bytes written is stored in the user-provided location *len (unless null). If the environment variable is not set in the environment, zero is written to *len (unless null) and '\0' is written to value[0] (unless null). In addition, the following errors are detected at runtime and call the currently installed constraint handler function:

• name is a null pointer
• valuesz is greater than RSIZE_MAX
• value is a null pointer and valuesz is not zero

As with all bounds-checked functions, getenv_s is only guaranteed to be available if __STDC_LIB_EXT1__ is defined by the implementation and if the user defines __STDC_WANT_LIB_EXT1__ to the integer constant 1 before including <stdlib.h>

1) character string identifying the value of the environmental variable or null pointer if such variable is not found.

2) zero if the environment variable was found, non-zero if it was not found or if a runtime constraint violation occurred. On any error, writes zero to *len (unless len

#include <stdio.h>
#include <stdlib.h>
 
int main(void)
{
    const char *name = "PATH";
    const char *env_p = getenv(name);
    if (env_p)
        printf("Your %s is %s\n", name, env_p);
}

Your PATH is /home/gamer/.local/bin:/usr/local/bin:/usr/bin:/bin:/usr/share/games