Environment variables

Lesson

Each process has a list of NAME=value strings (the environment). char *getenv(const char *name) returns the value (or NULL). setenv / unsetenv mutate it; clearenv wipes it.

Children inherit a copy of the parent's environment. Useful for configuration that varies by deployment without changing code.

Code examples

const char *home = getenv("HOME");
if (home) printf("%s\n", home);

Common mistakes

• Treating environment values as trusted — they're user-controlled. Validate them.