cc shadow_cracker.c -lcrypt -o bruteforce -Wall -std=c11 -pedantic

bruteforce <dictionary file> OR bruteforce <path/to/etc/shadow> <dictionary file>

This will take a long time especially if you use a large dictionary file.

Wikipedia page on /etc/passwd and /etc/shadow

man page for crypt

cracker.py <path/to/dictionary/file>

Because Python's spwd module isn't as robust as <spwd.h> in C.