My system is macOS I try to run the count_occurrences script directly from the current directory count_occurrences Alice_in_Wonderland.txt, but the shell (zsh in my case) can't find it, it hints zsh: command not found: count_occurrences, only if i can run with ./count_occurrences Alice_in_Wonderland.txt

but in the lectures, i noticed that lecturer run with count_occurrences Alice_in_Wonderland.txt