Why does ls give different output when piped

Question

Printing to terminal directly:

$ ls
a.out  avg.c  avg.h

Piping to cat

$ ls | cat
a.out
avg.c
avg.h
         


        

Answer 1

ls can actually determine if it's outputting to a terminal or a file (with the isatty library call). If it detects a console, it will try to make it more compact for easier viewing.