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

So that each line is one entry only, allowing the command the output is piped to to work as would likely be expected. For example (given your ls output), the following would probably not be what you want:

$ ls | sort -r
a.out  avg.c  avg.h

But because sort didn't know there was more than one item per line, it couldn't do anything. Compare this to what actually occurs:

$ ls | sort -r
avg.h
avg.c
a.out

You can achieve the (unexpected) first behavior by passing -C to ls.