The commands that read their input from standard input could be used as receiver in a pipeline. For instance: `A | B` is a short form of `A > tmp.txt; B < tmp.t

The commands that read their input from standard input could be used as receiver in a pipeline. For instance: `A | B` is a short form of `A > tmp.txt; B < tmp.txt; rm tmp.txt` There are some commands that need literal arguments which is different than standard input. For instance the echo command. `echo < list.txt` will not work assuming you want to print the items inside the list. `echo itemA itemB itemC` will work. This is where xargs comes into play -- it converts the standard input stream to literal arguments among other things.