The commands normally take their input from the standard input device keyboard. Using Input redirection concept, we can have their input redirected from a file. To redirect standard input from a file instead of the keyboard, the '<' character is used.
$ cat file1 monday tuesday wednsday thursday friday saturday sunday
The above is the content of file1
$ sort < file1 friday monday saturday sunday thursday tuesday wednsday
here insted of taking input from keyboard, we redirected it from the file1 and sort it in ascending order.