We use the < symbol to redirect the input of a command.
The command sort alphabetically or numerically sorts a list. Type
sort
Then type in the names of some animals. Press [Return] after each one.
dog
cat
bird
ape
^D (control d to stop)
The output will be
ape
bird
cat
dog
`
Using < you can redirect the input to come from a file rather than the keyboard. For example, to sort the list of fruit, type
sort < biglist
and the sorted list will be output to the screen.
To output the sorted list to a file, type,
sort < biglist > slist
Use cat to read the contents of the file slist.