UNIX uses the concept of a pipe
to connect the standard output of
one program directly into the standard input of another program.
This is specified by separating the two commands with the pipe
operator, the vertical bar ( 
). The general format is:
command1 
command2 
...
For example, to
sort the output of the who command:
who 
sort
Of course, each command can have options and arguments.
The tee command can be used to send output to a file as well as to another command.
who 
tee whoout 
sort
This is the same as the previous example except that a file named whoout
is created containing the original who output. The sorted output
goes to standard output, the terminal screen. It is possible to set up multiple pipes. Commands that appear in pipe statements may include all the usual options and file designations.
ls -l | lp
This command pipes the output of the ls command to the printer via
the lp command.