7.1 Advanced Directory and File Management Using the Command Line
7.1.6 Command piping
One of the most powerful metacharacters is the pipe (|). The pipe takes the standard output of one command and passes it as standard input into a following command. In effect, pipes enable you to build a miniature program. The pipe symbol is sometimes referred to as a double vertical bar and is found below the backspace key. You must always have a command on each side of a pipe. Spaces between the commands and the pipe are optional.
Command Format:
command | command

Displaying Command Output One Screen at a Time
One of the most common uses of the pipe metacharacter is to send the output of a
ls command to the more command to enable you to see a long directory listing one screen at a time. The first example in Figure shows this basic use of the pipe. The standard output from the command to the left of the pipe becomes the standard input for the command on the right side of the pipe.

By rolling your mouse over Figure , you can view explanations for the multiple commands interconnected by multiple pipes. Several commands are introduced here that you will work with later in the course.

The second example in Figure uses the ps -ef command to display a detailed list of all processes running on the system, and that output is passed as input to the grep command, which searches for the string "brad" in all processes. The resulting output of the grep command is passed as input to the sort command, which sorts the output using the Process ID (PID). The sorted output then becomes input to the tail command, which selects only the last 10 lines of output. That output is then sent to the default line printer lp.

Interactive Media Activity (Flash, 95 kB)
  Command Piping

In this media activity, you are logged in as user2 and your current working directory is: /home/user2/dir2. Refer to the Class File Tree Structure by clicking the 'tree' button located on the Menu Bar and type the commands that would accomplish the requested objectives. 
Note: Be sure to press enter after each one. Click on step 1 to begin.

Lab Activity (Adobe Acrobat Reader, 45 kB)
  Redirection and Piping

In this lab, you will use advanced UNIX commands to accomplish redirection and piping.