Linux : Use of Pipes in commands

A pipe ( | ) is used to send output of one command to some other command. Many a time, use of pipe simplifies our task to a great extent. I'll discuss a few examples

Count number of files in a directory

ls | wc -l

List all users on a system who are running some processes (process owners)

ps -ef | cut -d " " -f1 | sort | uniq

List all process-listings that contain the word "mozilla"

ps -ef | grep mozilla

Find the word "services" in all .htm files

find . -name "*.htm" | xargs grep "services"

Sort lines in a file and print on the console

cat filename | sort

Killing mozilla

ps -ef | grep "mozilla" | cut -f1 | xargs kill

Print last 10 lines of a file

tail filename | lpr

Here's a good page on Linux Tips.

This wikipedia page has more information on unix pipes.