If you use just about any modern command line, you probably understand the idea of pipes. Pipes are the ability to connect the output from one program to the input of another. For example, you can more easily review contents of a large directory on a Linux machine by connecting two simple commands using a pipe:
ls | less
This command runs
ls and sends its output to the input of the
less program. In Linux, both commands run at once and output from ls immediately appears as the input of less. From the user’s point of view it’s a single operation. In contrast, under regular old MSDOS, two steps would be necessary to run these commands:
ls > SOME_TEMP_FILE less < SOME_TEMP_FILE
The big difference is that
ls will run to completion, saving its output a file. Then the
less command runs and reads the file. The result is the same, but the timing isn’t.
You may be wondering why I’m explaining such a simple concept. There’s another type of pipe that isn’t as often used: a named pipe. The normal pipes are attached to a pair of commands. However, a named pipe has a life of its own. Any number of processes can write to it and read from it. Learn the ways of named pipes will certainly up your Linux-Fu, so let’s jump in!