Ubuntu: Up and Running

Using Pipes

A little earlier we looked at alternative ways of using the more and grep commands by piping output through them using the | operator. Pipes are such a useful device that you will see them used in a variety of ways, often with multiple commands piped together to produce a final output. For example, take a look at the following composite command:

ps -ax | sort -k5 | less

The ps program, in conjunction with the argument -ax, displays all the background processes running on your computer, and is covered in more detail in the section System Processes. On its own, ps -ax will display many screens full of information; and the last few lines will look like Figure 7-12.

The processes are listed in order of when they were started (as indicated by the numbers in the first column). So, to quickly search through the list and find processes you may be interested in, you can use the sort command with the -k5 option. This causes a sort to occur on the fifth column (as defined by the end of a section of whitespace), which is the one containing the process path and filenames. This results in the screen grab shown in Figure 7-13.

This is an improvement, but we can do even better by also adding the less command, which is an enhanced version of more. The less command makes it easier to move back and forth in the output because it supports the cursor keys as well as Enter and the space bar.

So, the combined result is to list all the current processes alphabetically, displayed in a manner that ...