Erle Robotics Unix Introduction Gitbook Free

Pipes

To see who is on the system with you, type

 who

One method to get a sorted list of names is to type,

 who > names.txt
 sort < names.txt

This is a bit slow and you have to remember to remove the temporary file called names when you have finished. What you really want to do is connect the output of the who command directly to the input of the sort command. This is exactly what pipes do. The symbol for a pipe is the vertical bar |

For example, typing

who | sort

will give the same result as above, but quicker and cleaner.

To find out how many users are logged on, type

 who | wc -l

As exercise using pipes, display all lines of list1 and list2 containing the letter 'p', and sort the result. (Remenber: grep command search for keyword-keyletter) Result: cat list1 list2 | grep p | sort

At this point you are ready to do something more practical with your erlerobot. In this tutorial explains how to blink a Led.It is a very good way of practicing some of the things you have learned till the moment.

working with erlerobot: