The tools, that all perform only a single operation can be combined to perfom complex operations on the data. This feature is realized with the operating systems pipe mechanism. In general, two programs, that are connected through a pipe, communicate over standard in and the standard output. The first porgrams output us taken as the second programs input. Mostly the pipe command is used when the output of a program shell be formatted or a special information should be extracted from any program output
ls -al | more
Often the contents of the directory is too long to fit a single screen. As a result, the first lines of the directory would vanish at the top of the screen. By using the more command, the output is stopped, whenever the sceen is full.
ps -al | grep jens
When checking the running processes of a system one is often interested in processes that belong to a certain person or those of a special program. The data of all other processes can be surpressed by the grep option. Only the line which contains the given word will be printed out.