In Linux, pipes connect the standard output of one command
to the standard input of another command.
Consider the ls command that was discussed
earlier. There are plenty of options available with
ls, but what if the contents of a directory
stream by too quickly for you to view them?
View the contents of the /etc directory.
How do you get a closer look at the output before it moves off the
screen?
One way is to pipe the output to a utility called
less. Known as a pager,
less allows you to view information one page (or
screen) at a time.
Use the vertical bar (|) to pipe the commands (as
shown in Figure 10-11).
Now we can view the contents one screen at a time. To move forward a
screen, press [Space]; to move back a screen, press
[b]; to quit, press [q].
 | How to Read Your Startup Messages |
|---|
| | To read startup messages more closely, at a shell prompt, type
dmesg | less. You'll be able to read the file
one screen at a time. To move forward, press the
[Spacebar]; to quit, press [Q].
|
Actually, pipes have already been introduced in this manual. In
previous references to man pages, you used the following command to
print them:
Here, the output of man ls is sent to a filter
called col with an option of
-b to help format the text for the printer. Then
that output is sent to the printer using the lpr
command.
For another example, type:
grep coffee sneakers.txt | lpr |
This will print every line in the sneakers.txt file that
mentions the word "coffee" (read more about
grep in the section called The grep Command).
The main difference between more and
less is that more
only lets you move forward through a file and
less lets you move backwards and forwards.
Let's take a look at the man page for more, but
this time, we'll open the page using more
— by piping man's output to
more.
