simply appends the output of the ls command to an already existing le
named filelist.txt. If the le does not exist, it is created.
2 Redirections also works the other way round. Instead of using the standard
input from the keyboard for a command, you can use a le as input:
sort < filelist.txt
This will force the sort command to get its input from the contents of filelist
.txt. The result is shown on the screen. Of course, you can also write the result
into another le, using a combination of redirections:
sort < filelist.txt > sorted_filelist.txt
3
If a command generates a lengthy output, like ls -l may do, it may be useful
to pipe the output to a viewer like less to be able to scroll through the pages.
To do so, enter
ls -l | less
The list of contents of the current directory is shown in less.
The pipe is also often used in combination with the grep command in order
to search for a certain string in the output of another command. For example,
if you want to view a list of les in a directory which are owned by the user
tux, enter
ls -l | grep tux
7.11 Starting Programs and Handling Processes
As you have seen in Section 7.7, “Editing Texts” (page 100), programs can be started
from the shell. Applications with a graphical user interface need the X Window System
and can only be started from a terminal window within a graphical user interface.
For example, if you want to open a le named vacation.pdf in your home directory
from a terminal window in KDE or GNOME, simply run okular ~/vacation.pdf (or
evince ~/vacation.pdf) to start a PDF viewer displaying your le.
When looking at the terminal window again you will realize that the command line
is blocked as long as the PDF viewer is open, meaning that your prompt is not
available. To change this, press [Ctrl] + [Z] to suspend the process and enter bg to
send the process to the background. Now you can still have a look at vacation.pdf
while your prompt is available for further commands. An easier way to achieve this
is by sending a process to the background directly when starting it. To do so, add
an ampersand at the end of the command:
okular ~/vacation.pdf &
104 Start-Up
