Hardware Reference
In-Depth Information
Standard Streams
Linux supports
standard streams,
a mechanism to allow the output of one program to be
fed into another one. This allows very powerful combinations of programs to be connected
together on the command line to process data. There are three standard streams:
❍
Standard in (
stdin
) - Used for input.
❍
Standard out (
stdout
) - Used for output.
❍
Standard error (
stderr
) - Another sort of output, reserved for reporting error
messages.
Essentially standard streams can be thought of as special iles. One program will write to its
stdout
stream, which can be
piped
(think of the commands as stages in a pipeline) to the
stdin
stream of another. This program reads from its
stdin
to receive the data. If no
other program is speciied, by default
stdin
will be taken from the keyboard, and
stdout
will be displayed on the screen in the terminal.
The
|
character is used to indicate that the output of one program should be piped into
another. For an example of how pipes work, imagine that you want to sort the list of the
iles in your home directory in reverse order. The command
ls
lists the contents of a direc-
tory to
stdout
. The
sort
command takes input from
stdin
, orders it and sends it to
stdout
. The
-r
argument tells
sort
to reverse the ordering. So, to reverse sort a list of
contents of a directory, in a terminal type
ls | sort -r
****sort uniq wget cat grep >
To test the analysis program, use the
cat
program to pipe the contents of your
birddata.
txt
ile into your Python program by typing the following in a terminal:
cat birddata.txt | python analyseBirdDataBasic.py
With
DEBUG=1
set, the program will go through the state machine, process the sensor log
entries and print a description of what it thinks the bird is doing.
Dealing with Sensor Noise
In everyday life, someone may say that an environment is too noisy for him or her to hear
properly.
Noise
is the sound that is unwanted and getting in the way of what the listener
