But cat can also perform a quick demonstration of two important
terms: standard input and standard output.
Standard input and standard output direct input and output (often referred
to as I/O) to the user. If a program reads from standard input,
it will, by default be reading from the keyboard. If a program writes to
standard output, by default it will be writing to the screen.
Let's start cat to see what this means. At the shell prompt, type:
cat
The cursor moves to a blank line. Now, in that blank line, let's type:
stop at sneaker store
and press the [Enter] key. Suddenly, your screen looks like:
[billy@localhost billy] cat
stop by sneaker store
stop by sneaker store
Figure 30: cat demonstrates standard input and standard
output
To quit cat now, just move the cursor to a blank line by pressing
[Enter] then press the [Ctrl] and [D] keys at the same time.
So it's not too exciting. But cat has just demonstrated the
definition of standard input and standard output. Your input was read from
the keyboard (standard input), and that input was then directed to your
terminal (standard output).
Summary: Standard input is often text which is entered from the
keyboard. Standard output is the place where information is sent, such as
your terminal (as shown in Figure 30).
Download
