2. Redirecting standard input
A command that makes use of standard input is cat (which is a
shortening for concatenate). It usually takes one or more files as
arguments and outputs their contents to the screen, joined together.
cat ls-output.txt ls-error.txt
However if no files are given as arguments it just reads lines from the standard input (keyboard by default) and writes them to the standard output (screen by default). Let's try it:
cat
Type a couple of lines and thes press "Ctrl-d" to tell cat that it
has reached the end of file (EOF) on standard input.
If we redirect the standard output to a file, then it can be used to create short files. For example try these:
cat > lazy_dog.txt
The quick brown fox jumped over the lazy dog.
Press "Ctrl-d" at the end.
cat lazy_dog.txt
To redirect the standard input (stdin) we can use the
redirection operator "<", like this:
cat < lazy_dog.txt
We have changed the source of standard input from the keyboard to the
file lazy_dog.txt.