Redirection in Linux/Unix

Input/output Redirection in Linux

• The standard input (stdin) device is the keyboard.

• The standard output (stdout) device is the screen.

Linux, is a very flexible system and we can change the standard input / output devices. Let's learn how this re-direction works

Output Redirection

The '>' symbol is used for output (STDOUT) redirection.

Example:

ls -al > listings

Here the output of command ls -al is re-directed to file "listings" instead of our screen.

Note: Use the correct file name while redirecting command output to a file. If there is an existing file with the same name, the redirected command will delete the contents of that file and then it may be overwritten."

If we do not want a file to be overwritten but want to add more content to an existing file, then we should use '>>' operator.

We can re-direct standard output, to not just files, but also devices!

$ cat music.mp3 > /dev/audio

The cat command reads the file music.mp3 and sends the output to /dev/audio which is the audio device. If the sound configurations in our PC are correct, this command will play the file music.mp3.

Input redirection

The '<' symbol is used for input(STDIN) redirection

Example: The mail program in Linux can help us to send e-mails from the Terminal.

we can type the contents of the email using the standard device keyboard. But if we want to attach a File to email we can use the input re-direction operator in following format -

Mail -s "Subject" to-address < Filename