> /dev/null 2>&1

Seen this? You will ask either of the following question:

1) What is it?
2) I know it is input/output redirection but how is it working?

Now the answer for both of you.

In *nix world STDIN, STDOUT, STDERR are three common things that you must know.
Standard Input i.e. STDIN or 0 is something like keyboard.
Standard Output i.e. STDOUT or 1 is something like Monitor
Standard Error i.e. STDERR or 2 is something like ERROR

You can manipulate them. For eg,
Instead of typing from keyboard you can input from other medium using input redirection.
Like print < /file

Instead of displaying to monitor you can output to other medium using output redirection. Like echo something > /otherfile
You can use >> to append

Instead of displaying error to standard error you can use error redirection.
Like cat somefile 2> /dev/null
cat somefile 2> /somefile
Here /dev/null is something like dustbin. If you don't want your error to be seen then simply redirect it to the dustbin.

Now let me answer the second question

> /dev/null 2>&1 redirect both output and error to /dev/null
> /file 2>&1 redirect both output and error to /file

> redirects output to /dev/null
2>&1 redirect error to where > is redirected
So error also gets redirected to /dev/null


  1. Thankyou very very much. I always wondered what the *** was this all aobut. Thankyou again. Very nice.


Post a Comment

Comments are moderated. No spam please.

Popular posts from this blog

Perm Root HTC Desire Gingerbread 2.3.3

Increase Free Space On HTC Desire Android Phones

Lenovo Y510 surround sound in Ubuntu