What does 2>/dev/null mean?

The > operator redirects the output usually to a file but it can be to a device. You can also use >> to append.

If you don't specify a number then the standard output stream is assumed, but you can also redirect errors:

> file redirects stdout to file
1> file redirects stdout to file

2> file redirects stderr to file

&> file redirects stdout and stderr to file
> file 2>&1 redirects stdout and stderr to file

/dev/null is the null device it takes any input you want and throws it away. It can be used to suppress any output.

Note that > file 2>&1 is an older syntax which still works, &> file is neater, but would not have worked on older systems.

In short, it redirects stderr (fd 2) to the black hole (discards the output of the command).

Some commonly used pattern for redirection:

command > /dev/null 2>&1 &

Run command in the background, discard stdout and stderr

command >> /path/to/log 2>&1 &

Run command, append stdout and stderr to a log file.

In Bash 4+, a shorter (but less readable) form is functional

command &>> /path/to/log

/dev/null is treated as black hole in Linux/Unix, so you can put anything into this but you will not be able to get it back from /dev/null.

Further, 2> means that you are redirecting (i.e. >) the stderr (i.e. 2) into the black hole (i.e. /dev/null)

Your command is:

grep -i 'abc' content 2>/dev/null 

Don't try to end with another forward slash like this - 2>/dev/null/ (it's not a directory).

grep -i 'abc' content will generate output which is displayed on your console, including any errors.

Specifying 2>/dev/null will filter out the errors so that they will not be output to your console.

In more detail: 2 represents the error descriptor, which is where errors are written to. By default they are printed out on the console.

\> redirects output to the specified place, in this case /dev/null

/dev/null is the standard Linux device where you send output that you want ignored.

First we need to talk about > operator. It redirect the output of left of symbol to right of symbol.

So it must thought as :

source_command > target_file

Other things that we must know

0 means stdin 
1 means stdout(useful output)
2 means stderr(error message output)

As default, it works as command 1 > target_file

As to /dev/null --> it is a special file that discards channel output redirect to it.

So in your question it means

Run the command and do not show me the error messages, discard them.