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I want one or two line description about the following command line:

grep -i 'abc' content 2>/dev/null 
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3 Answers 3

up vote 25 down vote accepted

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

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

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

Some more common use case

command > /dev/null 2>&1 &

run command in background, discard stdout and stderr

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

run command and redirect stdout and stderr to log file

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This grep command has a wrong syntax, It should be something like

grep -ri content /support/security/bulletins/ 2> /dev/null

and the 2> /dev/null means to redirect all errors produced by this command to /dev/null, that is discard them, and don't display them to the screen (or where the standard error file descriptor is currently pointing). /dev/null is a file that when you write data to it they go nowhere.

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There is absolutely nothing wrong if you use 2>/dev/null. These 2 are equivalents: > file and >file. And why grep -ri? –  Radu Rădeanu Sep 26 '13 at 9:02
By the way, he could also be looking for the string /support/security/bulletins/ in the file called content =). –  Alaa Ali Sep 26 '13 at 9:06
@RaduRădeanu the wrong syntax is not on 2> but he has probably reversed the grep arguments, since otherwise grep is unlikely to produce lots of errors, except not being able to open a file named "content". –  sivann Sep 27 '13 at 12:24
@sivann That's a bad assumption. So, where is the wrong syntax? The OP doesn't said nothing about this... He just wanted to know what it means 2>/dev/null –  Radu Rădeanu Sep 27 '13 at 15:02

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