Take the 2-minute tour ×
Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

I understand that the standard to redirect to is /dev/null, but why not use /dev/zero? Does it not have the same effect?

Another question, what do all the 1>> 2>> &>> >>& and whatnot mean for redirection

share|improve this question

1 Answer 1

Using /dev/zero has the same effect as /dev/null when redirecting output to it. There is no reason not to use it. The latter is just more commonly found in examples and thus has become more popular.

As for redirection, you should check your shell's manual. The Bash Hackers wiki has a tutorial on redirection and another reference page.

Basically,

  • > redirects output to a file

  • >> when redirecting appends to a file (or creates it when it doesn't exist), whereas > truncates and therefore deletes file contents

  • n>, where n is the number of the file descriptor, redirects output of that descriptor to a file. Typically 1 and 2 are used, being stdout and stderr, respectively.

  • m>&n redirects file descriptor m's output to n, so you could combine, for example, stdout and stderr: > /dev/null 2>&1

  • &> also combines stdout and stderr

share|improve this answer
    
Well, there is a difference. If you are redirecting the input, /dev/null gives nothing, whereas /dev/zero gives zeros. –  YtvwlD Jun 16 at 9:59
1  
@YtvwlD That's why I said, "when redirecting output to it". Of course they have different uses for input. –  slhck Jun 16 at 10:47
    
Does >&- /really/ have the same effect as > /dev/null? Perhaps I'm being too pedantic here, but from where I'm sitting they look quite different. –  Robbie Mckennie Jun 17 at 8:22
    
@RobbieMckennie You're right, it doesn't work apparently. I took that info from the Wiki but didn't check at the time. –  slhck Jun 17 at 8:33
    
fyi: en.wikipedia.org/?title=/dev/zero "All write operations to /dev/zero succeed with no other effects" –  akira Jun 18 at 9:38

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.