CODEWITHSUNDEEP
linuxbashshellio-redirection
xsimplex
xsimplex

Reputation: 87

What does the expression "< /dev/null some_command" do?

I am somewhat familiar with redirecting and know that /dev/null can be used for hiding output, for example with

some_command > /dev/null

but I encountered the usage

< /dev/null some_command

in this ArchWiki article and would like to understand what it does.

My first guess is that it is equivalent to

some_command < /dev/null

but if this guess is correct, what is the benefit of redirecting /dev/null to a command?

Upvotes: 2

Views: 143

Answers (1)

Barmar
Barmar

Reputation: 781068

Yes, they're equivalent. I/O redirection can be put anywhere on the command line.

When reading, /dev/null returns EOF immediately. Redirecting input from /dev/null is useful if you want to prevent the application from trying to read from whatever its initial standard input is, e.g. the terminal.

A common use of this is when running a program in the background via SSH and you want the SSH connection to close immediately. The connection won't close until all the file descriptors referring to it are closed, so you redirect all the standard descriptors:

ssh servername 'somecommand </dev/null >/dev/null 2>&1 &'

Upvotes: 5

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