[CentOS] backups and md5 all in one while splitting

Ross S. W. Walker rwalker at medallion.com
Mon Nov 12 23:05:52 UTC 2007

Well in bash/sh the () means execute in a sub-shell. If you redirect or pipe output from one process to a command in a sub-shell it will be redirected or piped (whatever the original was) to the command being executed in the sub-shell.

You can also use $(command) as a command-line variable that will substitute the output of the command during evaluation.

# mkinitrd /boot/initrd-$(uname -r).img $(uname -r)


-----Original Message-----
From: centos-bounces at centos.org <centos-bounces at centos.org>
To: CentOS mailing list <centos at centos.org>
Sent: Mon Nov 12 17:57:11 2007
Subject: Re: [CentOS] backups and md5 all in one while splitting

Ross S. W. Walker wrote:
> 'tee' splits the stdin into multiple output streams.
> The first instance of tee you listed gave it a file name and a pipe to 
> output the stdout to.
> The second instance did a redirection to a sub-shell which then passed 
> it to 'split' and it also had a pipe.
> -Ross

How does this sub-shell redirection work?  Can someone explain the 
syntax to me or shoot me a link to a doc somewhere? 


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