[ale] Redirection using sudo...?

[Michael B. Trausch]

On Tue, June 13 2006 15:15, Geoffrey wrote:
> Michael B. Trausch wrote:
> > Okay, so I know that the shell itself implements redirection.  This is
> > not a problem for me, as I use various forms of redirection and piping
> > and such all the time.  However, I have wondered if there is a way to
> > change how that works.
> >
> > Sometimes, I want to change something in /proc or /sys.  Doing
> > something like:
> >
> >  $ sudo echo "newvalue" > /sys/something
>
> Have you tried quoting the command?
>
> sudo 'echo "newvalue" > /sys/something'
> 

That doesn't quite work because it doesn't start a subshell.  I was looking 
at the problem from the wrong angle, due to an errant assumption on my 
part.  'sudo' handles the execution of the program itself, instead of using 
a subshell to do it in.  Thus:

fd0man at fd0man-laptop:~$ sudo 'echo fi > /fi'
sudo: echo fi > /fi: command not found
fd0man at fd0man-laptop:~$

... does not work because it then interprets the entire string as a command 
that it has to execute.  You *could* have a file named that on the 
filesystem and execute it, but it would terribly bad form.

Likewise, 'sudo -i' doesn't work in this way, either:

fd0man at fd0man-laptop:~$ sudo -i 'echo fi > /fi'
-bash: echo fi > /fi: No such file or directory
fd0man at fd0man-laptop:~$

However, the one way that does work is:

fd0man at fd0man-laptop:~$ sudo sh -c 'echo fi > /fi'
fd0man at fd0man-laptop:~$ cat /fi
fi

... because you are then passing the string to bash to interpret as a 
command.  Makes perfect sense now that I have seen somebody else do it -- 
it made me hit myself on the head.  :)

	- Mike
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