sudo issue during echo something to a root file

Question

I have a problem, during write something into a root file:

$ ll /sys/bus/usb/devices/3-2/power/wakeup
-rw-r--r-- 1 root root 4096 Feb 16 17:28 /sys/bus/usb/devices/3-2/power/wakeup
$ sudo echo disabled > /sys/bus/usb/devices/3-2/power/wakeup
bash: /sys/bus/usb/devices/3-2/power/wakeup: Permission denied

even it did not ask me for password.

How can I solve this?
Why I can't use sudo directly?

`echo disabled | sudo tee /sys/bus/usb/devices/3-2/power/wakeup > /dev/null` — Costas, Feb 16 '15 at 09:32
@Costas, thanks, and can you tell me why I can't directly use `sudo`? — How Chen, Feb 16 '15 at 09:34
In your line at fact there are two commands: `echo` and `>` (redirection). First is sudoed, but the second didn't. — Costas, Feb 16 '15 at 09:36

score 1 · Accepted Answer · answered Feb 16 '15 at 09:35

You cannot use sudo with redirection, because the redirection is done by your original shell which runs as your own user code. It tries to set up a file descriptor for the file mentioned after the >, which fails as your user is not able to write to it.

Costas's method works, as does spawning a subshell:

sudo sh -c "echo disabled > /sys/bus/usb/device/3-2/power/wakeup"

sudo issue during echo something to a root file

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