Re: Procedure to uninstall nvidia drivers and restore nouveau

[PaulNM <debian@paulscrap.com>]

On 11/12/2013 02:56 AM, Alex Naysmith wrote:
> From the nvidia install procedure is the following command:
> 
> # aptitude -r install linux-headers-$(uname -r|sed 's,[^-]*-[^-]*-,,')
> nvidia-kernel-legacy-173xx-dkms
> 
> I can see the pipe | symbol and the regular expressions but I don't
> really understand what this command is doing.

It installs the linux headers related to the currently running kernel.
It takes the output of "uname -r" and pipes it to sed.  Sed is doing a
substitution, replacing the version numbers with nothing.

For example, on my lubuntu system:

paul@Serenity:~$ uname -r
3.11.0-13-generic
paul@Serenity:~$ uname -r | sed 's,[^-]*-[^-]*-,,'
generic
paul@Serenity:~$ echo linux-headers-$(uname -r|sed 's,[^-]*-[^-]*-,,')
linux-headers-generic

I used echo instead of aptitude, since I don't want to actually install
the package.

From:
http://www.gnu.org/software/sed/manual/html_node/The-_0022s_0022-Command.html

"The syntax of the s (as in substitute) command is
‘s/regexp/replacement/flags’."

From:
http://www.grymoire.com/Unix/Sed.html#uh-6

I believe [^-] in the regular expression means globally match anything
except a dash.  I'm a little weak on sed (and awk), so I might be a
little off on the specifics. I'm sure others will correct/elaborate for
me. :)

- PaulNM


> 
> 
> Alex