Minor Command Question

[MadDawg010]

Can anyone explain exactly what the command below does?

sudo aptitude purge `dpkg -l | grep "^rc" | tr -s ' ' | cut -d ' ' -f 2`

I found this "super clean" command while looking up the difference between clean and autoclean. I used this to reclaim some space, and it did so quite well. I want to recommend this to users, but I need to be able to fully explain what this does; I don't want to just tell a user to throw this into their terminal prompt without letting them know exactly what happens.

[warfacegod]

If you don't want to recommend it with out understanding it entirely then why would you use it on your own system?

[MadDawg010]

I have a virtual machine I can test unusual commands on, so if I nuke the VM, nothing is lost.

[warfacegod]

I would opena Terminal Type "man" bfore each part of the code, Example:

man grep

Enter. man is short for manual and will give a description of each command.

[sisco311]

sudo = run the command as root
aptitude = package manager
purge = purge package
`command` or $(command) = replace command name with the output of the command

man bash | less +/"Command Substitution"

dpkg -l = list packages
dpkg -l | grep "^rc" = list only the lines which begin with rc
dpkg -l | grep "^rc" | tr -s ' ' | cut -d ' ' -f 2 = list only the second column (package name) of the lines

[gnack]

Another version:

sudo aptitude purge `dpkg -l | grep '^rc' | awk '{print $2}'`

dpkg -l lists all packages installed or otherwise; the first two columns of each line indicate that packages state:

Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Cfg-files/Unpacked/Failed-cfg/Half-inst/trig-aWait/Trig-pend
|/

So, grep '^rc' says find the lines with "rc" at the beginning - the desired action is "Remove" and the status is "Cfg-files" (only config files exist on the system). For example:

rc nvidia-glx-180 180.44-0ubuntu1 NVIDIA binary Xorg driver
rc nvidia-settings 180.25-0ubuntu1 Tool of configuring the NVIDIA...

The tr/cut or awk command just grabs the package name (nvidia-settings)

aptitude purge removes the package/config from the system

[audiomick]

I would have suggested the same as warfacegod.

[MadDawg010]

Awesome, thanks sisco311. I was a little confused after reading all the manual entries for the separate commands.

Thanks for your input as well, warfacegod. I had somehow managed to completely forget about the man command. I guess this is what school does to me.

This thread is solved.

[gnack]

And adding an -s to the aptitude command will simulate the purge just in case you're unsure:

sudo aptitude -s purge ...

[MadDawg010]

Ah, thanks for the additional input, gnack.