[SOLVED] a (potentially useful) command pipe

bluethundr · 05-07-2010, 10:42 AM

I'm trying to get a little better at piping together unix commands.

Here's one that I thought might be useful if I could actually get it working!

Code:

dpkg -l | grep cups |  awk '{print $2}' > foo | aptitude purge < foo

any thoughts?

pljvaldez · 05-07-2010, 10:54 AM

You might try using the back quote instead (on the ~ key). This will execute cat foo, which should be whatever text is in the file foo.

Code:

dpkg -l | grep cups |  awk '{print $2}' > foo | aptitude purge `cat foo`

bluethundr · 05-07-2010, 11:33 AM

hmmm.. I grok... but the above seems to cause an infinite loop! So I suppose I would have to write a small script that would feed apt-get the correct number of 'yeses' to get the job done...

pljvaldez · 05-07-2010, 11:49 AM

I think there's a -y switch in aptitude that will assume yes. Can you post your file "foo" just so I can see what's in it (I'm assuming it's a bunch of package names, but I'm not in front of my Lenny box to test it).

grail · 05-07-2010, 12:19 PM

Am I understanding that is just to see how to play with pipes and redirection?
As obviously this could have all been much shorter.

ntubski · 05-07-2010, 12:53 PM

You can't write to and read from a file in a single pipeline: all the programs run in parallel so the contents of the file will not be deterministic.

bluethundr · 05-07-2010, 12:53 PM

Quote:

Originally Posted by bluethundr

hmmm.. I grok... but the above seems to cause an infinite loop! So I suppose I would have to write a small script that would feed apt-get the correct number of 'yeses' to get the job done...

yes, reminding me of the use of back ticks and clueing me on the use of the -y switch was the magic answer!

Code:

dpkg -l | grep cups | awk '{print $2}' > foo | aptitude purge -y `cat foo`

And to answer your question.. yes 'foo' was just a list of package names..

thanks for playing!

lugoteehalt · 05-07-2010, 02:05 PM

Here's my favorite:

In a terminal, say inside X, do:

Code:

$ cat > pipe0
load of
bollocks<return>

Now, *in another terminal*, say outside X, do:

Code:

$ cat < pipe0

Neat eh?

And it allows you to paste between X and the black screen.

Close the thing in the first terminal with ctrl+d, end of file. Sorry should have said pipe0 is a 'named pipe'; use mkfifo pipe0 to make it??

cantab · 05-07-2010, 04:14 PM

Can't you just do

Code:

dpkg -l | grep cups |  awk '{print $2}' | aptitude purge -

pljvaldez · 05-07-2010, 05:28 PM

I guess you could also do

Code:

aptitude purge -y `dpkg -l | grep cups |  awk '{print $2}'`

grail · 05-07-2010, 11:48 PM

Code:

aptitude purge -y `dpkg -l | awk '/cups/{print $2}'`

ntubski · 05-08-2010, 11:12 AM

Code:

dpkg-query -f '${Package}\n' -W '*cups*' | aptitude purge -y -