Shell Programming and Scripting

Ok, I have been trying my very best to solve this, but with no success.

My goal is to write a 'before' and 'after' script to track which processes are added after starting a program.
I will use it to track what been added when I install programs that autostart, and probably call that script whenever I install a program from cli.

first I save the processes - so far no problem.

Code:

 ps -e > ./before

Then I want to exclude the processes which I saved .

Code:

cat ./before |awk '$1{printf "%s ",  $1 }' | xargs ps -N > ./after

= FAIL



I am thankfoul to every comment and / or ideas to go another direction to get the needed result.

/Swepter

You don't need to use printf to put them all in a line for xargs, just one on a line works too.

That's also a useless use of cat.

I think it failed because you're failing to exclude things like the first line. This works here:

Code:

ps -e | awk '(NR>1) && ($0=$1)' > before
xargs ps -N < before

Also beware that, if the number of processes on the system exceeds the maximum number of arguments, ps -N will be split into two calls, which will produce very wrong results.

I don't really understand ...
My idea is to save the complete output of ps -e to the file named ./before (I want to keep the file for future), and then use the first columns as input for the processes to exclude when saving the next output of ps, hence the -N switch. (I should rather name the file to diff_after).

Also - when trying to execute the last line in your example, I got this error:

bash: after: No such file or directory

which to me seems naturally as it performs a read from the file which is not yet created.

And yes, I am quite noobish - so maybe I am doing something wrong when following your example.?

Code:

ps -e > ./before
awk 'NR>1 {print $1}' ./before | xargs ps -N > ./after

That seems to work, thankyou :-)

Ooof. My bad. I meant to use the 'before' file. I had both hanging around after a lot of fiddling to get it to work, so it worked anyway...