Command behavior is different when executed by an other user (via su -c)

Question

I want to kill every processes who match a specific chain. Here is my script, which works pretty well:

echo `ps aux | grep verySpecificChain | grep -v grep | /usr/bin/awk '{ print $2 }'` | xargs kill

Now I want to execute this script from an other user via `su -c:

echo password | su -c "echo `ps aux | grep verySpecificChain | grep -v grep | /usr/bin/awk '{ print $2 }'` | xargs kill" userName;

My problem is that when grep verySpecificChain matches several processes, only the first element is passed to xargs kill:

30598  ==> killed
bash: line 1: 30599: command not found  ==> Not killed
bash: line 2: 30600: command not found  ==> Not killed
bash: line 3: 30606: command not found  ==> Not killed

I really would like to understand why with or without su -c the command behaviour changes?

I'm running GNU bash, version 4.2.53(1)-release (x86_64-redhat-linux-gnu) on Fedora 20.

Answer 1

Just pkill -f verySpecificChain

Answer 2

I cannot explain what exactly fails in your example (so I admit it is some kind of voodoo programming on my side), but this is a fix that (almost -- see below*) works in my bash (Debian):

• get rid of inside echo;
• escape $2.

Result:

echo password | su -c "ps aux | grep verySpecificChain | grep -v grep | /usr/bin/awk '{ print \$2 }' | xargs kill" userName;

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*I wrote "almost works" because Debian won't let me use su in a pipe to echo the password. I must run it without initial echo and type the password interactively. I guess it's not an issue in OP's Fedora.