How does the piping in this command ultimately achieve to kill the process?

Question

I have seen the following line in a bash script for killing a process(in this case started with the command loadgen):

ps xww | grep -i "loadgen" | grep "PATTERNMATCH_FACT.xml" | cut -c1-5 | xargs -i kill {} 2>/dev/null

I would like to understand the reason for piping after the two grep's in the command above.

The way the loadgen command is started is the following. It's a part of the startup script.

./loadgen -XMLFile ${DEMODIR}/bam-103-pattern-match/data/PATTERNMATCH_FACT.xml -duration 0 -frequency 2 

Answer 1

ps xww gives the following output

...
    1 ?        Ss     0:00 init [2]
 1804 pts/0    Ss     0:00 -bash
...

After the two grep's it pipes the output to cut. This command cuts the character 1-5 out of the output. In the output above it whould be the PID's:

    1
 1804

This is piped to xargs. Xargs builds commands that look like this:

kill 1
kill 1804

and executes them. 2>/dev/null means that all error messages are sent to the pseudo device /dev/null.

So your command kills every process that is greped out of the ps command.

Or see explainshell.