What is awk '{ print $2; }' doing exactly?

I would like to know what is this statement doing exactly, especially the awk part.

ps aux | grep 'sidekiq 5' | grep -v grep | awk '{ print $2; }' | xargs kill -${2:-'TERM'}

I know the entire pipeline is supposed to kill sidekiq processes.

1 Answer

ps aux lists all processes.
grep 'sidekiq 5' only displays those lines from the list that contain the string "sidekiq 5".
grep -v grep removes those lines that contain the string "grep". This is done so that the grep process from the previous pipeline stage is filtered out.
awk '{ print $2; }' prints the second field of each line. This field happens to be the process ID from the ps aux output.
xargs kill -${2:-'TERM'} takes the process IDs from the selected sidekiq processes and feeds them as arguments to a kill command. The signal is either $2 or, if $2 is not defined, SIGTERM.