Description of problem:

I was writing a shell script, and I was wondering why does it take 0.66s for it
to print out usage information. Indeed it was bash_completion. First disabled
it, time down to 0.09s. Neat. But then I simply added a single magic line to
/etc/profile.d/bash_completion.sh:

[ -z "$PS1" ] && return

so it doesn't run in non-interactive shells.  Somebody suggested the more
correct solution:

[[ $- == *i* ]] && return