FAQ that --nofilter is required for headless use

[n1vux]

per @petdance comment on beyondgrep/ack2#649 , we need more FAQ re the non-TTY ignoring of ARGV unless --nofilter re-enables. It is not obvious to users who don't read CHANGES superclosely, and even 2 of 3 of us didn't remember that was the obvious problem with crontab immediately. So needs more Google SEO at a minimum. (Could consider adding alias --headless?)

[petdance]

What does "headless" mean? I've never heard that time before.

[n1vux]

What does "headless" mean? I've never heard that time before.

non-interactive; unattended.
(inclusive of, more general than, both "pure batch" and "daemons"; thus including crontab but also services built as shell scripts.)

a 'headless server' has no graphics device attached, so nowhere for popup dialogs to be ignored even.
So by analogy, a shell or process is 'headless' if it's got no /dev/tty to spew interactive warnings to.

(I thought nohup background would be equivalently headless, but until I actually log out, nohup bash -c "echo FOO > /dev/tty" & still writes to tty. I'm failing to remember how to emulate the crontab or daemon lack of tty without setting up pipe or calling ioctl explicitly.)