Shell Trying to learn shell scripts (create own service to run on boot)

[blind0ne]

Hello, I'm trying to understand the process of starting scripts and understand shell itself.

I would like to ask:

what is $rc_fast_and_loose?
in

if [ -n "$rc_fast_and_loose" ]; then
   set $_arg; . $_file

what is -n here? is it

True if the length of "STRING" is non-zero. ?​

and what does this line with set $_arg; . $_file ? What does this . after semicolon

 

[zirias@]

Without context, most questions can't be answered, while you already answered one of your questions yourself

Leaves the ., that's the shell builtin to source another file (its contents will just be executed there by the same shell instance).

Init scripts are "special", there's a shell library /etc/rc.subr (see rc.subr(8)) for them. Here's an old intro to it, most things are still correct: https://docs.freebsd.org/en/articles/rc-scripting/

 

[SirDice]

what is -n here?

test(1)

-n	string	   True	if the length of string	is nonzero.

What does this . after semicolon

The dot is shorthand for source(1), so that line sources code from a file named in the $_file variable.

 

[Tieks]

what is $rc_fast_and_loose?

According to rc.subr() it's a variable that you can set in /etc/rc.conf. However, rc.conf() does not list rc_fast_and_loose as a valid variable. It may be a relict from a long gone past. So testing if it's a nonzero string will probably return false.

 

[Andriy]

I recommend visiting this link https://pubs.opengroup.org/onlinepubs/9699919799/toc.htm and going to Shell & Utilities section.
Shell Command Language would probably be of most interest to you.