On Fri, Aug 26, 2022 at 11:14:37AM +0100, Tim Woodall wrote:
> $ bash -uic 'echo done'
> bash: SUDO_USER: unbound variable
> bash: color_prompt: unbound variable
> done
> $
Cute. Mine's even weirder:
unicorn:~$ bash -uic 'echo done'
bash: SUDO_USER: unbound variable
bash: no: unbound variable
done
It turns out, this is due to the following line in my .bashrc:
MAILCHECK=no
I can't even remember putting that in there. Here's what the man page
says:
MAILCHECK
Specifies how often (in seconds) bash checks for mail. The de‐
fault is 60 seconds. When it is time to check for mail, the
shell does so before displaying the primary prompt. If this
variable is unset, or set to a value that is not a number
greater than or equal to zero, the shell disables mail checking.
Apparently "not a number greater than or equal to zero" must not mean
what I thought it meant, at the time I wrote that line.
At some point, bash must have given MAILCHECK the "integer attribute",
which means that MAILCHECK=no is attempting assignment to an *arithmetic*
variable, which means it performs a recursive expansion on the word "no"
in an arithmetic context -- which makes it treat "no" as a shell variable
to be expanded. Hence the complaint from -u.
Without -u, and without a "no" variable, the effect is basically
MAILCHECK=0 which is clearly not what I wanted.
Fortunately, it's entirely moot, because in context, I have this:
MAILCHECK=no
unset MAILCHECK # Takes too damned long.
I guess I should just comment out the first line, then. There's no point
keeping it there.
So, today I guess I learned that MAILCHECK gained the integer attribute
at some point. I wonder when... well, let's find out.
...
unicorn:~$ bash-3.1 -uic :
bash-3.1: no: unbound variable
unicorn:~$ bash-3.0 -uic :
unicorn:~$
Looks like it happened in bash 3.1.
*Now* I'll comment out that line in my .bashrc.
