Quoting Paul E Condon on 2010-08-20 17:36:32, in Message-Id
<[🔎] 20100820223632.GB2190@big.lan.gnu>
> i.e. they are after a statement [ -z "$PS1" ] && return which, I
> think, executes return if PS1 is empty.
ACK.
> The comment just before the above line of code is: "# If not running
> interactively, don't do anything" For me, the implication of this
> comment is that a non-empty PS1 IS the defining characteristic of
> 'running interactively', but I would have thought 'interactive' should
> be characterized by having a tty attached to sysin and sysout for
> communication to a 'user'.
s/sys/std/ as a matter of pedantry.
[ -n $PS1 ] isn't what _defines_ a shell as being interactive. That's
merely one test to determine if the shell's interactive or not. Another
test would be to see if the value of $- contains 'i'. From bash(1):
An interactive shell is one started without non-option
arguments and without the -c option whose standard input
and error are both connected to terminals (as determined
by isatty(3)), or one started with the -i option. PS1 is
set and $- includes i if bash is interactive, allowing a
shell script or a startup file to test this state.
> I can imagine that a non-empty PS1 is used as an indicator, in which
Yes, it is used as an indicator, as stated above.
> case whatever code that actually sets up the tty also sets PS1 to some
> minimal non-empty value like a single space or a dot, but is this
> actually the way it works, and where is it?
It's actually the shell that sets $PS1 on startup. I don't have the bash
source (or 1003.2 if it's defined there) on hand as I'm composing this
offline, so I leave finding exactly where and how an exercise to the
reader.
While technically you CAN set PS1=' ', or even unset PS1, I wouldn't
recommend it. The smallest I'd recommend setting it to is '\W:\$ ', or
'\$ ' (note the trailing spaces). The former displays just the last
component of your current directory, and the latter doesn't even display
that, just a $ (or # if you're root)
I further recommend against unsetting PS1 as without some kind of prompt
you have little visual indication your current process is finished. A
demonstration:
bryans@esterhazy:~ OLDPS1=$PS1
bryans@esterhazy:~ unset PS1
find ~ -name "`apgwrap`" && echo done # [1] [2]
done
[1] apgwrap is the following:
#!/bin/sh
apg -a0 -n1 -m10 -x12 -MNCL -tc $(dd if=/dev/urandom bs=16 count=1 2>/dev/null)
[2] the 'echo done' is there only to show when the process is finished.
Without it I'd likely have sat waiting for quite a while.
> Where can I read about these issues?
See bash(1), or the info document for it if you have it installed.
> Puzzled.
Hope this explanation helps.
--
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