Re: PS-embedded comsub `\w' evaluation doesn't replace $HOME with ~

[Rob Foehl]

On Sun, 12 Mar 2017, Grisha Levit wrote:

> For example:
>
> $ PS1='\w $(echo \w) $ '
> ~ /home/levit $

This seems to work as documented, for the same reason this happens:

╶➤ echo ~
/home/rob

The expansion order is perhaps non-obvious: the prompt string backslash 
escapes are replaced before the string is subject to any other expansions.

> Obviously, this is easy enough to work around in most cases by
> replacing \w with ${PWD/#$HOME/~}.  I had a silly application for
> calculating prompt length and this was throwing it off, but this
> behavior has been there since at least 2.05b so not sure if it's worth
> changing..

Doing anything that depends on calculating (any part of) the prompt length 
at expansion time in PS1 is... complicated.

╶➤ echo ${#PS1}
1485

I have on occasion wondered how difficult it'd be to make ${#...} 
applicable to any arbitrary expansion, but I also can't think of another 
use case...

-Rob