On Sun, Feb 17, 2019 at 08:07:06PM -0500, Chet Ramey wrote:
> On 2/16/19 11:38 AM, sunnycemet...@gmail.com wrote:
> > I would like to include a null string as part of a parameter expansion word:
> >
> >> mapfile -t${bNullDelimited+d ''}
> >
> > When bNullDelimited is set, I expect this to expand to:
> >
> >> mapfile -td ''
> >
> > However, it expands to:
> >
> >> mapfile -td
>
> There are mixed behaviors. The idea behind the bash behavior is that a
> null string added to a non-empty word is simply discarded, and this happens
> while the word after the `+' is being processed, before word splitting.
>
> bash/ksh93/zsh do it one way, ash-derived shells/mksh/yash do it another.
Ugh. Shells are so messy.
wooledg:~$ ksh
$ args ${PATH+d ''}
1 args: <d>
wooledg:~$ dash
$ args ${PATH+d ''}
2 args: <d> <>
Looks like the best workaround (for bash/ksh) is to store the -d '' args
in an array, and use something like:
mapfile -t ${bNullDelimited+"${tmparray[@]}"}
This works in both ksh and bash; I did not test anything else (and of
course dash and other close-to-POSIX shells don't even *have* arrays, so
it's a good thing the workaround isn't needed there).
Then again, mapfile is bash-only, so you probably aren't looking for a
great level of portability here.
