Re: [Help-bash] Transform strings with special characters so that the strings don't need to be quoted?

[Stephane Chazelas]

2015-03-30 09:47:16 -0400, Greg Wooledge:
> On Mon, Mar 30, 2015 at 02:02:10PM +0100, Stephane Chazelas wrote:
[...]
> > var=$(cmd && echo .) && var=${var%?} && var=${var%?}
> > (to remove only one newline)
> > 
> > but that's obviously a pain.
> 
> In #bash we (de facto) agreed on this version:
> 
> var=$(cmd; printf x) var=${var%x}
> 
> Which is basically the same as yours 

That doesn't trim the one trailing newline you usually want to
trim (which was the point of my two var=${var%?}) and that fails
to preserve the exit status of cmd though.

There's a tradeoff in the solution I gave as well in that it
won't preserve the trailing newlines if cmd fails.

I often do:

var=$(cmd && echo .) || exit
var=${var%?}; var=${var%?}

Where that's not a problem.

A complete solution would be:

var=$(cmd; ret=$?; echo .; exit -- "$ret")
ret=$?
var=${var%?}; var=${var%?}
(exit -- "$ret")

Probably better at that point defining a function for that, like
that I gave at https://unix.stackexchange.com/a/120775 where we
discussed that before.

cmdsubst() {
  local _ret _var
  _var=$1; shift

  eval "$_var"'=$("$@"; _ret=$?; echo .; exit -- "$_ret")
    _ret=$?
    '"$_var=\${$_var%?}; $_var=\${$_var%?}"
  return -- "$_ret"
}

And use as:

cmdsubst var cmd args...

(yes, I know "--" is currently not needed for current versions
of bash, that's just me being paranoidly future-proof in case
bash starts allowing negative values or arbitrary strings for
return like rc/es in the future;-))

-- 
Stephane