Re: BASH Command substitution

[Chris F.A. Johnson]

On Thu, 17 Dec 2009, Zoltan Mate wrote:

> Dear Chet Ramey,
> 
> I have a conversation on an other bug forum, then have been directed
> to here, I cannot find any documentation, why
> 
> $ echo $(echo "'alfa  beta'")
> gives 'alfa beta' whith reduced space, instead of the result of the
> following more logical ways:
> 
> $ echo $(echo "'alfa  beta'")
> the second term suggests one parameter being substituted as
> "<the output of the command>"
> 
> On the other hand, having made the substitution, one should get the
> $ echo 'alfa  beta'
> text to be interpreted.
> 
> 
> So why the '-s are quoted and the spaces are not?
> This strange behaviour should be mentioned in the bash manual.

   The output of the command substitution is two arguments. It you
   want it intepreted as one, quote it:

echo "$(echo "'alfa  beta'")"


> ----------------------------------------- The former conversation:
> --------------------------------------------
> bash command substitution reduce double spaces in strings:
> 
> $ echo $(echo "'alfa  beta'")
> 'alfa beta'
> 
> 
> Reproducible: Always
> 
> Steps to Reproduce:
> 
> 
> ------- Comment #1 From SpanKY 2009-12-16 19:32:24 0000 [reply] -------
> 
> the second isnt actually quoted which means you ran:
> argv[] = {
>     "echo"
>     "'alfa"
>     "beta'"
> }
> 
> 
> ------- Comment #2 From ZoliM 2009-12-17 09:41:08 0000 [reply] -------
> 
> Where is emphasized the text interpreatation process in the manual?
> 
> In
> $ echo $(echo "'alfa  beta'")
> the second term suggests one parameter being substituted as
> "<the output of the command>"
> 
> On the other hand, having made the substitution, one should get the
> $ echo 'alfa  beta'
> text to be interpreted.
> 
> So I motion to mark in the documentation at the Command substitution chapter
> the proper interpretation logic.
> 
> 
> ------- Comment #3 From SpanKY 2009-12-17 10:32:32 0000 [reply] -------
> 
> those two examples are not equivalent.  your first snippet boils down to:
> echo \'alfa  beta\'
> 
> this bugzilla isnt a forum for teaching people how to script bash.  if you 
> want
> further help, please ask on the bash mailing list, or the gentoo forums, or
> some other suitable location.

-- 
   Chris F.A. Johnson, webmaster         <http://woodbine-gerrard.com>
   ===================================================================
   Author:
   Shell Scripting Recipes: A Problem-Solution Approach (2005, Apress)
   Pro Bash Programming: Scripting the GNU/Linux Shell (2009, Apress)