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Re: Variable var names

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On 2026-06-12 09:30, Frank Winkler wrote:
> Hi there !

You've already got a couple useful hints and explanations. So just
some additional hints...

Below, consider using arrays instead of manipulating variable names.
(Thereby you avoid the 'eval' that you've already been suggested to
avoid in the first place, if not really necessary.)

   x=( "" "  ok  " "  not ok  " )
   echo ${x[1]}
   echo ${x[2]}

Standard arrays are counted from 0 so the first array element has
a dummy element above. (Modern shells also support associative
arrays, in case you want more flexibility.)

If you want for (some reason) to use 'eval' note that you can, as
suggested, use two layers of quotes (one escaped), or just use two
different nested quotes ( " and ' ), but also note the effects of
expansions inside the double-quotes; you can take that for your
advantage (if you know the expansion rules).

The effect of IFS changes on _internal_ shell commands like 'eval'
have been explained already, and that this is standard behavior.
Note that you don't need to save/restore the IFS in standard code;
you can also embed it in a subshell-environment with parenthesis
to keep the IFS change local within the parenthesis, as in

   ( IFS="" eval echo ".\$x$n." )

In ksh you won't create a real subshell that way if there's only
shell built-ins like 'eval' and 'echo' used, so it's efficient.

If you intend to use mainly "modern" shells like bash, ksh, zsh,
you should consider using (instead of [ ... ]) [[ ... ]], or in
case of arithmetic (as in your code below) the shell's arithmetic
statement

   (( n == 1 )) && ..

For many values you may also use 'case',

   case $n in
   (1) ... ;;
   (2) ... ;;
   (*) ... ;;  # default branch for errors
   esac

And of course use 'printf' (instead of 'echo').

Janis

> 
> I'm playing with the following in an interactive bash as well as in a 
> ksh script:
> 
> $ n=1
> $ x1="  ok  "
> $ x2="  not ok  "
> $ eval echo \$x$n
> ok
> $ eval echo "\$x$n"
> ok
> $ n=2
> $ eval echo "\$x$n"
> not ok
> $
> 
> So the variable var name seems to work but why are the blanks "deleted" 
> here? I also tried some variants with "printf", but also with no success.
> 
> Just out of curiosity, I tried this:
> 
> $ IFS="" eval echo ".\$x$n."
> .  not ok  .
> $
> 
> To my surprise, it works but why is IFS relevant here? And to my even 
> bigger surprise, it looks like everything seems to behave as expected in 
> the bash session but in the ksh script, IFS is not just changed for this 
> single command but globally - so I had to save and restore it to prevent 
> the whole script from exploding. This makes the interesting part much 
> longer and more complicated, eating up the potential advantage and 
> coolness superiority over just doing something like
> 
>    [ $n -eq 1 ] && echo "$x1"
>    [ $n -eq 2 ] && echo "$x2"
> 
> Any hints from the experts?
> 
> TIA
> 
>      Frank
> 

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Variable var names Frank Winkler <usenet@f.winkler-ka.de> - 2026-06-12 09:30 +0200
  Re: Variable var names gazelle@shell.xmission.com (Kenny McCormack) - 2026-06-12 09:02 +0000
    Re: Variable var names Frank Winkler <usenet@f.winkler-ka.de> - 2026-06-13 12:29 +0200
      Re: Variable var names gazelle@shell.xmission.com (Kenny McCormack) - 2026-06-13 11:14 +0000
      Re: Variable var names Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-06-13 13:15 +0200
  Re: Variable var names ram@zedat.fu-berlin.de (Stefan Ram) - 2026-06-12 11:26 +0000
    Re: Variable var names ram@zedat.fu-berlin.de (Stefan Ram) - 2026-06-12 11:38 +0000
      Re: Variable var names Frank Winkler <usenet@f.winkler-ka.de> - 2026-06-12 14:07 +0200
        Re: Variable var names ram@zedat.fu-berlin.de (Stefan Ram) - 2026-06-12 12:31 +0000
          Re: Variable var names Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-06-13 02:48 +0000
  Re: Variable var names Christian Weisgerber <naddy@mips.inka.de> - 2026-06-12 12:12 +0000
    Re: Variable var names Frank Winkler <usenet@f.winkler-ka.de> - 2026-06-12 15:19 +0200
    Re: Variable var names Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-06-13 02:51 +0000
  Re: Variable var names Geoff Clare <geoff@clare.See-My-Signature.invalid> - 2026-06-12 13:42 +0100
  Re: Variable var names Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-06-12 17:41 +0200
    Re: Variable var names Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-06-12 17:54 +0200
    Re: Variable var names Frank Winkler <usenet@f.winkler-ka.de> - 2026-06-13 12:32 +0200
      Re: Variable var names Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-06-14 01:12 +0000
  Re: Variable var names Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-06-13 00:20 +0000
  Re: Variable var names Kaz Kylheku <046-301-5902@kylheku.com> - 2026-06-23 21:25 +0000
    Re: Variable var names Helmut Waitzmann <nn.throttle@erine.email> - 2026-06-24 10:45 +0200
    Re: Variable var names Christian Weisgerber <naddy@mips.inka.de> - 2026-06-24 11:41 +0000

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