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Re: eval a=b\ c


From: Dave Yost
Subject: Re: eval a=b\ c
Date: Wed, 27 May 2015 00:59:53 -0700

OK, I can make it to work in bash if I say
  echodo a=b\\ c
but then zsh tries to execute c. Can’t win.

The problem is: how do I write this function so that it can be invoked 
identically in zsh and bash with identical results of setting a variable to a 
value with a space in it?

> On 2015-05-26, at 1:04 AM, Andreas Schwab <address@hidden> wrote:
> 
> address@hidden writes:
> 
>>    eval    $@
> 
> You are expanding a shell parameter unquoted.  Never do that unless you
> know what you are doing.
> 
>      eval "$@"
> 
> Andreas.
> 
> -- 
> Andreas Schwab, SUSE Labs, address@hidden
> GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
> "And now for something completely different."


On 2015-05-25, at 6:12 PM, Dennis Williamson <address@hidden> wrote:

> I'm trying to put a command in a variable, but the complex cases always fail! 
> : http://mywiki.wooledge.org/BashFAQ/050
> 
> Eval command and security issues : http://mywiki.wooledge.org/BashFAQ/048
> 
> On Mon, May 25, 2015 at 2:33 PM,  <address@hidden> wrote:
> Configuration Information [Automatically generated, do not change]:
> Machine: x86_64
> OS: linux-gnu
> Compiler: gcc
> Compilation CFLAGS:  -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64' 
> -DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='x86_64-unknown-linux-gnu' 
> -DCONF_VENDOR='unknown' -DLOCALEDIR='/usr/local/bash/4.3.39/share/locale' 
> -DPACKAGE='bash' -DSHELL -DHAVE_CONFIG_H   -I.  -I../bash-4.3 
> -I../bash-4.3/include -I../bash-4.3/lib   -g -O2
> uname output: Linux s6.millcomputing.com 2.6.32-504.16.2.el6.x86_64 #1 SMP 
> Wed Apr 22 06:48:29 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
> Machine Type: x86_64-unknown-linux-gnu
> 
> Bash Version: 4.3
> Patch Level: 39
> Release Status: release
> 
> Description:
> 
> # Echo the arguments, then execute them as a command.
> function echodo() {
>   if [[ -n $ZSH_VERSION ]] ; then
>     echo "[ ${(q)@} ]"
>     eval    ${(q)@}
>   else
>     echo "[ $@ ]"
>     eval    $@
>   fi
> }
> echodo echo b\ c
> echodo a=b\ c
> echo $a
> 
> The result in zsh is:
>   $ echodo echo b\ c
>   [ echo b\ c ]
>   b c
>   $ echodo a=b\ c
>   [ a=b\ c ]
>   $ echo $a
>   b c
>   $
> 
> Bash gets an error:
>   $ echodo echo b\ c
>   [ echo b c ]
>   b c
>   $ echodo a=b\ c
>   [ a=b c ]
>   bash: c: command not found
>   $ echo $a
> 
>   $
> 
> I can't find a way to implement echodo in bash. Apparently this is because 
> bash is unable to expand a variable with quoting intact, as zsh can do with 
> its (q) expansion flag.
> 
> Bash behaves differently in this case::
> 
>   $ echodo export a=b\ c
>   [ export a=b c ]
>   $ echo $a
>   b
>   $
> 
> 
> Repeat-By:
> 
> 
> 
> Fix:
> 
> 
> 
> 
> -- 
> Visit serverfault.com to get your system administration questions answered.
> 



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