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Re: eval a=b\ c

From: Dennis Williamson
Subject: Re: eval a=b\ c
Date: Mon, 25 May 2015 20:12:52 -0500

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


# Echo the arguments, then execute them as a command.
function echodo() {
  if [[ -n $ZSH_VERSION ]] ; then
    echo "[ ${(q)@} ]"
    eval    ${(q)@}
    echo "[ $@ ]"
    eval    $@
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



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