Re: [Help-bash] How to extrapolate bash string?

[Eric Blake]

On 09/11/2013 10:22 PM, Chris Down wrote:
> On 2013-09-11 22:30, Peng Yu wrote:
>> This message does not seem to provide a solution. If 'eval' is not
>> used, what else can be used?
> 
> It's a thread, I'm not referring to that individual message.

In particular,
https://lists.gnu.org/archive/html/bug-bash/2013-04/msg00051.html mentions:

case $1 in
  \~ )
    printf '%s\n' "$HOME" ;;
  \~/* )
    printf '%s\n' "$HOME/${1#??}" ;;
  \~* )
    user=${1%%/*}
    path=${1#*/}
    # Sanitize user before feeding it to eval.
    # You must adjust this code based on what characters are legal in your
    # system's usernames.  If your system allows shell metacharacters in
    # usernames, you are screwed.  Just give up now (switch to perl).
    user=${user#\~}
    user2=${user//[^[:alnum:]._-]/}
    if [[ $user != "$user2" ]]; then
      echo "Error: invalid characters in username" >&2
      exit 1
    fi
    eval "home=~$user2"
    case $1 in
      */* ) printf '%s\n' "$home/$path" ;;
      *   ) printf '%s\n' "$home" ;;
    esac ;;
  * )
    printf '%s\n' "$1" ;;
esac

and followups pointed out that instead of erroring out for shell
metacharacters, that it should just print them as-is (after all, the
only way to combine ~ and a metacharacter into a single word is to use
quoting, but quoting disables tilde-expansion).

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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