Re: issue with [[ -v A[\$k] ]]

[Greg Wooledge]

On Sun, May 21, 2023 at 10:35:03PM +0200, alex xmb ratchev wrote:
> q : what bash code to write to have random input as secure keys ?

1) I would avoid using the -v operator, period.  I've seen nothing but
   bug reports coming from people who try to use it.  There's even a
   BashPitfall for it <https://mywiki.wooledge.org/BashPitfalls#pf61>.
   Your backslash workaround might be OK, in some versions of bash,
   but I wouldn't trust it, especially given how many workarounds
   were broken by bash 5.2.

   Instead of using -v to test for existence of a key, use a non-empty
   value.  Then actually EXPAND the array element, and see if you get
   a non-empty string.

   hash[$key]=1

   if [[ ${hash[$key]} ]]; then     # BUT!  See part 2.
       echo "key exists"
   else
       echo "key does not exist"
   fi


2) To allow arbitrary keys, including the empty string, use the "x hack".

   hash[x$key]=1

   if [[ ${hash[x$key]} ]]; then
       echo "key exists"
   else
       echo "key does not exist"
   fi


3) Don't use an associative array expansion inside an arithmetic context,
   because of <https://mywiki.wooledge.org/BashPitfalls#pf62>.  This may
   not apply to your use of the associative array as a set, but I'll
   just mention it here for posterity.


Part 1 means you can't use set -u.  So don't use set -u.  Simple!